guestfs_mount (g, "/dev/sda1", "/");
guestfs_touch (g, "/hello");
guestfs_umount (g, "/");
- guestfs_sync (g);
guestfs_close (g);
cc prog.c -o prog -lguestfs
Libguestfs is a library that can be linked with C and C++ management
programs (or management programs written in OCaml, Perl, Python, Ruby,
-Java, Haskell or C#). You can also use it from shell scripts or the
+Java, PHP, Haskell or C#). You can also use it from shell scripts or the
command line.
You don't need to be root to use libguestfs, although obviously you do
Libguestfs is a large API because it can do many things. For a gentle
introduction, please read the L</API OVERVIEW> section next.
+There are also some example programs in the L<guestfs-examples(3)>
+manual page.
+
=head1 API OVERVIEW
This section provides a gentler overview of the libguestfs API. We
*/
guestfs_touch (g, "/hello");
- /* You only need to call guestfs_sync if you have made
- * changes to the guest image. (But if you've made changes
- * then you *must* sync). See also: guestfs_umount and
- * guestfs_umount_all calls.
+ /* This is only needed for libguestfs < 1.5.24. Since then
+ * it is done automatically when you close the handle. See
+ * discussion of autosync in this page.
*/
guestfs_sync (g);
functions that return pointers return C<NULL> on error. See section
L</ERROR HANDLING> below for how to handle errors, and consult the
documentation for each function call below to see precisely how they
-return error indications.
+return error indications. See L<guestfs-examples(3)> for fully worked
+examples.
=head2 DISK IMAGES
you have created through L<posix_fallocate(3)>. Libguestfs lets you
do useful things to all of these.
-You can add a disk read-only using L</guestfs_add_drive_ro>, in which
+The call you should use in modern code for adding drives is
+L</guestfs_add_drive_opts>. To add a disk image, allowing writes, and
+specifying that the format is raw, do:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
+ -1);
+
+You can add a disk read-only using:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
+ GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+ -1);
+
+or by calling the older function L</guestfs_add_drive_ro>. In either
case libguestfs won't modify the file.
Be extremely cautious if the disk image is in use, eg. if it is being
Before you can read or write files, create directories and so on in a
disk image that contains filesystems, you have to mount those
-filesystems using L</guestfs_mount>. If you already know that a disk
-image contains (for example) one partition with a filesystem on that
-partition, then you can mount it directly:
+filesystems using L</guestfs_mount_options> or L</guestfs_mount_ro>.
+If you already know that a disk image contains (for example) one
+partition with a filesystem on that partition, then you can mount it
+directly:
- guestfs_mount (g, "/dev/sda1", "/");
+ guestfs_mount_options (g, "", "/dev/sda1", "/");
where C</dev/sda1> means literally the first partition (C<1>) of the
first disk image that we added (C</dev/sda>). If the disk contains
-Linux LVM2 logical volumes you could refer to those instead (eg. C</dev/VG/LV>).
+Linux LVM2 logical volumes you could refer to those instead
+(eg. C</dev/VG/LV>). Note that these are libguestfs virtual devices,
+and are nothing to do with host devices.
If you are given a disk image and you don't know what it contains then
you have to find out. Libguestfs can do that too: use
L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
partitions and LVs, and either try mounting each to see what is
mountable, or else examine them with L</guestfs_vfs_type> or
-L</guestfs_file>. But you might find it easier to look at higher level
-programs built on top of libguestfs, in particular
-L<virt-inspector(1)>.
+L</guestfs_file>. To list just filesystems, use
+L</guestfs_list_filesystems>.
+
+Libguestfs also has a set of APIs for inspection of unknown disk
+images (see L</INSPECTION> below). But you might find it easier to
+look at higher level programs built on top of libguestfs, in
+particular L<virt-inspector(1)>.
-To mount a disk image read-only, use L</guestfs_mount_ro>. There are
+To mount a filesystem read-only, use L</guestfs_mount_ro>. There are
several other variations of the C<guestfs_mount_*> call.
=head2 FILESYSTEM ACCESS AND MODIFICATION
=head2 DOWNLOADING
-Use L</guestfs_cat> to download small, text only files. This call
-is limited to files which are less than 2 MB and which cannot contain
-any ASCII NUL (C<\0>) characters. However it has a very simple
-to use API.
+Use L</guestfs_cat> to download small, text only files. This call is
+limited to files which are less than 2 MB and which cannot contain any
+ASCII NUL (C<\0>) characters. However the API is very simple to use.
L</guestfs_read_file> can be used to read files which contain
arbitrary 8 bit data, since it returns a (pointer, size) pair.
It's often the case that you want to write a file or files to the disk
image.
-For small, single files, use L</guestfs_write_file>. This call
-currently contains a bug which limits the call to plain text files
-(not containing ASCII NUL characters).
+To write a small file with fixed content, use L</guestfs_write>. To
+create a file of all zeroes, use L</guestfs_truncate_size> (sparse) or
+L</guestfs_fallocate64> (with all disk blocks allocated). There are a
+variety of other functions for creating test files, for example
+L</guestfs_fill> and L</guestfs_fill_pattern>.
To upload a single file, use L</guestfs_upload>. This call has no
limits on file content or size (even files larger than 4 GB).
=back
+=head2 UPLOADING AND DOWNLOADING TO PIPES AND FILE DESCRIPTORS
+
+Calls like L</guestfs_upload>, L</guestfs_download>,
+L</guestfs_tar_in>, L</guestfs_tar_out> etc appear to only take
+filenames as arguments, so it appears you can only upload and download
+to files. However many Un*x-like hosts let you use the special device
+files C</dev/stdin>, C</dev/stdout>, C</dev/stderr> and C</dev/fd/N>
+to read and write from stdin, stdout, stderr, and arbitrary file
+descriptor N.
+
+For example, L<virt-cat(1)> writes its output to stdout by
+doing:
+
+ guestfs_download (g, filename, "/dev/stdout");
+
+and you can write tar output to a file descriptor C<fd> by doing:
+
+ char devfd[64];
+ snprintf (devfd, sizeof devfd, "/dev/fd/%d", fd);
+ guestfs_tar_out (g, "/", devfd);
+
=head2 LISTING FILES
L</guestfs_ll> is just designed for humans to read (mainly when using
=head2 RUNNING COMMANDS
-Although libguestfs is a primarily an API for manipulating files
+Although libguestfs is primarily an API for manipulating files
inside guest images, we also provide some limited facilities for
running commands inside guests.
=item *
+The network may not be available unless you enable it
+(see L</guestfs_set_network>).
+
+=item *
+
Only supports Linux guests (not Windows, BSD, etc).
=item *
For SELinux guests, you may need to enable SELinux and load policy
first. See L</SELINUX> in this manpage.
+=item *
+
+I<Security:> It is not safe to run commands from untrusted, possibly
+malicious guests. These commands may attempt to exploit your program
+by sending unexpected output. They could also try to exploit the
+Linux kernel or qemu provided by the libguestfs appliance. They could
+use the network provided by the libguestfs appliance to bypass
+ordinary network partitions and firewalls. They could use the
+elevated privileges or different SELinux context of your program
+to their advantage.
+
+A secure alternative is to use libguestfs to install a "firstboot"
+script (a script which runs when the guest next boots normally), and
+to have this script run the commands you want in the normal context of
+the running guest, network security and so on. For information about
+other security issues, see L</SECURITY>.
+
=back
The two main API calls to run commands are L</guestfs_command> and
For more information about umask, see L<umask(2)>.
+=head2 ENCRYPTED DISKS
+
+Libguestfs allows you to access Linux guests which have been
+encrypted using whole disk encryption that conforms to the
+Linux Unified Key Setup (LUKS) standard. This includes
+nearly all whole disk encryption systems used by modern
+Linux guests.
+
+Use L</guestfs_vfs_type> to identify LUKS-encrypted block
+devices (it returns the string C<crypto_LUKS>).
+
+Then open these devices by calling L</guestfs_luks_open>.
+Obviously you will require the passphrase!
+
+Opening a LUKS device creates a new device mapper device
+called C</dev/mapper/mapname> (where C<mapname> is the
+string you supply to L</guestfs_luks_open>).
+Reads and writes to this mapper device are decrypted from and
+encrypted to the underlying block device respectively.
+
+LVM volume groups on the device can be made visible by calling
+L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
+The logical volume(s) can now be mounted in the usual way.
+
+Use the reverse process to close a LUKS device. Unmount
+any logical volumes on it, deactivate the volume groups
+by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
+Then close the mapper device by calling
+L</guestfs_luks_close> on the C</dev/mapper/mapname>
+device (I<not> the underlying encrypted block device).
+
+=head2 INSPECTION
+
+Libguestfs has APIs for inspecting an unknown disk image to find out
+if it contains operating systems, an install CD or a live CD. (These
+APIs used to be in a separate Perl-only library called
+L<Sys::Guestfs::Lib(3)> but since version 1.5.3 the most frequently
+used part of this library has been rewritten in C and moved into the
+core code).
+
+Add all disks belonging to the unknown virtual machine and call
+L</guestfs_launch> in the usual way.
+
+Then call L</guestfs_inspect_os>. This function uses other libguestfs
+calls and certain heuristics, and returns a list of operating systems
+that were found. An empty list means none were found. A single
+element is the root filesystem of the operating system. For dual- or
+multi-boot guests, multiple roots can be returned, each one
+corresponding to a separate operating system. (Multi-boot virtual
+machines are extremely rare in the world of virtualization, but since
+this scenario can happen, we have built libguestfs to deal with it.)
+
+For each root, you can then call various C<guestfs_inspect_get_*>
+functions to get additional details about that operating system. For
+example, call L</guestfs_inspect_get_type> to return the string
+C<windows> or C<linux> for Windows and Linux-based operating systems
+respectively.
+
+Un*x-like and Linux-based operating systems usually consist of several
+filesystems which are mounted at boot time (for example, a separate
+boot partition mounted on C</boot>). The inspection rules are able to
+detect how filesystems correspond to mount points. Call
+C<guestfs_inspect_get_mountpoints> to get this mapping. It might
+return a hash table like this example:
+
+ /boot => /dev/sda1
+ / => /dev/vg_guest/lv_root
+ /usr => /dev/vg_guest/lv_usr
+
+The caller can then make calls to L</guestfs_mount_options> to
+mount the filesystems as suggested.
+
+Be careful to mount filesystems in the right order (eg. C</> before
+C</usr>). Sorting the keys of the hash by length, shortest first,
+should work.
+
+Inspection currently only works for some common operating systems.
+Contributors are welcome to send patches for other operating systems
+that we currently cannot detect.
+
+Encrypted disks must be opened before inspection. See
+L</ENCRYPTED DISKS> for more details. The L</guestfs_inspect_os>
+function just ignores any encrypted devices.
+
+A note on the implementation: The call L</guestfs_inspect_os> performs
+inspection and caches the results in the guest handle. Subsequent
+calls to C<guestfs_inspect_get_*> return this cached information, but
+I<do not> re-read the disks. If you change the content of the guest
+disks, you can redo inspection by calling L</guestfs_inspect_os>
+again. (L</guestfs_inspect_list_applications> works a little
+differently from the other calls and does read the disks. See
+documentation for that function for details).
+
+=head3 INSPECTING INSTALL DISKS
+
+Libguestfs (since 1.9.4) can detect some install disks, install
+CDs, live CDs and more.
+
+Call L</guestfs_inspect_get_format> to return the format of the
+operating system, which currently can be C<installed> (a regular
+operating system) or C<installer> (some sort of install disk).
