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
This section provides a gentler overview of the libguestfs API. We
also try to group API calls together, where that may not be obvious
-from reading about the individual calls below.
+from reading about the individual calls in the main section of this
+manual.
=head2 HANDLES
/* 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).
+ * then you *must* sync). See also: guestfs_umount and
+ * guestfs_umount_all calls.
*/
guestfs_sync (g);
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 C<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
C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
one you added), etc.
-Once C<guestfs_launch> has been called you cannot add any more images.
-You can call C<guestfs_list_devices> to get a list of the device
+Once L</guestfs_launch> has been called you cannot add any more images.
+You can call L</guestfs_list_devices> to get a list of the device
names, in the order that you added them. See also L</BLOCK DEVICE
NAMING> below.
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 C<guestfs_mount>. If you already know that a disk
+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:
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
-C<guestfs_list_partitions> and C<guestfs_lvs> to list possible
+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 C<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)>.
+mountable, or else examine them with L</guestfs_vfs_type> or
+L</guestfs_file>. Libguestfs also has a set of APIs for inspection of
+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 C<guestfs_mount_ro>. There are
+To mount a disk image read-only, use L</guestfs_mount_ro>. There are
several other variations of the C<guestfs_mount_*> call.
=head2 FILESYSTEM ACCESS AND MODIFICATION
can find listed in detail below in this man page, and we don't even
pretend to cover them all in this overview.
-Specify filenames as full paths including the mount point.
+Specify filenames as full paths, starting with C<"/"> and including
+the mount point.
For example, if you mounted a filesystem at C<"/"> and you want to
read the file called C<"etc/passwd"> then you could do:
guestfs_ln_s (g, "/etc/init.d/portmap",
"/etc/rc3.d/S30portmap");
-Libguestfs will reject attempts to use relative paths. There is no
-concept of a current working directory. Libguestfs can return errors
-in many situations: for example if the filesystem isn't writable, or
-if a file or directory that you requested doesn't exist. If you are
-using the C API (documented here) you have to check for those error
-conditions after each call. (Other language bindings turn these
-errors into exceptions).
+Libguestfs will reject attempts to use relative paths and there is no
+concept of a current working directory.
+
+Libguestfs can return errors in many situations: for example if the
+filesystem isn't writable, or if a file or directory that you
+requested doesn't exist. If you are using the C API (documented here)
+you have to check for those error conditions after each call. (Other
+language bindings turn these errors into exceptions).
File writes are affected by the per-handle umask, set by calling
-C<guestfs_umask> and defaulting to 022.
+L</guestfs_umask> and defaulting to 022. See L</UMASK>.
=head2 PARTITIONING
tables on disk images.
In the common case where you want to create a single partition
-covering the whole disk, you should use the C<guestfs_part_disk>
+covering the whole disk, you should use the L</guestfs_part_disk>
call:
const char *parttype = "mbr";
Obviously this effectively wipes anything that was on that disk image
before.
-In general MBR partitions are both unnecessarily complicated and
-depend on archaic details, namely the Cylinder-Head-Sector (CHS)
-geometry of the disk. C<guestfs_sfdiskM> can be used to
-create more complex arrangements where the relative sizes are
-expressed in megabytes instead of cylinders, which is a small win.
-C<guestfs_sfdiskM> will choose the nearest cylinder to approximate the
-requested size. There's a lot of crazy stuff to do with IDE and
-virtio disks having different, incompatible CHS geometries, that you
-probably don't want to know about.
-
-My advice: make a single partition to cover the whole disk, then use
-LVM on top.
-
=head2 LVM2
Libguestfs provides access to a large part of the LVM2 API, such as
-C<guestfs_lvcreate> and C<guestfs_vgremove>. It won't make much sense
+L</guestfs_lvcreate> and L</guestfs_vgremove>. It won't make much sense
unless you familiarize yourself with the concepts of physical volumes,
volume groups and logical volumes.
=head2 DOWNLOADING
-Use C<guestfs_cat> to download small, text only files. This call
+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.
-C<guestfs_read_file> can be used to read files which contain
+L</guestfs_read_file> can be used to read files which contain
arbitrary 8 bit data, since it returns a (pointer, size) pair.
However it is still limited to "small" files, less than 2 MB.
-C<guestfs_download> can be used to download any file, with no
+L</guestfs_download> can be used to download any file, with no
limits on content or size (even files larger than 4 GB).
-To download multiple files, see C<guestfs_tar_out> and
-C<guestfs_tgz_out>.
+To download multiple files, see L</guestfs_tar_out> and
+L</guestfs_tgz_out>.
=head2 UPLOADING
It's often the case that you want to write a file or files to the disk
image.
-For small, single files, use C<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 C<guestfs_upload>. This call has no
+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).
-To upload multiple files, see C<guestfs_tar_in> and C<guestfs_tgz_in>.
+To upload multiple files, see L</guestfs_tar_in> and L</guestfs_tgz_in>.
However the fastest way to upload I<large numbers of arbitrary files>
is to turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
-L<mkisofs(8)>), then attach this using C<guestfs_add_drive_ro>. If
+L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>. If
you add the drive in a predictable way (eg. adding it last after all
other drives) then you can get the device name from
-C<guestfs_list_devices> and mount it directly using
-C<guestfs_mount_ro>. Note that squashfs images are sometimes
+L</guestfs_list_devices> and mount it directly using
+L</guestfs_mount_ro>. Note that squashfs images are sometimes
non-portable between kernel versions, and they don't support labels or
UUIDs. If you want to pre-build an image or you need to mount it
using a label or UUID, use an ISO image instead.
guestfs_dd (g, "/dev/VG/Original", "/dev/VG/Copy");
The destination (C</dev/VG/Copy>) must be at least as large as the
-source (C</dev/VG/Original>).
+source (C</dev/VG/Original>). To copy less than the whole
+source device, use L</guestfs_copy_size>.
=item B<file on the host> to B<file or device>
=head2 LISTING FILES
-C<guestfs_ll> is just designed for humans to read (mainly when using
+L</guestfs_ll> is just designed for humans to read (mainly when using
the L<guestfish(1)>-equivalent command C<ll>).
-C<guestfs_ls> is a quick way to get a list of files in a directory
+L</guestfs_ls> is a quick way to get a list of files in a directory
from programs, as a flat list of strings.
-C<guestfs_readdir> is a programmatic way to get a list of files in a
+L</guestfs_readdir> is a programmatic way to get a list of files in a
directory, plus additional information about each one. It is more
equivalent to using the L<readdir(3)> call on a local filesystem.
-C<guestfs_find> can be used to recursively list files.
+L</guestfs_find> and L</guestfs_find0> can be used to recursively list
+files.
=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 C<guestfs_command> and
-C<guestfs_sh> (there are also variations).
+The two main API calls to run commands are L</guestfs_command> and
+L</guestfs_sh> (there are also variations).
-The difference is that C<guestfs_sh> runs commands using the shell, so
+The difference is that L</guestfs_sh> runs commands using the shell, so
any shell globs, redirections, etc will work.
=head2 CONFIGURATION FILES
documentation on the L<http://augeas.net/> website.
If you don't want to use Augeas (you fool!) then try calling
-C<guestfs_read_lines> to get the file as a list of lines which
+L</guestfs_read_lines> to get the file as a list of lines which
you can iterate over.
=head2 SELINUX
for example by running the external command
C<restorecon pathname>.
+=head2 UMASK
+
+Certain calls are affected by the current file mode creation mask (the
+"umask"). In particular ones which create files or directories, such
+as L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>. This
+affects either the default mode that the file is created with or
+modifies the mode that you supply.
+
+The default umask is C<022>, so files are created with modes such as
+C<0644> and directories with C<0755>.
+
+There are two ways to avoid being affected by umask. Either set umask
+to 0 (call C<guestfs_umask (g, 0)> early after launching). Or call
+L</guestfs_chmod> after creating each file or directory.
+
+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. (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.
+
=head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
Libguestfs can mount NTFS partitions. It does this using the
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)>).
+also L<hivex(3)> and L<virt-inspector(1)>).
Replacing backslash characters with forward slash characters is also
outside the scope of libguestfs, but something that you can easily do.
Where we can help is in resolving the case insensitivity of paths.
-For this, call C<guestfs_case_sensitive_path>.
+For this, call L</guestfs_case_sensitive_path>.