+
+Further information is available about the operating system that can
+be installed using the regular inspection APIs like
+L</guestfs_inspect_get_product_name>,
+L</guestfs_inspect_get_major_version> etc.
+
+Some additional information specific to installer disks is also
+available from the L</guestfs_inspect_is_live>,
+L</guestfs_inspect_is_netinst> and L</guestfs_inspect_is_multipart>
+calls.
+
=head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
Libguestfs can mount NTFS partitions. It does this using the
L<http://www.ntfs-3g.org/> driver.
+=head3 DRIVE LETTERS AND PATHS
+
DOS and Windows still use drive letters, and the filesystems are
always treated as case insensitive by Windows itself, and therefore
you might find a Windows configuration file referring to a path like
C<c:\windows\system32>. When the filesystem is mounted in libguestfs,
that directory might be referred to as C</WINDOWS/System32>.
-Drive letter mappings are outside the scope of libguestfs. You have
-to use libguestfs to read the appropriate Windows Registry and
-configuration files, to determine yourself how drives are mapped (see
-also L<virt-inspector(1)>).
+Drive letter mappings can be found using inspection
+(see L</INSPECTION> and L</guestfs_inspect_get_drive_mappings>)
-Replacing backslash characters with forward slash characters is also
-outside the scope of libguestfs, but something that you can easily do.
+Dealing with separator characters (backslash vs forward slash) is
+outside the scope of libguestfs, but usually a simple character
+replacement will work.
-Where we can help is in resolving the case insensitivity of paths.
-For this, call L</guestfs_case_sensitive_path>.
+To resolve the case insensitivity of paths, call
+L</guestfs_case_sensitive_path>.
+
+=head3 ACCESSING THE WINDOWS REGISTRY
Libguestfs also provides some help for decoding Windows Registry
"hive" files, through the library C<hivex> which is part of the
L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
on this issue.
+=head3 SYMLINKS ON NTFS-3G FILESYSTEMS
+
+Ntfs-3g tries to rewrite "Junction Points" and NTFS "symbolic links"
+to provide something which looks like a Linux symlink. The way it
+tries to do the rewriting is described here:
+
+L<http://www.tuxera.com/community/ntfs-3g-advanced/junction-points-and-symbolic-links/>
+
+The essential problem is that ntfs-3g simply does not have enough
+information to do a correct job. NTFS links can contain drive letters
+and references to external device GUIDs that ntfs-3g has no way of
+resolving. It is almost certainly the case that libguestfs callers
+should ignore what ntfs-3g does (ie. don't use L</guestfs_readlink> on
+NTFS volumes).
+
+Instead if you encounter a symbolic link on an ntfs-3g filesystem, use
+L</guestfs_lgetxattr> to read the C<system.ntfs_reparse_data> extended
+attribute, and read the raw reparse data from that (you can find the
+format documented in various places around the web).
+
+=head3 EXTENDED ATTRIBUTES ON NTFS-3G FILESYSTEMS
+
+There are other useful extended attributes that can be read from
+ntfs-3g filesystems (using L</guestfs_getxattr>). See:
+
+L<http://www.tuxera.com/community/ntfs-3g-advanced/extended-attributes/>
+
=head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
Although we don't want to discourage you from using the C API, we will
mention here that the same API is also available in other languages.
The API is broadly identical in all supported languages. This means
-that the C call C<guestfs_mount(g,path)> is
-C<$g-E<gt>mount($path)> in Perl, C<g.mount(path)> in Python,
-and C<Guestfs.mount g path> in OCaml. In other words, a
+that the C call C<guestfs_add_drive_ro(g,file)> is
+C<$g-E<gt>add_drive_ro($file)> in Perl, C<g.add_drive_ro(file)> in Python,
+and C<g#add_drive_ro file> in OCaml. In other words, a
straightforward, predictable isomorphism between each language.
Error messages are automatically transformed
=item B<OCaml>
-For documentation see the file C<guestfs.mli>.
+See L<guestfs-ocaml(3)>.
=item B<Perl>
-For documentation see L<Sys::Guestfs(3)>.
+See L<guestfs-perl(3)> and L<Sys::Guestfs(3)>.
-=item B<Python>
+=item B<PHP>
-For documentation do:
+For documentation see C<README-PHP> supplied with libguestfs
+sources or in the php-libguestfs package for your distribution.
- $ python
- >>> import guestfs
- >>> help (guestfs)
+The PHP binding only works correctly on 64 bit machines.
+
+=item B<Python>
+
+See L<guestfs-python(3)>.
=item B<Ruby>
-Use the Guestfs module. There is no Ruby-specific documentation, but
-you can find examples written in Ruby in the libguestfs source.
+See L<guestfs-ruby(3)>.
=item B<shell scripts>
-For documentation see L<guestfish(1)>.
+See L<guestfish(1)>.
=back
=item Autosync / forgetting to sync.
+I<Update:> Autosync is enabled by default for all API users starting
+from libguestfs 1.5.24. This section only applies to older versions.
+
When modifying a filesystem from C or another language, you B<must>
unmount all filesystems and call L</guestfs_sync> explicitly before
you close the libguestfs handle. You can also call:
since. Like the Bourne shell, we should have used C<guestfish -c
command> to run commands.
-=back
-
-=head2 PROTOCOL LIMITS
-
-Internally libguestfs uses a message-based protocol to pass API calls
-and their responses to and from a small "appliance" (see L</INTERNALS>
-for plenty more detail about this). The maximum message size used by
-the protocol is slightly less than 4 MB. For some API calls you may
-need to be aware of this limit. The API calls which may be affected
-are individually documented, with a link back to this section of the
-documentation.
-
-A simple call such as L</guestfs_cat> returns its result (the file
-data) in a simple string. Because this string is at some point
-internally encoded as a message, the maximum size that it can return
-is slightly under 4 MB. If the requested file is larger than this
-then you will get an error.
-
-In order to transfer large files into and out of the guest filesystem,
-you need to use particular calls that support this. The sections
-L</UPLOADING> and L</DOWNLOADING> document how to do this.
-
-You might also consider mounting the disk image using our FUSE
-filesystem support (L<guestmount(1)>).
+=item guestfish megabyte modifiers don't work right on all commands
-=head1 CONNECTION MANAGEMENT
+In recent guestfish you can use C<1M> to mean 1 megabyte (and
+similarly for other modifiers). What guestfish actually does is to
+multiply the number part by the modifier part and pass the result to
+the C API. However this doesn't work for a few APIs which aren't
+expecting bytes, but are already expecting some other unit
+(eg. megabytes).
-=head2 guestfs_h *
+The most common is L</guestfs_lvcreate>. The guestfish command:
-C<guestfs_h> is the opaque type representing a connection handle.
-Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
-to free the handle and release all resources used.
+ lvcreate LV VG 100M
-For information on using multiple handles and threads, see the section
-L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
+does not do what you might expect. Instead because
+L</guestfs_lvcreate> is already expecting megabytes, this tries to
+create a 100 I<terabyte> (100 megabytes * megabytes) logical volume.
+The error message you get from this is also a little obscure.
-=head2 guestfs_create
+This could be fixed in the generator by specially marking parameters
+and return values which take bytes or other units.
- guestfs_h *guestfs_create (void);
+=item Ambiguity between devices and paths
-Create a connection handle.
+There is a subtle ambiguity in the API between a device name
+(eg. C</dev/sdb2>) and a similar pathname. A file might just happen
+to be called C<sdb2> in the directory C</dev> (consider some non-Unix
+VM image).
-You have to call L</guestfs_add_drive> on the handle at least once.
+In the current API we usually resolve this ambiguity by having two
+separate calls, for example L</guestfs_checksum> and
+L</guestfs_checksum_device>. Some API calls are ambiguous and
+(incorrectly) resolve the problem by detecting if the path supplied
+begins with C</dev/>.
-This function returns a non-NULL pointer to a handle on success or
-NULL on error.
+To avoid both the ambiguity and the need to duplicate some calls, we
+could make paths/devices into structured names. One way to do this
+would be to use a notation like grub (C<hd(0,0)>), although nobody
+really likes this aspect of grub. Another way would be to use a
+structured type, equivalent to this OCaml type:
-After configuring the handle, you have to call L</guestfs_launch>.
+ type path = Path of string | Device of int | Partition of int * int
-You may also want to configure error handling for the handle. See
-L</ERROR HANDLING> section below.
+which would allow you to pass arguments like:
-=head2 guestfs_close
+ Path "/foo/bar"
+ Device 1 (* /dev/sdb, or perhaps /dev/sda *)
+ Partition (1, 2) (* /dev/sdb2 (or is it /dev/sda2 or /dev/sdb3?) *)
+ Path "/dev/sdb2" (* not a device *)
- void guestfs_close (guestfs_h *g);
+As you can see there are still problems to resolve even with this
+representation. Also consider how it might work in guestfish.
-This closes the connection handle and frees up all resources used.
+=back
-=head1 ERROR HANDLING
+=head2 KEYS AND PASSPHRASES
-The convention in all functions that return C<int> is that they return
-C<-1> to indicate an error. You can get additional information on
-errors by calling L</guestfs_last_error> and/or by setting up an error
-handler with L</guestfs_set_error_handler>.
+Certain libguestfs calls take a parameter that contains sensitive key
+material, passed in as a C string.
-The default error handler prints the information string to C<stderr>.
+In the future we would hope to change the libguestfs implementation so
+that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
+up in swap. However this is I<not> done at the moment, because of the
+complexity of such an implementation.
-Out of memory errors are handled differently. The default action is
-to call L<abort(3)>. If this is undesirable, then you can set a
-handler using L</guestfs_set_out_of_memory_handler>.
+Therefore you should be aware that any key parameter you pass to
+libguestfs might end up being written out to the swap partition. If
+this is a concern, scrub the swap partition or don't use libguestfs on
+encrypted devices.
-=head2 guestfs_last_error
+=head2 MULTIPLE HANDLES AND MULTIPLE THREADS
- const char *guestfs_last_error (guestfs_h *g);
+All high-level libguestfs actions are synchronous. If you want
+to use libguestfs asynchronously then you must create a thread.
-This returns the last error message that happened on C<g>. If
-there has not been an error since the handle was created, then this
-returns C<NULL>.
+Only use the handle from a single thread. Either use the handle
+exclusively from one thread, or provide your own mutex so that two
+threads cannot issue calls on the same handle at the same time.
-The lifetime of the returned string is until the next error occurs, or
-L</guestfs_close> is called.
+See the graphical program guestfs-browser for one possible
+architecture for multithreaded programs using libvirt and libguestfs.
-The error string is not localized (ie. is always in English), because
-this makes searching for error messages in search engines give the
-largest number of results.
+=head2 PATH
-=head2 guestfs_set_error_handler
+Libguestfs needs a supermin appliance, which it finds by looking along
+an internal path.
- typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
- void *data,
- const char *msg);
- void guestfs_set_error_handler (guestfs_h *g,
- guestfs_error_handler_cb cb,
- void *data);
+By default it looks for these in the directory C<$libdir/guestfs>
+(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
-The callback C<cb> will be called if there is an error. The
-parameters passed to the callback are an opaque data pointer and the
-error message string.
+Use L</guestfs_set_path> or set the environment variable
+L</LIBGUESTFS_PATH> to change the directories that libguestfs will
+search in. The value is a colon-separated list of paths. The current
+directory is I<not> searched unless the path contains an empty element
+or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
+search the current directory and then C</usr/lib/guestfs>.
-Note that the message string C<msg> is freed as soon as the callback
-function returns, so if you want to stash it somewhere you must make
-your own copy.
+=head2 QEMU WRAPPERS
-The default handler prints messages on C<stderr>.