Libguestfs also provides some help for decoding Windows Registry
"hive" files, through the library C<hivex> which is part of the
-libguestfs project. You have to locate and download the hive file(s)
-yourself, and then pass them to C<hivex> functions. See also the
-programs L<hivexml(1)>, L<hivexsh(1)> and L<virt-win-reg(1)> for more
-help on this issue.
+libguestfs project although ships as a separate tarball. You have to
+locate and download the hive file(s) yourself, and then pass them to
+C<hivex> functions. See also the programs L<hivexml(1)>,
+L<hivexsh(1)>, L<hivexregedit(1)> and L<virt-win-reg(1)> for more help
+on this issue.
=head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
=item B<C++>
You can use the I<guestfs.h> header file from C++ programs. The C++
-API is identical to the C API. C++ classes and exceptions are
-not implemented.
+API is identical to the C API. C++ classes and exceptions are not
+used.
=item B<C#>
=item B<Haskell>
-This is the only language binding that working but incomplete. Only
-calls which return simple integers have been bound in Haskell, and we
-are looking for help to complete this binding.
+This is the only language binding that is working but incomplete.
+Only calls which return simple integers have been bound in Haskell,
+and we are looking for help to complete this binding.
=item B<Java>
For documentation see L<Sys::Guestfs(3)>.
+=item B<PHP>
+
+For documentation see C<README-PHP> supplied with libguestfs
+sources or in the php-libguestfs package for your distribution.
+
+The PHP binding only works correctly on 64 bit machines.
+
=item B<Python>
For documentation do:
changes won't be written out, or will be partially written, or (very
rarely) that you'll get disk corruption.
-Note that in L<guestfish(3)> I<autosync is the default>. So quick and
+Note that in L<guestfish(3)> autosync is the default. So quick and
dirty guestfish scripts that forget to sync will work just fine, which
-can make this extra-puzzling if you are trying to debug a problem.
+can make this very puzzling if you are trying to debug a problem.
+
+Update: Autosync is enabled by default for all API users starting from
+libguestfs 1.5.24.
=item Mount option C<-o sync> should not be the default.
-If you use C<guestfs_mount>, then C<-o sync,noatime> are added
+If you use L</guestfs_mount>, then C<-o sync,noatime> are added
implicitly. However C<-o sync> does not add any reliability benefit,
but does have a very large performance impact.
-The work around is to use C<guestfs_mount_options> and set the mount
+The work around is to use L</guestfs_mount_options> and set the mount
options that you actually want to use.
=item Read-only should be the default.
Note that many filesystems change the disk when you just mount and
unmount, even if you didn't perform any writes. You need to use
-C<guestfs_add_drive_ro> to guarantee that the disk is not changed.
+L</guestfs_add_drive_ro> to guarantee that the disk is not changed.
=item guestfish command line is hard to use.
C<guestfish disk.img> doesn't do what people expect (open C<disk.img>
for examination). It tries to run a guestfish command C<disk.img>
-which doesn't exist, so it fails, and it fails with a strange and
-unintuitive error message. Like the Bourne shell, we should have used
-C<guestfish -c command> to run commands.
+which doesn't exist, so it fails. In earlier versions of guestfish
+the error message was also unintuitive, but we have corrected this
+since. Like the Bourne shell, we should have used C<guestfish -c
+command> to run commands.
+
+=item guestfish megabyte modifiers don't work right on all commands
+
+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).
+
+The most common is L</guestfs_lvcreate>. The guestfish command:
+
+ lvcreate LV VG 100M
+
+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.
+
+This could be fixed in the generator by specially marking parameters
+and return values which take bytes or other units.
+
+=item Ambiguity between devices and paths
+
+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).
+
+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/>.
+
+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:
+
+ type path = Path of string | Device of int | Partition of int * int
+
+which would allow you to pass arguments like:
+
+ 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 *)
+
+As you can see there are still problems to resolve even with this
+representation. Also consider how it might work in guestfish.
=back
are individually documented, with a link back to this section of the
documentation.
-A simple call such as C<guestfs_cat> returns its result (the file
+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
You might also consider mounting the disk image using our FUSE
filesystem support (L<guestmount(1)>).
+=head2 KEYS AND PASSPHRASES
+
+Certain libguestfs calls take a parameter that contains sensitive key
+material, passed in as a C string.
+
+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.
+
+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 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.
+
+See the graphical program guestfs-browser for one possible
+architecture for multithreaded programs using libvirt and libguestfs.
+
+=head2 PATH
+
+Libguestfs needs a kernel and initrd.img, which it finds by looking
+along an internal path.
+
+By default it looks for these in the directory C<$libdir/guestfs>
+(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
+
+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>.
+
+=head2 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.
+
+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 $qemudir/pc-bios "$@"
+
+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:
+
+ LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
+
+Note that libguestfs also calls qemu with the -help and -version
+options in order to determine features.
+
+=head2 ABI GUARANTEE
+
+We guarantee the libguestfs ABI (binary interface), for public,
+high-level actions as outlined in this section. Although we will
+deprecate some actions, for example if they get replaced by newer
+calls, we will keep the old actions forever. This allows you the
+developer to program in confidence against the libguestfs API.
+
+=head2 BLOCK DEVICE NAMING
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+=head3 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
+
+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.
+
+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.
+
+=over 4
+
+=item *
+
+Is the string a parameter which is a device or partition name?
+
+=item *
+
+Does the string begin with C</dev/sd>?
+
+=item *
+
+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).
+
+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 C<guestfs_create>. Call C<guestfs_close>
+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
Create a connection handle.
-You have to call C<guestfs_add_drive> on the handle at least once.
+You have to call L</guestfs_add_drive_opts> (or one of the equivalent
+calls) on the handle at least once.
This function returns a non-NULL pointer to a handle on success or
NULL on error.
-After configuring the handle, you have to call C<guestfs_launch>.
+After configuring the handle, you have to call L</guestfs_launch>.
You may also want to configure error handling for the handle. See
L</ERROR HANDLING> section below.
=head1 ERROR HANDLING
-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 C<guestfs_last_error> and/or by setting up an error
-handler with C<guestfs_set_error_handler>.
+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.
-The default error handler prints the information string to C<stderr>.
+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 C<guestfs_set_out_of_memory_handler>.
+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
returns C<NULL>.
The lifetime of the returned string is until the next error occurs, or
-C<guestfs_close> is called.
+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>.
-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.
+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 *data,
+ void *opaque,
const char *msg);
void guestfs_set_error_handler (guestfs_h *g,
guestfs_error_handler_cb cb,
- void *data);
+ 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.
=head2 guestfs_get_error_handler
guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
- void **data_rtn);
+ void **opaque_rtn);
Returns the current error handler callback.
This returns the current out of memory handler.
-=head1 PATH
-
-Libguestfs needs a kernel and initrd.img, which it finds by looking
-along an internal path.
-
-By default it looks for these in the directory C<$libdir/guestfs>
-(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
-
-Use C<guestfs_set_path> or set the environment variable
-C<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>.
-
-=head1 HIGH-LEVEL API ACTIONS
-
-=head2 ABI GUARANTEE
-
-We guarantee the libguestfs ABI (binary interface), for public,
-high-level actions as outlined in this section. Although we will
-deprecate some actions, for example if they get replaced by newer
-calls, we will keep the old actions forever. This allows you the
-developer to program in confidence against libguestfs.
+=head1 API CALLS
@ACTIONS@
@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
-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:
+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])
at run time, as in this example program (note that you still
need the compile time check as well):
- #include <config.h>
-
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
main ()
{
- #ifdef HAVE_GUESTFS_DD
+ #ifdef LIBGUESTFS_HAVE_DD
void *dl;
int has_function;
Requires: libguestfs >= 1.0.80
-=begin html
+=head1 CALLS WITH OPTIONAL ARGUMENTS
-<!-- old anchor for the next section -->
-<a name="state_machine_and_low_level_event_api"/>
+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:
-=end html
+ int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
-=head1 ARCHITECTURE
+Call this with a list of optional arguments, terminated by C<-1>.
+So to call with no optional arguments specified:
-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.
+ guestfs_add_drive_opts (g, filename, -1);
- ___________________
- / \
- | main program |
- | |
- | | child process / appliance
- | | __________________________
- | | / qemu \
- +-------------------+ RPC | +-----------------+ |
- | libguestfs <--------------------> guestfsd | |
- | | | +-----------------+ |
- \___________________/ | | Linux kernel | |
- | +--^--------------+ |
- \_________|________________/
- |
- _______v______
- / \
- | Device or |
- | disk image |
- \______________/
+With a single optional argument:
-The library, linked to the main program, creates the child process and
-hence the appliance in the L</guestfs_launch> function.