+If you want to compile your own qemu, run qemu from a non-standard
+location, or pass extra arguments to qemu, then you can write a
+shell-script wrapper around qemu.
-If you set C<cb> to C<NULL> then I<no> handler is called.
+There is one important rule to remember: you I<must C<exec qemu>> as
+the last command in the shell script (so that qemu replaces the shell
+and becomes the direct child of the libguestfs-using program). If you
+don't do this, then the qemu process won't be cleaned up correctly.
-=head2 guestfs_get_error_handler
+Here is an example of a wrapper, where I have built my own copy of
+qemu from source:
- guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
- void **data_rtn);
+ #!/bin/sh -
+ qemudir=/home/rjones/d/qemu
+ exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
-Returns the current error handler callback.
+Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
+and then use it by setting the LIBGUESTFS_QEMU environment variable.
+For example:
-=head2 guestfs_set_out_of_memory_handler
+ LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
- typedef void (*guestfs_abort_cb) (void);
- int guestfs_set_out_of_memory_handler (guestfs_h *g,
- guestfs_abort_cb);
+Note that libguestfs also calls qemu with the -help and -version
+options in order to determine features.
-The callback C<cb> will be called if there is an out of memory
-situation. I<Note this callback must not return>.
+=head2 ATTACHING TO RUNNING DAEMONS
-The default is to call L<abort(3)>.
+I<Note (1):> This is B<highly experimental> and has a tendency to eat
+babies. Use with caution.
-You cannot set C<cb> to C<NULL>. You can't ignore out of memory
-situations.
+I<Note (2):> This section explains how to attach to a running daemon
+from a low level perspective. For most users, simply using virt tools
+such as L<guestfish(1)> with the I<--live> option will "just work".
-=head2 guestfs_get_out_of_memory_handler
+=head3 Using guestfs_set_attach_method
- guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
+By calling L</guestfs_set_attach_method> you can change how the
+library connects to the C<guestfsd> daemon in L</guestfs_launch>
+(read L</ARCHITECTURE> for some background).
-This returns the current out of memory handler.
+The normal attach method is C<appliance>, where a small appliance is
+created containing the daemon, and then the library connects to this.
-=head1 PATH
+Setting attach method to C<unix:I<path>> (where I<path> is the path of
+a Unix domain socket) causes L</guestfs_launch> to connect to an
+existing daemon over the Unix domain socket.
-Libguestfs needs a kernel and initrd.img, which it finds by looking
-along an internal path.
+The normal use for this is to connect to a running virtual machine
+that contains a C<guestfsd> daemon, and send commands so you can read
+and write files inside the live virtual machine.
-By default it looks for these in the directory C<$libdir/guestfs>
-(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
+=head3 Using guestfs_add_domain with live flag
-Use L</guestfs_set_path> or set the environment variable
-L</LIBGUESTFS_PATH> to change the directories that libguestfs will
-search in. The value is a colon-separated list of paths. The current
-directory is I<not> searched unless the path contains an empty element
-or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
-search the current directory and then C</usr/lib/guestfs>.
+L</guestfs_add_domain> provides some help for getting the
+correct attach method. If you pass the C<live> option to this
+function, then (if the virtual machine is running) it will
+examine the libvirt XML looking for a virtio-serial channel
+to connect to:
-=head1 HIGH-LEVEL API ACTIONS
+ <domain>
+ ...
+ <devices>
+ ...
+ <channel type='unix'>
+ <source mode='bind' path='/path/to/socket'/>
+ <target type='virtio' name='org.libguestfs.channel.0'/>
+ </channel>
+ ...
+ </devices>
+ </domain>
+
+L</guestfs_add_domain> extracts C</path/to/socket> and sets the attach
+method to C<unix:/path/to/socket>.
+
+Some of the libguestfs tools (including guestfish) support a I<--live>
+option which is passed through to L</guestfs_add_domain> thus allowing
+you to attach to and modify live virtual machines.
+
+The virtual machine needs to have been set up beforehand so that it
+has the virtio-serial channel and so that guestfsd is running inside
+it.
=head2 ABI GUARANTEE
calls, we will keep the old actions forever. This allows you the
developer to program in confidence against the libguestfs API.
-@ACTIONS@
+=head2 BLOCK DEVICE NAMING
-=head1 STRUCTURES
+In the kernel there is now quite a profusion of schemata for naming
+block devices (in this context, by I<block device> I mean a physical
+or virtual hard drive). The original Linux IDE driver used names
+starting with C</dev/hd*>. SCSI devices have historically used a
+different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
+driver became a popular replacement for the old IDE driver
+(particularly for SATA devices) those devices also used the
+C</dev/sd*> scheme. Additionally we now have virtual machines with
+paravirtualized drivers. This has created several different naming
+systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
+PV disks.
-@STRUCTS@
+As discussed above, libguestfs uses a qemu appliance running an
+embedded Linux kernel to access block devices. We can run a variety
+of appliances based on a variety of Linux kernels.
-=head1 AVAILABILITY
+This causes a problem for libguestfs because many API calls use device
+or partition names. Working scripts and the recipe (example) scripts
+that we make available over the internet could fail if the naming
+scheme changes.
-=head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
+Therefore libguestfs defines C</dev/sd*> as the I<standard naming
+scheme>. Internally C</dev/sd*> names are translated, if necessary,
+to other names as required. For example, under RHEL 5 which uses the
+C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
+C</dev/hda2> transparently.
-Using L</guestfs_available> you can test availability of
-the following groups of functions. This test queries the
-appliance to see if the appliance you are currently using
-supports the functionality.
+Note that this I<only> applies to parameters. The
+L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
+return the true names of the devices and partitions as known to the
+appliance.
-@AVAILABILITY@
+=head3 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
-=head2 SINGLE CALLS AT COMPILE TIME
+Usually this translation is transparent. However in some (very rare)
+cases you may need to know the exact algorithm. Such cases include
+where you use L</guestfs_config> to add a mixture of virtio and IDE
+devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
+and C</dev/vd*> devices.
-If you need to test whether a single libguestfs function is
-available at compile time, we recommend using build tools
-such as autoconf or cmake. For example in autotools you could
-use:
+The algorithm is applied only to I<parameters> which are known to be
+either device or partition names. Return values from functions such
+as L</guestfs_list_devices> are never changed.
- AC_CHECK_LIB([guestfs],[guestfs_create])
- AC_CHECK_FUNCS([guestfs_dd])
+=over 4
-which would result in C<HAVE_GUESTFS_DD> being either defined
-or not defined in your program.
+=item *
-=head2 SINGLE CALLS AT RUN TIME
+Is the string a parameter which is a device or partition name?
-Testing at compile time doesn't guarantee that a function really
-exists in the library. The reason is that you might be dynamically
-linked against a previous I<libguestfs.so> (dynamic library)
-which doesn't have the call. This situation unfortunately results
-in a segmentation fault, which is a shortcoming of the C dynamic
-linking system itself.
+=item *
-You can use L<dlopen(3)> to test if a function is available
-at run time, as in this example program (note that you still
-need the compile time check as well):
+Does the string begin with C</dev/sd>?
- #include <config.h>
-
- #include <stdio.h>
- #include <stdlib.h>
- #include <unistd.h>
- #include <dlfcn.h>
- #include <guestfs.h>
-
- main ()
- {
- #ifdef HAVE_GUESTFS_DD
- void *dl;
- int has_function;
-
- /* Test if the function guestfs_dd is really available. */
- dl = dlopen (NULL, RTLD_LAZY);
- if (!dl) {
- fprintf (stderr, "dlopen: %s\n", dlerror ());
- exit (EXIT_FAILURE);
- }
- has_function = dlsym (dl, "guestfs_dd") != NULL;
- dlclose (dl);
-
- if (!has_function)
- printf ("this libguestfs.so does NOT have guestfs_dd function\n");
- else {
- printf ("this libguestfs.so has guestfs_dd function\n");
- /* Now it's safe to call
- guestfs_dd (g, "foo", "bar");
- */
- }
- #else
- printf ("guestfs_dd function was not found at compile time\n");
- #endif
- }
+=item *
-You may think the above is an awful lot of hassle, and it is.
-There are other ways outside of the C linking system to ensure
-that this kind of incompatibility never arises, such as using
+Does the named device exist? If so, we use that device.
+However if I<not> then we continue with this algorithm.
+
+=item *
+
+Replace initial C</dev/sd> string with C</dev/hd>.
+
+For example, change C</dev/sda2> to C</dev/hda2>.
+
+If that named device exists, use it. If not, continue.
+
+=item *
+
+Replace initial C</dev/sd> string with C</dev/vd>.
+
+If that named device exists, use it. If not, return an error.
+
+=back
+
+=head3 PORTABILITY CONCERNS WITH BLOCK DEVICE NAMING
+
+Although the standard naming scheme and automatic translation is
+useful for simple programs and guestfish scripts, for larger programs
+it is best not to rely on this mechanism.
+
+Where possible for maximum future portability programs using
+libguestfs should use these future-proof techniques:
+
+=over 4
+
+=item *
+
+Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
+actual device names, and then use those names directly.
+
+Since those device names exist by definition, they will never be
+translated.
+
+=item *
+
+Use higher level ways to identify filesystems, such as LVM names,
+UUIDs and filesystem labels.
+
+=back
+
+=head1 SECURITY
+
+This section discusses security implications of using libguestfs,
+particularly with untrusted or malicious guests or disk images.
+
+=head2 GENERAL SECURITY CONSIDERATIONS
+
+Be careful with any files or data that you download from a guest (by
+"download" we mean not just the L</guestfs_download> command but any
+command that reads files, filenames, directories or anything else from
+a disk image). An attacker could manipulate the data to fool your
+program into doing the wrong thing. Consider cases such as:
+
+=over 4
+
+=item *
+
+the data (file etc) not being present
+
+=item *
+
+being present but empty
+
+=item *
+
+being much larger than normal
+
+=item *
+
+containing arbitrary 8 bit data
+
+=item *
+
+being in an unexpected character encoding
+
+=item *
+
+containing homoglyphs.
+
+=back
+
+=head2 SECURITY OF MOUNTING FILESYSTEMS
+
+When you mount a filesystem under Linux, mistakes in the kernel
+filesystem (VFS) module can sometimes be escalated into exploits by
+deliberately creating a malicious, malformed filesystem. These
+exploits are very severe for two reasons. Firstly there are very many
+filesystem drivers in the kernel, and many of them are infrequently
+used and not much developer attention has been paid to the code.
+Linux userspace helps potential crackers by detecting the filesystem
+type and automatically choosing the right VFS driver, even if that
+filesystem type is obscure or unexpected for the administrator.
+Secondly, a kernel-level exploit is like a local root exploit (worse
+in some ways), giving immediate and total access to the system right
+down to the hardware level.
+
+That explains why you should never mount a filesystem from an
+untrusted guest on your host kernel. How about libguestfs? We run a
+Linux kernel inside a qemu virtual machine, usually running as a
+non-root user. The attacker would need to write a filesystem which
+first exploited the kernel, and then exploited either qemu
+virtualization (eg. a faulty qemu driver) or the libguestfs protocol,
+and finally to be as serious as the host kernel exploit it would need
+to escalate its privileges to root. This multi-step escalation,
+performed by a static piece of data, is thought to be extremely hard
+to do, although we never say 'never' about security issues.
+
+In any case callers can reduce the attack surface by forcing the
+filesystem type when mounting (use L</guestfs_mount_vfs>).