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ -1);
-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 C<guestfsd>. The library talks to
-C<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.
+With two:
-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).
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+ -1);
-=head1 STATE MACHINE
+and so forth. Don't forget the terminating C<-1> otherwise
+Bad Things will happen!
-libguestfs uses a state machine to model the child process:
+=head2 USING va_list FOR OPTIONAL ARGUMENTS
- |
- guestfs_create
- |
- |
- ____V_____
- / \
- | CONFIG |
- \__________/
- ^ ^ ^ \
- / | \ \ guestfs_launch
- / | _\__V______
- / | / \
- / | | LAUNCHING |
- / | \___________/
- / | /
- / | guestfs_launch
- / | /
- ______ / __|____V
- / \ ------> / \
- | BUSY | | READY |
- \______/ <------ \________/
+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:
-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.
+ int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
+ va_list args);
-The guest may be killed by C<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.
+=head2 CONSTRUCTING OPTIONAL ARGUMENTS
-Configuration commands for qemu such as C<guestfs_add_drive> can only
-be issued when in the CONFIG state.
+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:
-The high-level API offers two calls that go from CONFIG through
-LAUNCHING to READY. C<guestfs_launch> blocks until the child process
-is READY to accept commands (or until some failure or timeout).
-C<guestfs_launch> internally moves the state from CONFIG to LAUNCHING
-while it is running.
+ 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);
-High-level API actions such as C<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).
+You could call it like this:
-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.
+ 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.
+
+=back
+
+=head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES
+
+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.
+
+For guestfish, see L<guestfish(1)/OPTIONAL ARGUMENTS>.
=head2 SETTING CALLBACKS TO HANDLE EVENTS
The callback function C<cb> will be called when the child process
quits, either asynchronously or if killed by
-C<guestfs_kill_subprocess>. (This corresponds to a transition from
+L</guestfs_kill_subprocess>. (This corresponds to a transition from
any state to the CONFIG state).
=head2 guestfs_set_launch_done_callback
typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
void guestfs_set_launch_done_callback (guestfs_h *g,
- guestfs_ready_cb cb,
+ guestfs_launch_done_cb cb,
void *opaque);
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).
-=head1 BLOCK DEVICE NAMING
+=head2 guestfs_set_close_callback
-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.
+ typedef void (*guestfs_close_cb) (guestfs_h *g, void *opaque);
+ void guestfs_set_close_callback (guestfs_h *g,
+ guestfs_close_cb cb,
+ void *opaque);
-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 function C<cb> will be called while the handle
+is being closed (synchronously from L</guestfs_close>).
-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.
+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).
-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.
+=head2 guestfs_set_progress_callback
-Note that this I<only> applies to parameters. The
-C<guestfs_list_devices>, C<guestfs_list_partitions> and similar calls
-return the true names of the devices and partitions as known to the
-appliance.
+ typedef void (*guestfs_progress_cb) (guestfs_h *g, void *opaque,
+ int proc_nr, int serial,
+ uint64_t position, uint64_t total);
+ void guestfs_set_progress_callback (guestfs_h *g,
+ guestfs_progress_cb cb,
+ void *opaque);
-=head2 ALGORITHM FOR BLOCK DEVICE NAME TRANSLATION
+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).
-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 C<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.
+The callback receives two numbers: C<position> and C<total>.
+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.
-The algorithm is applied only to I<parameters> which are known to be
-either device or partition names. Return values from functions such
-as C<guestfs_list_devices> are never changed.
+The only defined and stable parts of the API are:
=over 4
=item *
-Is the string a parameter which is a device or partition name?
+The callback can display to the user some type of progress bar or
+indicator which shows the ratio of C<position>:C<total>.
=item *
-Does the string begin with C</dev/sd>?
+0 E<lt>= C<position> E<lt>= C<total>
=item *
-Does the named device exist? If so, we use that device.
-However if I<not> then we continue with this algorithm.
+If any progress notification is sent during a call, then a final
+progress notification is always sent when C<position> = C<total>.
-=item *
+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.
-Replace initial C</dev/sd> string with C</dev/hd>.
+=back
-For example, change C</dev/sda2> to C</dev/hda2>.
+The callback also receives the procedure number and serial number 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.