+
+=head2 PROTOCOL SECURITY
+
+The protocol is designed to be secure, being based on RFC 4506 (XDR)
+with a defined upper message size. However a program that uses
+libguestfs must also take care - for example you can write a program
+that downloads a binary from a disk image and executes it locally, and
+no amount of protocol security will save you from the consequences.
+
+=head2 INSPECTION SECURITY
+
+Parts of the inspection API (see L</INSPECTION>) return untrusted
+strings directly from the guest, and these could contain any 8 bit
+data. Callers should be careful to escape these before printing them
+to a structured file (for example, use HTML escaping if creating a web
+page).
+
+Guest configuration may be altered in unusual ways by the
+administrator of the virtual machine, and may not reflect reality
+(particularly for untrusted or actively malicious guests). For
+example we parse the hostname from configuration files like
+C</etc/sysconfig/network> that we find in the guest, but the guest
+administrator can easily manipulate these files to provide the wrong
+hostname.
+
+The inspection API parses guest configuration using two external
+libraries: Augeas (Linux configuration) and hivex (Windows Registry).
+Both are designed to be robust in the face of malicious data, although
+denial of service attacks are still possible, for example with
+oversized configuration files.
+
+=head2 RUNNING UNTRUSTED GUEST COMMANDS
+
+Be very cautious about running commands from the guest. By running a
+command in the guest, you are giving CPU time to a binary that you do
+not control, under the same user account as the library, albeit
+wrapped in qemu virtualization. More information and alternatives can
+be found in the section L</RUNNING COMMANDS>.
+
+=head2 CVE-2010-3851
+
+https://bugzilla.redhat.com/642934
+
+This security bug concerns the automatic disk format detection that
+qemu does on disk images.
+
+A raw disk image is just the raw bytes, there is no header. Other
+disk images like qcow2 contain a special header. Qemu deals with this
+by looking for one of the known headers, and if none is found then
+assuming the disk image must be raw.
+
+This allows a guest which has been given a raw disk image to write
+some other header. At next boot (or when the disk image is accessed
+by libguestfs) qemu would do autodetection and think the disk image
+format was, say, qcow2 based on the header written by the guest.
+
+This in itself would not be a problem, but qcow2 offers many features,
+one of which is to allow a disk image to refer to another image
+(called the "backing disk"). It does this by placing the path to the
+backing disk into the qcow2 header. This path is not validated and
+could point to any host file (eg. "/etc/passwd"). The backing disk is
+then exposed through "holes" in the qcow2 disk image, which of course
+is completely under the control of the attacker.
+
+In libguestfs this is rather hard to exploit except under two
+circumstances:
+
+=over 4
+
+=item 1.
+
+You have enabled the network or have opened the disk in write mode.
+
+=item 2.
+
+You are also running untrusted code from the guest (see
+L</RUNNING COMMANDS>).
+
+=back
+
+The way to avoid this is to specify the expected disk format when
+adding disks (the optional C<format> option to
+L</guestfs_add_drive_opts>). You should always do this if the disk is
+raw format, and it's a good idea for other cases too.
+
+For disks added from libvirt using calls like L</guestfs_add_domain>,
+the format is fetched from libvirt and passed through.
+
+For libguestfs tools, use the I<--format> command line parameter as
+appropriate.
+
+=head1 CONNECTION MANAGEMENT
+
+=head2 guestfs_h *
+
+C<guestfs_h> is the opaque type representing a connection handle.
+Create a handle by calling L</guestfs_create>. Call L</guestfs_close>
+to free the handle and release all resources used.
+
+For information on using multiple handles and threads, see the section
+L</MULTIPLE HANDLES AND MULTIPLE THREADS> above.
+
+=head2 guestfs_create
+
+ guestfs_h *guestfs_create (void);
+
+Create a connection handle.
+
+On success this returns a non-NULL pointer to a handle. On error it
+returns NULL.
+
+You have to "configure" the handle after creating it. This includes
+calling L</guestfs_add_drive_opts> (or one of the equivalent calls) on
+the handle at least once.
+
+After configuring the handle, you have to call L</guestfs_launch>.
+
+You may also want to configure error handling for the handle. See the
+L</ERROR HANDLING> section below.
+
+=head2 guestfs_close
+
+ void guestfs_close (guestfs_h *g);
+
+This closes the connection handle and frees up all resources used.
+
+If autosync was set on the handle and the handle was launched, then
+this implicitly calls various functions to unmount filesystems and
+sync the disk. See L</guestfs_set_autosync> for more details.
+
+If a close callback was set on the handle, then it is called.
+
+=head1 ERROR HANDLING
+
+API functions can return errors. For example, almost all functions
+that return C<int> will return C<-1> to indicate an error.
+
+Additional information is available for errors: an error message
+string and optionally an error number (errno) if the thing that failed
+was a system call.
+
+You can get at the additional information about the last error on the
+handle by calling L</guestfs_last_error>, L</guestfs_last_errno>,
+and/or by setting up an error handler with
+L</guestfs_set_error_handler>.
+
+When the handle is created, a default error handler is installed which
+prints the error message string to C<stderr>. For small short-running
+command line programs it is sufficient to do:
+
+ if (guestfs_launch (g) == -1)
+ exit (EXIT_FAILURE);
+
+since the default error handler will ensure that an error message has
+been printed to C<stderr> before the program exits.
+
+For other programs the caller will almost certainly want to install an
+alternate error handler or do error handling in-line like this:
+
+ g = guestfs_create ();
+
+ /* This disables the default behaviour of printing errors
+ on stderr. */
+ guestfs_set_error_handler (g, NULL, NULL);
+
+ if (guestfs_launch (g) == -1) {
+ /* Examine the error message and print it etc. */
+ char *msg = guestfs_last_error (g);
+ int errnum = guestfs_last_errno (g);
+ fprintf (stderr, "%s\n", msg);
+ /* ... */
+ }
+
+Out of memory errors are handled differently. The default action is
+to call L<abort(3)>. If this is undesirable, then you can set a
+handler using L</guestfs_set_out_of_memory_handler>.
+
+L</guestfs_create> returns C<NULL> if the handle cannot be created,
+and because there is no handle if this happens there is no way to get
+additional error information. However L</guestfs_create> is supposed
+to be a lightweight operation which can only fail because of
+insufficient memory (it returns NULL in this case).
+
+=head2 guestfs_last_error
+
+ const char *guestfs_last_error (guestfs_h *g);
+
+This returns the last error message that happened on C<g>. If
+there has not been an error since the handle was created, then this
+returns C<NULL>.
+
+The lifetime of the returned string is until the next error occurs, or
+L</guestfs_close> is called.
+
+=head2 guestfs_last_errno
+
+ int guestfs_last_errno (guestfs_h *g);
+
+This returns the last error number (errno) that happened on C<g>.
+
+If successful, an errno integer not equal to zero is returned.
+
+If no error, this returns 0. This call can return 0 in three
+situations:
+
+=over 4
+
+=item 1.
+
+There has not been any error on the handle.
+
+=item 2.
+
+There has been an error but the errno was meaningless. This
+corresponds to the case where the error did not come from a
+failed system call, but for some other reason.
+
+=item 3.
+
+There was an error from a failed system call, but for some
+reason the errno was not captured and returned. This usually
+indicates a bug in libguestfs.
+
+=back
+
+Libguestfs tries to convert the errno from inside the applicance into
+a corresponding errno for the caller (not entirely trivial: the
+appliance might be running a completely different operating system
+from the library and error numbers are not standardized across
+Un*xen). If this could not be done, then the error is translated to
+C<EINVAL>. In practice this should only happen in very rare
+circumstances.
+
+=head2 guestfs_set_error_handler
+
+ typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
+ void *opaque,
+ const char *msg);
+ void guestfs_set_error_handler (guestfs_h *g,
+ guestfs_error_handler_cb cb,
+ void *opaque);
+
+The callback C<cb> will be called if there is an error. The
+parameters passed to the callback are an opaque data pointer and the
+error message string.
+
+C<errno> is not passed to the callback. To get that the callback must
+call L</guestfs_last_errno>.
+
+Note that the message string C<msg> is freed as soon as the callback
+function returns, so if you want to stash it somewhere you must make
+your own copy.
+
+The default handler prints messages on C<stderr>.
+
+If you set C<cb> to C<NULL> then I<no> handler is called.
+
+=head2 guestfs_get_error_handler
+
+ guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
+ void **opaque_rtn);
+
+Returns the current error handler callback.
+
+=head2 guestfs_set_out_of_memory_handler
+
+ typedef void (*guestfs_abort_cb) (void);
+ int guestfs_set_out_of_memory_handler (guestfs_h *g,
+ guestfs_abort_cb);
+
+The callback C<cb> will be called if there is an out of memory
+situation. I<Note this callback must not return>.
+
+The default is to call L<abort(3)>.
+
+You cannot set C<cb> to C<NULL>. You can't ignore out of memory
+situations.
+
+=head2 guestfs_get_out_of_memory_handler
+
+ guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);
+
+This returns the current out of memory handler.
+
+=head1 API CALLS
+
+@ACTIONS@
+
+=head1 STRUCTURES
+
+@STRUCTS@
+
+=head1 AVAILABILITY
+
+=head2 GROUPS OF FUNCTIONALITY IN THE APPLIANCE
+
+Using L</guestfs_available> you can test availability of
+the following groups of functions. This test queries the
+appliance to see if the appliance you are currently using
+supports the functionality.
+
+@AVAILABILITY@
+
+=head2 GUESTFISH supported COMMAND
+
+In L<guestfish(3)> there is a handy interactive command
+C<supported> which prints out the available groups and
+whether they are supported by this build of libguestfs.
+Note however that you have to do C<run> first.
+
+=head2 SINGLE CALLS AT COMPILE TIME
+
+Since version 1.5.8, C<E<lt>guestfs.hE<gt>> defines symbols
+for each C API function, such as:
+
+ #define LIBGUESTFS_HAVE_DD 1
+
+if L</guestfs_dd> is available.
+
+Before version 1.5.8, if you needed to test whether a single
+libguestfs function is available at compile time, we recommended using
+build tools such as autoconf or cmake. For example in autotools you
+could use:
+
+ AC_CHECK_LIB([guestfs],[guestfs_create])
+ AC_CHECK_FUNCS([guestfs_dd])
+
+which would result in C<HAVE_GUESTFS_DD> being either defined
+or not defined in your program.
+
+=head2 SINGLE CALLS AT RUN TIME
+
+Testing at compile time doesn't guarantee that a function really
+exists in the library. The reason is that you might be dynamically
+linked against a previous I<libguestfs.so> (dynamic library)
+which doesn't have the call. This situation unfortunately results
+in a segmentation fault, which is a shortcoming of the C dynamic
+linking system itself.
+
+You can use L<dlopen(3)> to test if a function is available
+at run time, as in this example program (note that you still
+need the compile time check as well):
+
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <unistd.h>
+ #include <dlfcn.h>
+ #include <guestfs.h>
+
+ main ()
+ {
+ #ifdef LIBGUESTFS_HAVE_DD
+ void *dl;
+ int has_function;
+
+ /* Test if the function guestfs_dd is really available. */
+ dl = dlopen (NULL, RTLD_LAZY);
+ if (!dl) {
+ fprintf (stderr, "dlopen: %s\n", dlerror ());
+ exit (EXIT_FAILURE);
+ }
+ has_function = dlsym (dl, "guestfs_dd") != NULL;
+ dlclose (dl);
+
+ if (!has_function)
+ printf ("this libguestfs.so does NOT have guestfs_dd function\n");
+ else {
+ printf ("this libguestfs.so has guestfs_dd function\n");
+ /* Now it's safe to call
+ guestfs_dd (g, "foo", "bar");
+ */
+ }
+ #else
+ printf ("guestfs_dd function was not found at compile time\n");
+ #endif
+ }
+
+You may think the above is an awful lot of hassle, and it is.
+There are other ways outside of the C linking system to ensure
+that this kind of incompatibility never arises, such as using
package versioning:
- Requires: libguestfs >= 1.0.80
+ Requires: libguestfs >= 1.0.80
+
+=head1 CALLS WITH OPTIONAL ARGUMENTS
+
+A recent feature of the API is the introduction of calls which take
+optional arguments. In C these are declared 3 ways. The main way is
+as a call which takes variable arguments (ie. C<...>), as in this
+example:
+
+ int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
+
+Call this with a list of optional arguments, terminated by C<-1>.
+So to call with no optional arguments specified:
+
+ guestfs_add_drive_opts (g, filename, -1);
+
+With a single optional argument:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ -1);
+
+With two:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+ -1);
+
+and so forth. Don't forget the terminating C<-1> otherwise
+Bad Things will happen!
+
+=head2 USING va_list FOR OPTIONAL ARGUMENTS
+
+The second variant has the same name with the suffix C<_va>, which
+works the same way but takes a C<va_list>. See the C manual for
+details. For the example function, this is declared:
+
+ int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
+ va_list args);
+
+=head2 CONSTRUCTING OPTIONAL ARGUMENTS
+
+The third variant is useful where you need to construct these
+calls. You pass in a structure where you fill in the optional
+fields. The structure has a bitmask as the first element which
+you must set to indicate which fields you have filled in. For
+our example function the structure and call are declared:
+
+ struct guestfs_add_drive_opts_argv {
+ uint64_t bitmask;
+ int readonly;
+ const char *format;
+ /* ... */
+ };
+ int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
+ const struct guestfs_add_drive_opts_argv *optargs);
+
+You could call it like this:
+
+ struct guestfs_add_drive_opts_argv optargs = {
+ .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
+ .readonly = 1,
+ .format = "qcow2"
+ };
+
+ guestfs_add_drive_opts_argv (g, filename, &optargs);
+
+Notes:
+
+=over 4
+
+=item *
+
+The C<_BITMASK> suffix on each option name when specifying the
+bitmask.
+
+=item *
+
+You do not need to fill in all fields of the structure.
+
+=item *
+
+There must be a one-to-one correspondence between fields of the
+structure that are filled in, and bits set in the bitmask.
-=begin html
+=back
-<!-- old anchor for the next section -->
-<a name="state_machine_and_low_level_event_api"/>
+=head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES
-=end html
+In other languages, optional arguments are expressed in the
+way that is natural for that language. We refer you to the
+language-specific documentation for more details on that.
-=head1 ARCHITECTURE
+For guestfish, see L<guestfish(1)/OPTIONAL ARGUMENTS>.
-Internally, libguestfs is implemented by running an appliance (a
-special type of small virtual machine) using L<qemu(1)>. Qemu runs as
-a child process of the main program.
+=head2 SETTING CALLBACKS TO HANDLE EVENTS
- ___________________
- / \
- | main program |
- | |
- | | child process / appliance
- | | __________________________
- | | / qemu \
- +-------------------+ RPC | +-----------------+ |
- | libguestfs <--------------------> guestfsd | |
- | | | +-----------------+ |
- \___________________/ | | Linux kernel | |
- | +--^--------------+ |
- \_________|________________/
- |
- _______v______
- / \
- | Device or |
- | disk image |
- \______________/
+B<Note:> This section documents the generic event mechanism introduced
+in libguestfs 1.10, which you should use in new code if possible. The
+old functions C<guestfs_set_log_message_callback>,
+C<guestfs_set_subprocess_quit_callback>,
+C<guestfs_set_launch_done_callback>, C<guestfs_set_close_callback> and
+C<guestfs_set_progress_callback> are no longer documented in this
+manual page. Because of the ABI guarantee, the old functions continue
+to work.
+
+Handles generate events when certain things happen, such as log
+messages being generated, progress messages during long-running
+operations, or the handle being closed. The API calls described below
+let you register a callback to be called when events happen. You can
+register multiple callbacks (for the same, different or overlapping
+sets of events), and individually remove callbacks. If callbacks are
+not removed, then they remain in force until the handle is closed.
+
+In the current implementation, events are only generated
+synchronously: that means that events (and hence callbacks) can only
+happen while you are in the middle of making another libguestfs call.
+The callback is called in the same thread.
+
+Events may contain a payload, usually nothing (void), an array of 64
+bit unsigned integers, or a message buffer. Payloads are discussed
+later on.
+
+=head3 CLASSES OF EVENTS
-The library, linked to the main program, creates the child process and
-hence the appliance in the L</guestfs_launch> function.
+=over 4
-Inside the appliance is a Linux kernel and a complete stack of
-userspace tools (such as LVM and ext2 programs) and a small
-controlling daemon called L</guestfsd>. The library talks to
-L</guestfsd> using remote procedure calls (RPC). There is a mostly
-one-to-one correspondence between libguestfs API calls and RPC calls
-to the daemon. Lastly the disk image(s) are attached to the qemu
-process which translates device access by the appliance's Linux kernel
-into accesses to the image.
+=item GUESTFS_EVENT_CLOSE
+(payload type: void)
-A common misunderstanding is that the appliance "is" the virtual
-machine. Although the disk image you are attached to might also be
-used by some virtual machine, libguestfs doesn't know or care about
-this. (But you will care if both libguestfs's qemu process and your
-virtual machine are trying to update the disk image at the same time,
-since these usually results in massive disk corruption).
+The callback function will be called while the handle is being closed
+(synchronously from L</guestfs_close>).
-=head1 STATE MACHINE
+Note that libguestfs installs an L<atexit(3)> handler to try to clean
+up handles that are open when the program exits. This means that this
+callback might be called indirectly from L<exit(3)>, which can cause
+unexpected problems in higher-level languages (eg. if your HLL
+interpreter has already been cleaned up by the time this is called,
+and if your callback then jumps into some HLL function).
-libguestfs uses a state machine to model the child process:
+If no callback is registered: the handle is closed without any
+callback being invoked.
- |
- guestfs_create
- |
- |
- ____V_____
- / \
- | CONFIG |
- \__________/
- ^ ^ ^ \
- / | \ \ guestfs_launch
- / | _\__V______
- / | / \
- / | | LAUNCHING |
- / | \___________/
- / | /
- / | guestfs_launch
- / | /
- ______ / __|____V
- / \ ------> / \
- | BUSY | | READY |
- \______/ <------ \________/
+=item GUESTFS_EVENT_SUBPROCESS_QUIT
+(payload type: void)
-The normal transitions are (1) CONFIG (when the handle is created, but
-there is no child process), (2) LAUNCHING (when the child process is
-booting up), (3) alternating between READY and BUSY as commands are
-issued to, and carried out by, the child process.
+The callback function will be called when the child process quits,
+either asynchronously or if killed by L</guestfs_kill_subprocess>.
+(This corresponds to a transition from any state to the CONFIG state).
-The guest may be killed by L</guestfs_kill_subprocess>, or may die
-asynchronously at any time (eg. due to some internal error), and that
-causes the state to transition back to CONFIG.
+If no callback is registered: the event is ignored.
-Configuration commands for qemu such as L</guestfs_add_drive> can only
-be issued when in the CONFIG state.
+=item GUESTFS_EVENT_LAUNCH_DONE
+(payload type: void)
-The high-level API offers two calls that go from CONFIG through
-LAUNCHING to READY. L</guestfs_launch> blocks until the child process
-is READY to accept commands (or until some failure or timeout).
-L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
-while it is running.
+The callback function will be called when the child process becomes
+ready first time after it has been launched. (This corresponds to a
+transition from LAUNCHING to the READY state).
-High-level API actions such as L</guestfs_mount> can only be issued
-when in the READY state. These high-level API calls block waiting for
-the command to be carried out (ie. the state to transition to BUSY and
-then back to READY). But using the low-level event API, you get
-non-blocking versions. (But you can still only carry out one
-operation per handle at a time - that is a limitation of the
-communications protocol we use).
+If no callback is registered: the event is ignored.
-Finally, the child process sends asynchronous messages back to the
-main program, such as kernel log messages. Mostly these are ignored
-by the high-level API, but using the low-level event API you can
-register to receive these messages.
+=item GUESTFS_EVENT_PROGRESS
+(payload type: array of 4 x uint64_t)
-=head2 SETTING CALLBACKS TO HANDLE EVENTS
+Some long-running operations can generate progress messages. If
+this callback is registered, then it will be called each time a
+progress message is generated (usually two seconds after the
+operation started, and three times per second thereafter until
+it completes, although the frequency may change in future versions).
-The child process generates events in some situations. Current events
-include: receiving a log message, the child process exits.
+The callback receives in the payload four unsigned 64 bit numbers
+which are (in order): C<proc_nr>, C<serial>, C<position>, C<total>.
-Use the C<guestfs_set_*_callback> functions to set a callback for
-different types of events.
+The units of C<total> are not defined, although for some
+operations C<total> may relate in some way to the amount of
+data to be transferred (eg. in bytes or megabytes), and
+C<position> may be the portion which has been transferred.
-Only I<one callback of each type> can be registered for each handle.
-Calling C<guestfs_set_*_callback> again overwrites the previous
-callback of that type. Cancel all callbacks of this type by calling
-this function with C<cb> set to C<NULL>.
+The only defined and stable parts of the API are:
-=head2 guestfs_set_log_message_callback
+=over 4
- typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
- char *buf, int len);
- void guestfs_set_log_message_callback (guestfs_h *g,
- guestfs_log_message_cb cb,
- void *opaque);
+=item *
-The callback function C<cb> will be called whenever qemu or the guest
-writes anything to the console.
+The callback can display to the user some type of progress bar or
+indicator which shows the ratio of C<position>:C<total>.
-Use this function to capture kernel messages and similar.
+=item *
-Normally there is no log message handler, and log messages are just
-discarded.
+0 E<lt>= C<position> E<lt>= C<total>
-=head2 guestfs_set_subprocess_quit_callback
+=item *
- typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
- void guestfs_set_subprocess_quit_callback (guestfs_h *g,
- guestfs_subprocess_quit_cb cb,
- void *opaque);
+If any progress notification is sent during a call, then a final
+progress notification is always sent when C<position> = C<total>
+(I<unless> the call fails with an error).
-The callback function C<cb> will be called when the child process
-quits, either asynchronously or if killed by
-L</guestfs_kill_subprocess>. (This corresponds to a transition from
-any state to the CONFIG state).
+This is to simplify caller code, so callers can easily set the
+progress indicator to "100%" at the end of the operation, without
+requiring special code to detect this case.
-=head2 guestfs_set_launch_done_callback
+=item *
- typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
- void guestfs_set_launch_done_callback (guestfs_h *g,
- guestfs_ready_cb cb,
- void *opaque);
+For some calls we are unable to estimate the progress of the call, but
+we can still generate progress messages to indicate activity. This is
+known as "pulse mode", and is directly supported by certain progress
+bar implementations (eg. GtkProgressBar).
-The callback function C<cb> will be called when the child process
-becomes ready first time after it has been launched. (This
-corresponds to a transition from LAUNCHING to the READY state).
+For these calls, zero or more progress messages are generated with
+C<position = 0> and C<total = 1>, followed by a final message with
+C<position = total = 1>.
-=head1 BLOCK DEVICE NAMING
+As noted above, if the call fails with an error then the final message
+may not be generated.
-In the kernel there is now quite a profusion of schemata for naming
-block devices (in this context, by I<block device> I mean a physical
-or virtual hard drive). The original Linux IDE driver used names
-starting with C</dev/hd*>. SCSI devices have historically used a
-different naming scheme, C</dev/sd*>. When the Linux kernel I<libata>
-driver became a popular replacement for the old IDE driver
-(particularly for SATA devices) those devices also used the
-C</dev/sd*> scheme. Additionally we now have virtual machines with
-paravirtualized drivers. This has created several different naming
-systems, such as C</dev/vd*> for virtio disks and C</dev/xvd*> for Xen
-PV disks.
+=back
-As discussed above, libguestfs uses a qemu appliance running an
-embedded Linux kernel to access block devices. We can run a variety
-of appliances based on a variety of Linux kernels.
+The callback also receives the procedure number (C<proc_nr>) and
+serial number (C<serial>) of the call. These are only useful for
+debugging protocol issues, and the callback can normally ignore them.
+The callback may want to print these numbers in error messages or
+debugging messages.
-This causes a problem for libguestfs because many API calls use device
-or partition names. Working scripts and the recipe (example) scripts
-that we make available over the internet could fail if the naming
-scheme changes.
+If no callback is registered: progress messages are discarded.
-Therefore libguestfs defines C</dev/sd*> as the I<standard naming
-scheme>. Internally C</dev/sd*> names are translated, if necessary,
-to other names as required. For example, under RHEL 5 which uses the
-C</dev/hd*> scheme, any device parameter C</dev/sda2> is translated to
-C</dev/hda2> transparently.
+=item GUESTFS_EVENT_APPLIANCE
+(payload type: message buffer)
-Note that this I<only> applies to parameters. The
-L</guestfs_list_devices>, L</guestfs_list_partitions> and similar calls
-return the true names of the devices and partitions as known to the
-appliance.
+The callback function is called whenever a log message is generated by
+qemu, the appliance kernel, guestfsd (daemon), or utility programs.
-=head2 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
+If the verbose flag (L</guestfs_set_verbose>) is set before launch
+(L</guestfs_launch>) then additional debug messages are generated.
-Usually this translation is transparent. However in some (very rare)
-cases you may need to know the exact algorithm. Such cases include
-where you use L</guestfs_config> to add a mixture of virtio and IDE
-devices to the qemu-based appliance, so have a mixture of C</dev/sd*>
-and C</dev/vd*> devices.
+If no callback is registered: the messages are discarded unless the
+verbose flag is set in which case they are sent to stderr. You can
+override the printing of verbose messages to stderr by setting up a
+callback.
-The algorithm is applied only to I<parameters> which are known to be
-either device or partition names. Return values from functions such
-as L</guestfs_list_devices> are never changed.
+=item GUESTFS_EVENT_LIBRARY
+(payload type: message buffer)
+
+The callback function is called whenever a log message is generated by
+the library part of libguestfs.
+
+If the verbose flag (L</guestfs_set_verbose>) is set then additional
+debug messages are generated.
+
+If no callback is registered: the messages are discarded unless the
+verbose flag is set in which case they are sent to stderr. You can
+override the printing of verbose messages to stderr by setting up a
+callback.
+
+=item GUESTFS_EVENT_TRACE
+(payload type: message buffer)
+
+The callback function is called whenever a trace message is generated.
+This only applies if the trace flag (L</guestfs_set_trace>) is set.
+
+If no callback is registered: the messages are sent to stderr. You
+can override the printing of trace messages to stderr by setting up a
+callback.
+
+=back
+
+=head3 guestfs_set_event_callback
+
+ int guestfs_set_event_callback (guestfs_h *g,
+ guestfs_event_callback cb,
+ uint64_t event_bitmask,
+ int flags,
+ void *opaque);
+
+This function registers a callback (C<cb>) for all event classes
+in the C<event_bitmask>.
+
+For example, to register for all log message events, you could call
+this function with the bitmask
+C<GUESTFS_EVENT_APPLIANCE|GUESTFS_EVENT_LIBRARY>. To register a
+single callback for all possible classes of events, use
+C<GUESTFS_EVENT_ALL>.
+
+C<flags> should always be passed as 0.
+
+C<opaque> is an opaque pointer which is passed to the callback. You
+can use it for any purpose.
+
+The return value is the event handle (an integer) which you can use to
+delete the callback (see below).
+
+If there is an error, this function returns C<-1>, and sets the error
+in the handle in the usual way (see L</guestfs_last_error> etc.)
+
+Callbacks remain in effect until they are deleted, or until the handle
+is closed.
+
+In the case where multiple callbacks are registered for a particular
+event class, all of the callbacks are called. The order in which
+multiple callbacks are called is not defined.
+
+=head3 guestfs_delete_event_callback
+
+ void guestfs_delete_event_callback (guestfs_h *g, int event_handle);
+
+Delete a callback that was previously registered. C<event_handle>
+should be the integer that was returned by a previous call to
+C<guestfs_set_event_callback> on the same handle.
+
+=head3 guestfs_event_callback
+
+ typedef void (*guestfs_event_callback) (
+ guestfs_h *g,
+ void *opaque,
+ uint64_t event,
+ int event_handle,
+ int flags,
+ const char *buf, size_t buf_len,
+ const uint64_t *array, size_t array_len);
+
+This is the type of the event callback function that you have to
+provide.
+
+The basic parameters are: the handle (C<g>), the opaque user pointer
+(C<opaque>), the event class (eg. C<GUESTFS_EVENT_PROGRESS>), the
+event handle, and C<flags> which in the current API you should ignore.
+
+The remaining parameters contain the event payload (if any). Each
+event may contain a payload, which usually relates to the event class,
+but for future proofing your code should be written to handle any
+payload for any event class.
+
+C<buf> and C<buf_len> contain a message buffer (if C<buf_len == 0>,
+then there is no message buffer). Note that this message buffer can
+contain arbitrary 8 bit data, including NUL bytes.
+
+C<array> and C<array_len> is an array of 64 bit unsigned integers. At
+the moment this is only used for progress messages.
+
+=head3 EXAMPLE: CAPTURING LOG MESSAGES
+
+One motivation for the generic event API was to allow GUI programs to
+capture debug and other messages. In libguestfs E<le> 1.8 these were
+sent unconditionally to C<stderr>.
+
+Events associated with log messages are: C<GUESTFS_EVENT_LIBRARY>,
+C<GUESTFS_EVENT_APPLIANCE> and C<GUESTFS_EVENT_TRACE>. (Note that
+error messages are not events; you must capture error messages
+separately).
+
+Programs have to set up a callback to capture the classes of events of
+interest:
+
+ int eh =
+ guestfs_set_event_callback
+ (g, message_callback,
+ GUESTFS_EVENT_LIBRARY|GUESTFS_EVENT_APPLIANCE|
+ GUESTFS_EVENT_TRACE,
+ 0, NULL) == -1)
+ if (eh == -1) {
+ // handle error in the usual way
+ }
+
+The callback can then direct messages to the appropriate place. In
+this example, messages are directed to syslog:
+
+ static void
+ message_callback (
+ guestfs_h *g,
+ void *opaque,
+ uint64_t event,
+ int event_handle,
+ int flags,
+ const char *buf, size_t buf_len,
+ const uint64_t *array, size_t array_len)
+ {
+ const int priority = LOG_USER|LOG_INFO;
+ if (buf_len > 0)
+ syslog (priority, "event 0x%lx: %s", event, buf);
+ }
+
+=head1 PRIVATE DATA AREA
+
+You can attach named pieces of private data to the libguestfs handle,
+fetch them by name, and walk over them, for the lifetime of the
+handle. This is called the private data area and is only available
+from the C API.
+
+To attach a named piece of data, use the following call:
+
+ void guestfs_set_private (guestfs_h *g, const char *key, void *data);
+
+C<key> is the name to associate with this data, and C<data> is an
+arbitrary pointer (which can be C<NULL>). Any previous item with the
+same key is overwritten.
+
+You can use any C<key> you want, but your key should I<not> start with
+an underscore character. Keys beginning with an underscore character
+are reserved for internal libguestfs purposes (eg. for implementing
+language bindings). It is recommended that you prefix the key with
+some unique string to avoid collisions with other users.
+
+To retrieve the pointer, use:
+
+ void *guestfs_get_private (guestfs_h *g, const char *key);
+
+This function returns C<NULL> if either no data is found associated
+with C<key>, or if the user previously set the C<key>'s C<data>
+pointer to C<NULL>.
+
+Libguestfs does not try to look at or interpret the C<data> pointer in
+any way. As far as libguestfs is concerned, it need not be a valid
+pointer at all. In particular, libguestfs does I<not> try to free the
+data when the handle is closed. If the data must be freed, then the
+caller must either free it before calling L</guestfs_close> or must
+set up a close callback to do it (see L</GUESTFS_EVENT_CLOSE>).
+
+To walk over all entries, use these two functions:
+
+ void *guestfs_first_private (guestfs_h *g, const char **key_rtn);
+
+ void *guestfs_next_private (guestfs_h *g, const char **key_rtn);
+
+C<guestfs_first_private> returns the first key, pointer pair ("first"
+does not have any particular meaning -- keys are not returned in any
+defined order). A pointer to the key is returned in C<*key_rtn> and
+the corresponding data pointer is returned from the function. C<NULL>
+is returned if there are no keys stored in the handle.
+
+C<guestfs_next_private> returns the next key, pointer pair. The
+return value of this function is also C<NULL> is there are no further
+entries to return.
+
+Notes about walking over entries:
=over 4
=item *
-Is the string a parameter which is a device or partition name?
+You must not call C<guestfs_set_private> while walking over the
+entries.
=item *
-Does the string begin with C</dev/sd>?
+The handle maintains an internal iterator which is reset when you call
+C<guestfs_first_private>. This internal iterator is invalidated when
+you call C<guestfs_set_private>.
=item *
-Does the named device exist? If so, we use that device.
-However if I<not> then we continue with this algorithm.
+If you have set the data pointer associated with a key to C<NULL>, ie:
+
+ guestfs_set_private (g, key, NULL);
+
+then that C<key> is not returned when walking.
=item *
-Replace initial C</dev/sd> string with C</dev/hd>.
+C<*key_rtn> is only valid until the next call to
+C<guestfs_first_private>, C<guestfs_next_private> or
+C<guestfs_set_private>.
-For example, change C</dev/sda2> to C</dev/hda2>.
+=back
-If that named device exists, use it. If not, continue.
+The following example code shows how to print all keys and data
+pointers that are associated with the handle C<g>:
-=item *
+ const char *key;
+ void *data = guestfs_first_private (g, &key);
+ while (data != NULL)
+ {
+ printf ("key = %s, data = %p\n", key, data);
+ data = guestfs_next_private (g, &key);
+ }
-Replace initial C</dev/sd> string with C</dev/vd>.
+More commonly you are only interested in keys that begin with an
+application-specific prefix C<foo_>. Modify the loop like so:
-If that named device exists, use it. If not, return an error.
+ const char *key;
+ void *data = guestfs_first_private (g, &key);
+ while (data != NULL)
+ {
+ if (strncmp (key, "foo_", strlen ("foo_")) == 0)
+ printf ("key = %s, data = %p\n", key, data);
+ data = guestfs_next_private (g, &key);
+ }
-=back
+If you need to modify keys while walking, then you have to jump back
+to the beginning of the loop. For example, to delete all keys
+prefixed with C<foo_>:
+
+ const char *key;
+ void *data;
+ again:
+ data = guestfs_first_private (g, &key);
+ while (data != NULL)
+ {
+ if (strncmp (key, "foo_", strlen ("foo_")) == 0)
+ {
+ guestfs_set_private (g, key, NULL);
+ /* note that 'key' pointer is now invalid, and so is
+ the internal iterator */
+ goto again;
+ }
+ data = guestfs_next_private (g, &key);
+ }
+
+Note that the above loop is guaranteed to terminate because the keys
+are being deleted, but other manipulations of keys within the loop
+might not terminate unless you also maintain an indication of which
+keys have been visited.
-=head2 PORTABILITY CONCERNS
+=begin html
-Although the standard naming scheme and automatic translation is
-useful for simple programs and guestfish scripts, for larger programs
-it is best not to rely on this mechanism.
+<!-- old anchor for the next section -->
+<a name="state_machine_and_low_level_event_api"/>
-Where possible for maximum future portability programs using
-libguestfs should use these future-proof techniques:
+=end html
-=over 4
+=head1 ARCHITECTURE
+
+Internally, libguestfs is implemented by running an appliance (a
+special type of small virtual machine) using L<qemu(1)>. Qemu runs as
+a child process of the main program.
+
+ ___________________
+ / \
+ | main program |
+ | |
+ | | child process / appliance
+ | | __________________________
+ | | / qemu \
+ +-------------------+ RPC | +-----------------+ |
+ | libguestfs <--------------------> guestfsd | |
+ | | | +-----------------+ |
+ \___________________/ | | Linux kernel | |
+ | +--^--------------+ |
+ \_________|________________/
+ |
+ _______v______
+ / \
+ | Device or |
+ | disk image |
+ \______________/
+
+The library, linked to the main program, creates the child process and
+hence the appliance in the L</guestfs_launch> function.
+
+Inside the appliance is a Linux kernel and a complete stack of
+userspace tools (such as LVM and ext2 programs) and a small
+controlling daemon called L</guestfsd>. The library talks to
+L</guestfsd> using remote procedure calls (RPC). There is a mostly
+one-to-one correspondence between libguestfs API calls and RPC calls
+to the daemon. Lastly the disk image(s) are attached to the qemu
+process which translates device access by the appliance's Linux kernel
+into accesses to the image.
+
+A common misunderstanding is that the appliance "is" the virtual
+machine. Although the disk image you are attached to might also be
+used by some virtual machine, libguestfs doesn't know or care about
+this. (But you will care if both libguestfs's qemu process and your
+virtual machine are trying to update the disk image at the same time,
+since these usually results in massive disk corruption).
+
+=head1 STATE MACHINE
+
+libguestfs uses a state machine to model the child process:
+
+ |
+ guestfs_create
+ |
+ |
+ ____V_____
+ / \
+ | CONFIG |
+ \__________/
+ ^ ^ ^ \
+ / | \ \ guestfs_launch
+ / | _\__V______
+ / | / \
+ / | | LAUNCHING |
+ / | \___________/
+ / | /
+ / | guestfs_launch
+ / | /
+ ______ / __|____V
+ / \ ------> / \
+ | BUSY | | READY |
+ \______/ <------ \________/
-=item *
+The normal transitions are (1) CONFIG (when the handle is created, but
+there is no child process), (2) LAUNCHING (when the child process is
+booting up), (3) alternating between READY and BUSY as commands are
+issued to, and carried out by, the child process.
-Use L</guestfs_list_devices> or L</guestfs_list_partitions> to list
-actual device names, and then use those names directly.
+The guest may be killed by L</guestfs_kill_subprocess>, or may die
+asynchronously at any time (eg. due to some internal error), and that
+causes the state to transition back to CONFIG.
-Since those device names exist by definition, they will never be
-translated.
+Configuration commands for qemu such as L</guestfs_add_drive> can only
+be issued when in the CONFIG state.
-=item *
+The API offers one call that goes from CONFIG through LAUNCHING to
+READY. L</guestfs_launch> blocks until the child process is READY to
+accept commands (or until some failure or timeout).
+L</guestfs_launch> internally moves the state from CONFIG to LAUNCHING
+while it is running.
-Use higher level ways to identify filesystems, such as LVM names,
-UUIDs and filesystem labels.
+API actions such as L</guestfs_mount> can only be issued when in the
+READY state. These API calls block waiting for the command to be
+carried out (ie. the state to transition to BUSY and then back to
+READY). There are no non-blocking versions, and no way to issue more
+than one command per handle at the same time.
-=back
+Finally, the child process sends asynchronous messages back to the
+main program, such as kernel log messages. You can register a
+callback to receive these messages.
=head1 INTERNALS
how the receiver knows what type of args structure to expect, or none
at all.
+For functions that take optional arguments, the optional arguments are
+encoded in the C<guestfs_I<foo>_args> structure in the same way as
+ordinary arguments. A bitmask in the header indicates which optional
+arguments are meaningful. The bitmask is also checked to see if it
+contains bits set which the daemon does not know about (eg. if more
+optional arguments were added in a later version of the library), and
+this causes the call to be rejected.
+
The reply message for ordinary functions is:
total length (header + ret,
=head3 INITIAL MESSAGE
-Because the underlying channel (QEmu -net channel) doesn't have any
-sort of connection control, when the daemon launches it sends an
-initial word (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest
-and daemon is alive. This is what L</guestfs_launch> waits for.
-
-=head1 MULTIPLE HANDLES AND MULTIPLE THREADS
-
-All high-level libguestfs actions are synchronous. If you want
-to use libguestfs asynchronously then you must create a thread.
-
-Only use the handle from a single thread. Either use the handle
-exclusively from one thread, or provide your own mutex so that two
-threads cannot issue calls on the same handle at the same time.
-
-=head1 QEMU WRAPPERS
-
-If you want to compile your own qemu, run qemu from a non-standard
-location, or pass extra arguments to qemu, then you can write a
-shell-script wrapper around qemu.
-
-There is one important rule to remember: you I<must C<exec qemu>> as
-the last command in the shell script (so that qemu replaces the shell
-and becomes the direct child of the libguestfs-using program). If you
-don't do this, then the qemu process won't be cleaned up correctly.
+When the daemon launches it sends an initial word
+(C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest and daemon is
+alive. This is what L</guestfs_launch> waits for.
-Here is an example of a wrapper, where I have built my own copy of
-qemu from source:
-
- #!/bin/sh -
- qemudir=/home/rjones/d/qemu
- exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
+=head3 PROGRESS NOTIFICATION MESSAGES
-Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
-and then use it by setting the LIBGUESTFS_QEMU environment variable.
-For example:
+The daemon may send progress notification messages at any time. These
+are distinguished by the normal length word being replaced by
+C<GUESTFS_PROGRESS_FLAG>, followed by a fixed size progress message.
- LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
+The library turns them into progress callbacks (see
+L</GUESTFS_EVENT_PROGRESS>) if there is a callback registered, or
+discards them if not.
-Note that libguestfs also calls qemu with the -help and -version
-options in order to determine features.
+The daemon self-limits the frequency of progress messages it sends
+(see C<daemon/proto.c:notify_progress>). Not all calls generate
+progress messages.
=head1 LIBGUESTFS VERSION NUMBERS
backporting fixes from development, that branch will stabilize over
time.
+=head1 EXTENDING LIBGUESTFS
+
+=head2 ADDING A NEW API ACTION
+
+Large amounts of boilerplate code in libguestfs (RPC, bindings,
+documentation) are generated, and this makes it easy to extend the
+libguestfs API.
+
+To add a new API action there are two changes:
+
+=over 4
+
+=item 1.
+
+You need to add a description of the call (name, parameters, return
+type, tests, documentation) to C<generator/generator_actions.ml>.
+
+There are two sorts of API action, depending on whether the call goes
+through to the daemon in the appliance, or is serviced entirely by the
+library (see L</ARCHITECTURE> above). L</guestfs_sync> is an example
+of the former, since the sync is done in the appliance.
+L</guestfs_set_trace> is an example of the latter, since a trace flag
+is maintained in the handle and all tracing is done on the library
+side.
+
+Most new actions are of the first type, and get added to the
+C<daemon_functions> list. Each function has a unique procedure number
+used in the RPC protocol which is assigned to that action when we
+publish libguestfs and cannot be reused. Take the latest procedure
+number and increment it.
+
+For library-only actions of the second type, add to the
+C<non_daemon_functions> list. Since these functions are serviced by
+the library and do not travel over the RPC mechanism to the daemon,
+these functions do not need a procedure number, and so the procedure
+number is set to C<-1>.
+
+=item 2.
+
+Implement the action (in C):
+
+For daemon actions, implement the function C<do_E<lt>nameE<gt>> in the
+C<daemon/> directory.
+
+For library actions, implement the function C<guestfs__E<lt>nameE<gt>>
+(note: double underscore) in the C<src/> directory.
+
+In either case, use another function as an example of what to do.
+
+=back
+
+After making these changes, use C<make> to compile.
+
+Note that you don't need to implement the RPC, language bindings,
+manual pages or anything else. It's all automatically generated from
+the OCaml description.
+
+=head2 ADDING TESTS FOR AN API ACTION
+
+You can supply zero or as many tests as you want per API call. The
+tests can either be added as part of the API description
+(C<generator/generator_actions.ml>), or in some rarer cases you may
+want to drop a script into C<regressions/>. Note that adding a script
+to C<regressions/> is slower, so if possible use the first method.
+
+The following describes the test environment used when you add an API
+test in C<generator_actions.ml>.
+
+The test environment has 4 block devices:
+
+=over 4
+
+=item C</dev/sda> 500MB
+
+General block device for testing.
+
+=item C</dev/sdb> 50MB
+
+C</dev/sdb1> is an ext2 filesystem used for testing
+filesystem write operations.
+
+=item C</dev/sdc> 10MB
+
+Used in a few tests where two block devices are needed.
+
+=item C</dev/sdd>
+
+ISO with fixed content (see C<images/test.iso>).
+
+=back
+
+To be able to run the tests in a reasonable amount of time, the
+libguestfs appliance and block devices are reused between tests. So
+don't try testing L</guestfs_kill_subprocess> :-x
+
+Each test starts with an initial scenario, selected using one of the
+C<Init*> expressions, described in C<generator/generator_types.ml>.
+These initialize the disks mentioned above in a particular way as
+documented in C<generator_types.ml>. You should not assume anything
+about the previous contents of other disks that are not initialized.
+
+You can add a prerequisite clause to any individual test. This is a
+run-time check, which, if it fails, causes the test to be skipped.
+Useful if testing a command which might not work on all variations of
+libguestfs builds. A test that has prerequisite of C<Always> means to
+run unconditionally.
+
+In addition, packagers can skip individual tests by setting
+environment variables before running C<make check>.
+
+ SKIP_TEST_<CMD>_<NUM>=1
+
+eg: C<SKIP_TEST_COMMAND_3=1> skips test #3 of L</guestfs_command>.
+
+or:
+
+ SKIP_TEST_<CMD>=1
+
+eg: C<SKIP_TEST_ZEROFREE=1> skips all L</guestfs_zerofree> tests.
+
+Packagers can run only certain tests by setting for example:
+
+ TEST_ONLY="vfs_type zerofree"
+
+See C<capitests/tests.c> for more details of how these environment
+variables work.
+
+=head2 DEBUGGING NEW API ACTIONS
+
+Test new actions work before submitting them.
+
+You can use guestfish to try out new commands.
+
+Debugging the daemon is a problem because it runs inside a minimal
+environment. However you can fprintf messages in the daemon to
+stderr, and they will show up if you use C<guestfish -v>.
+
+=head2 FORMATTING CODE AND OTHER CONVENTIONS
+
+Our C source code generally adheres to some basic code-formatting
+conventions. The existing code base is not totally consistent on this
+front, but we do prefer that contributed code be formatted similarly.
+In short, use spaces-not-TABs for indentation, use 2 spaces for each
+indentation level, and other than that, follow the K&R style.
+
+If you use Emacs, add the following to one of one of your start-up files
+(e.g., ~/.emacs), to help ensure that you get indentation right:
+
+ ;;; In libguestfs, indent with spaces everywhere (not TABs).
+ ;;; Exceptions: Makefile and ChangeLog modes.
+ (add-hook 'find-file-hook
+ '(lambda () (if (and buffer-file-name
+ (string-match "/libguestfs\\>"
+ (buffer-file-name))
+ (not (string-equal mode-name "Change Log"))
+ (not (string-equal mode-name "Makefile")))
+ (setq indent-tabs-mode nil))))
+
+ ;;; When editing C sources in libguestfs, use this style.
+ (defun libguestfs-c-mode ()
+ "C mode with adjusted defaults for use with libguestfs."
+ (interactive)
+ (c-set-style "K&R")
+ (setq c-indent-level 2)
+ (setq c-basic-offset 2))
+ (add-hook 'c-mode-hook
+ '(lambda () (if (string-match "/libguestfs\\>"
+ (buffer-file-name))
+ (libguestfs-c-mode))))
+
+Enable warnings when compiling (and fix any problems this
+finds):
+
+ ./configure --enable-gcc-warnings
+
+Useful targets are:
+
+ make syntax-check # checks the syntax of the C code
+ make check # runs the test suite
+
+=head2 DAEMON CUSTOM PRINTF FORMATTERS
+
+In the daemon code we have created custom printf formatters C<%Q> and
+C<%R>, which are used to do shell quoting.
+
+=over 4
+
+=item %Q
+
+Simple shell quoted string. Any spaces or other shell characters are
+escaped for you.
+
+=item %R
+
+Same as C<%Q> except the string is treated as a path which is prefixed
+by the sysroot.
+
+=back
+
+For example:
+
+ asprintf (&cmd, "cat %R", path);
+
+would produce C<cat /sysroot/some\ path\ with\ spaces>
+
+I<Note:> Do I<not> use these when you are passing parameters to the
+C<command{,r,v,rv}()> functions. These parameters do NOT need to be
+quoted because they are not passed via the shell (instead, straight to
+exec). You probably want to use the C<sysroot_path()> function
+however.
+
+=head2 SUBMITTING YOUR NEW API ACTIONS
+
+Submit patches to the mailing list:
+L<http://www.redhat.com/mailman/listinfo/libguestfs>
+and CC to L<rjones@redhat.com>.
+
+=head2 INTERNATIONALIZATION (I18N) SUPPORT
+
+We support i18n (gettext anyhow) in the library.
+
+However many messages come from the daemon, and we don't translate
+those at the moment. One reason is that the appliance generally has
+all locale files removed from it, because they take up a lot of space.
+So we'd have to readd some of those, as well as copying our PO files
+into the appliance.
+
+Debugging messages are never translated, since they are intended for
+the programmers.
+
+=head2 SOURCE CODE SUBDIRECTORIES
+
+=over 4
+
+=item C<appliance>
+
+The libguestfs appliance, build scripts and so on.
+
+=item C<capitests>
+
+Automated tests of the C API.
+
+=item C<cat>
+
+The L<virt-cat(1)>, L<virt-filesystems(1)> and L<virt-ls(1)> commands
+and documentation.
+
+=item C<contrib>
+
+Outside contributions, experimental parts.
+
+=item C<daemon>
+
+The daemon that runs inside the libguestfs appliance and carries out
+actions.
+
+=item C<df>
+
+L<virt-df(1)> command and documentation.
+
+=item C<edit>
+
+L<virt-edit(1)> command and documentation.
+
+=item C<examples>
+
+C API example code.
+
+=item C<fish>
+
+L<guestfish(1)>, the command-line shell, and various shell scripts
+built on top such as L<virt-copy-in(1)>, L<virt-copy-out(1)>,
+L<virt-tar-in(1)>, L<virt-tar-out(1)>.
+
+=item C<fuse>
+
+L<guestmount(1)>, FUSE (userspace filesystem) built on top of libguestfs.
+
+=item C<generator>
+
+The crucially important generator, used to automatically generate
+large amounts of boilerplate C code for things like RPC and bindings.
+
+=item C<images>
+
+Files used by the test suite.
+
+Some "phony" guest images which we test against.
+
+=item C<inspector>
+
+L<virt-inspector(1)>, the virtual machine image inspector.
+
+=item C<logo>
+
+Logo used on the website. The fish is called Arthur by the way.
+
+=item C<m4>
+
+M4 macros used by autoconf.
+
+=item C<po>
+
+Translations of simple gettext strings.
+
+=item C<po-docs>
+
+The build infrastructure and PO files for translations of manpages and
+POD files. Eventually this will be combined with the C<po> directory,
+but that is rather complicated.
+
+=item C<regressions>
+
+Regression tests.
+
+=item C<rescue>
+
+L<virt-rescue(1)> command and documentation.
+
+=item C<src>
+
+Source code to the C library.
+
+=item C<tools>
+
+Command line tools written in Perl (L<virt-resize(1)> and many others).
+
+=item C<test-tool>
+
+Test tool for end users to test if their qemu/kernel combination
+will work with libguestfs.
+
+=item C<csharp>
+
+=item C<haskell>
+
+=item C<java>
+
+=item C<ocaml>
+
+=item C<php>
+
+=item C<perl>
+
+=item C<python>
+
+=item C<ruby>
+
+Language bindings.
+
+=back
+
+=head1 LIMITS
+
+=head2 PROTOCOL LIMITS
+
+Internally libguestfs uses a message-based protocol to pass API calls
+and their responses to and from a small "appliance" (see L</INTERNALS>
+for plenty more detail about this). The maximum message size used by
+the protocol is slightly less than 4 MB. For some API calls you may
+need to be aware of this limit. The API calls which may be affected
+are individually documented, with a link back to this section of the
+documentation.
+
+A simple call such as L</guestfs_cat> returns its result (the file
+data) in a simple string. Because this string is at some point
+internally encoded as a message, the maximum size that it can return
+is slightly under 4 MB. If the requested file is larger than this
+then you will get an error.
+
+In order to transfer large files into and out of the guest filesystem,
+you need to use particular calls that support this. The sections
+L</UPLOADING> and L</DOWNLOADING> document how to do this.
+
+You might also consider mounting the disk image using our FUSE
+filesystem support (L<guestmount(1)>).
+
+=head2 MAXIMUM NUMBER OF DISKS
+
+When using virtio disks (the default) the current limit is B<25>
+disks.
+
+Virtio itself consumes 1 virtual PCI slot per disk, and PCI is limited
+to 31 slots. However febootstrap only understands disks with names
+C</dev/vda> through C</dev/vdz> (26 letters) and it reserves one disk
+for its own purposes.
+
+We are working to substantially raise this limit in future versions
+but it requires complex changes to qemu.
+
+In future versions of libguestfs it should also be possible to "hot
+plug" disks (add and remove disks after calling L</guestfs_launch>).
+This also requires changes to qemu.
+
+=head2 MAXIMUM NUMBER OF PARTITIONS PER DISK
+
+Virtio limits the maximum number of partitions per disk to B<15>.
+
+This is because it reserves 4 bits for the minor device number (thus
+C</dev/vda>, and C</dev/vda1> through C</dev/vda15>).
+
+If you attach a disk with more than 15 partitions, the extra
+partitions are ignored by libguestfs.
+
+=head2 MAXIMUM SIZE OF A DISK
+
+Probably the limit is between 2**63-1 and 2**64-1 bytes.
+
+We have tested block devices up to 1 exabyte (2**60 or
+1,152,921,504,606,846,976 bytes) using sparse files backed by an XFS
+host filesystem.
+
+Although libguestfs probably does not impose any limit, the underlying
+host storage will. If you store disk images on a host ext4
+filesystem, then the maximum size will be limited by the maximum ext4
+file size (currently 16 TB). If you store disk images as host logical
+volumes then you are limited by the maximum size of an LV.
+
+For the hugest disk image files, we recommend using XFS on the host
+for storage.
+
+=head2 MAXIMUM SIZE OF A PARTITION
+
+The MBR (ie. classic MS-DOS) partitioning scheme uses 32 bit sector
+numbers. Assuming a 512 byte sector size, this means that MBR cannot
+address a partition located beyond 2 TB on the disk.
+
+It is recommended that you use GPT partitions on disks which are
+larger than this size. GPT uses 64 bit sector numbers and so can
+address partitions which are theoretically larger than the largest
+disk we could support.
+
+=head2 MAXIMUM SIZE OF A FILESYSTEM, FILES, DIRECTORIES
+
+This depends on the filesystem type. libguestfs itself does not
+impose any known limit. Consult Wikipedia or the filesystem
+documentation to find out what these limits are.
+
+=head2 MAXIMUM UPLOAD AND DOWNLOAD
+
+The API functions L</guestfs_upload>, L</guestfs_download>,
+L</guestfs_tar_in>, L</guestfs_tar_out> and the like allow unlimited
+sized uploads and downloads.
+
+=head2 INSPECTION LIMITS
+
+The inspection code has several arbitrary limits on things like the
+size of Windows Registry hive it will read, and the length of product
+name. These are intended to stop a malicious guest from consuming
+arbitrary amounts of memory and disk space on the host, and should not
+be reached in practice. See the source code for more information.
+
=head1 ENVIRONMENT VARIABLES
=over 4
=item LIBGUESTFS_PATH
-Set the path that libguestfs uses to search for kernel and initrd.img.
-See the discussion of paths in section PATH above.
+Set the path that libguestfs uses to search for a supermin appliance.
+See the discussion of paths in section L</PATH> above.
=item LIBGUESTFS_QEMU
=item TMPDIR
-Location of temporary directory, defaults to C</tmp>.
+Location of temporary directory, defaults to C</tmp> except for the
+cached supermin appliance which defaults to C</var/tmp>.
-If libguestfs was compiled to use the supermin appliance then each
-handle will require rather a large amount of space in this directory
-for short periods of time (~ 80 MB). You can use C<$TMPDIR> to
-configure another directory to use in case C</tmp> is not large
+If libguestfs was compiled to use the supermin appliance then the
+real appliance is cached in this directory, shared between all
+handles belonging to the same EUID. You can use C<$TMPDIR> to
+configure another directory to use in case C</var/tmp> is not large
enough.
=back
=head1 SEE ALSO
+L<guestfs-examples(3)>,
+L<guestfs-ocaml(3)>,
+L<guestfs-python(3)>,
+L<guestfs-ruby(3)>,
L<guestfish(1)>,
L<guestmount(1)>,
L<virt-cat(1)>,
+L<virt-copy-in(1)>,
+L<virt-copy-out(1)>,
L<virt-df(1)>,
L<virt-edit(1)>,
+L<virt-filesystems(1)>,
L<virt-inspector(1)>,
L<virt-list-filesystems(1)>,
L<virt-list-partitions(1)>,
L<virt-make-fs(1)>,
L<virt-rescue(1)>,
L<virt-tar(1)>,
+L<virt-tar-in(1)>,
+L<virt-tar-out(1)>,
L<virt-win-reg(1)>,
L<qemu(1)>,
L<febootstrap(1)>,
=head1 COPYRIGHT
-Copyright (C) 2009-2010 Red Hat Inc.
+Copyright (C) 2009-2011 Red Hat Inc.
L<http://libguestfs.org/>
This library is free software; you can redistribute it and/or
git.annexia.org / libguestfs.git / blobdiff