-If that named device exists, use it. If not, continue.
+=head1 PRIVATE DATA AREA
-=item *
+You can attach named pieces of private data to the libguestfs handle,
+and fetch them by name for the lifetime of the handle. This is called
+the private data area and is only available from the C API.
-Replace initial C</dev/sd> string with C</dev/vd>.
+To attach a named piece of data, use the following call:
-If that named device exists, use it. If not, return an error.
+ void guestfs_set_private (guestfs_h *g, const char *key, void *data);
-=back
+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 name is overwritten.
-=head2 PORTABILITY CONCERNS
+You can use any C<key> you want, but names beginning with an
+underscore character are reserved for internal libguestfs purposes
+(for implementing language bindings). It is recommended to prefix the
+name with some unique string to avoid collisions with other users.
-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.
+To retrieve the pointer, use:
-Where possible for maximum future portability programs using
-libguestfs should use these future-proof techniques:
+ void *guestfs_get_private (guestfs_h *g, const char *key);
-=over 4
+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>.
-=item *
+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_set_close_callback>,
+and note that only one callback can be registered for a handle).
-Use C<guestfs_list_devices> or C<guestfs_list_partitions> to list
-actual device names, and then use those names directly.
+The private data area is implemented using a hash table, and should be
+reasonably efficient for moderate numbers of keys.
-Since those device names exist by definition, they will never be
-translated.
+=begin html
-=item *
+<!-- old anchor for the next section -->
+<a name="state_machine_and_low_level_event_api"/>
-Use higher level ways to identify filesystems, such as LVM names,
-UUIDs and filesystem labels.
+=end html
-=back
+=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 |
+ \______/ <------ \________/
+
+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 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.
+
+Configuration commands for qemu such as L</guestfs_add_drive> can only
+be issued when in the CONFIG state.
+
+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.
+
+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.
+
+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
=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 C<guestfs_launch> waits for.
+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
+=head3 PROGRESS NOTIFICATION MESSAGES
-All high-level libguestfs actions are synchronous. If you want
-to use libguestfs asynchronously then you must create a thread.
+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.
-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 library turns them into progress callbacks (see
+C<guestfs_set_progress_callback>) if there is a callback registered,
+or discards them if not.
-=head1 QEMU WRAPPERS
+The daemon self-limits the frequency of progress messages it sends
+(see C<daemon/proto.c:notify_progress>). Not all calls generate
+progress messages.
-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.
+=head1 LIBGUESTFS VERSION NUMBERS
-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.
+Since April 2010, libguestfs has started to make separate development
+and stable releases, along with corresponding branches in our git
+repository. These separate releases can be identified by version
+number:
-Here is an example of a wrapper, where I have built my own copy of
-qemu from source:
+ even numbers for stable: 1.2.x, 1.4.x, ...
+ .-------- odd numbers for development: 1.3.x, 1.5.x, ...
+ |
+ v
+ 1 . 3 . 5
+ ^ ^
+ | |
+ | `-------- sub-version
+ |
+ `------ always '1' because we don't change the ABI
- #!/bin/sh -
- qemudir=/home/rjones/d/qemu
- exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
+Thus "1.3.5" is the 5th update to the development branch "1.3".
-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:
+As time passes we cherry pick fixes from the development branch and
+backport those into the stable branch, the effect being that the
+stable branch should get more stable and less buggy over time. So the
+stable releases are ideal for people who don't need new features but
+would just like the software to work.
- LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
+Our criteria for backporting changes are:
-Note that libguestfs also calls qemu with the -help and -version
-options in order to determine features.
+=over 4
+
+=item *
+
+Documentation changes which don't affect any code are
+backported unless the documentation refers to a future feature
+which is not in stable.
+
+=item *
+
+Bug fixes which are not controversial, fix obvious problems, and
+have been well tested are backported.
+
+=item *
+
+Simple rearrangements of code which shouldn't affect how it works get
+backported. This is so that the code in the two branches doesn't get
+too far out of step, allowing us to backport future fixes more easily.
+
+=item *
+
+We I<don't> backport new features, new APIs, new tools etc, except in
+one exceptional case: the new feature is required in order to
+implement an important bug fix.
+
+=back
+
+A new stable branch starts when we think the new features in
+development are substantial and compelling enough over the current
+stable branch to warrant it. When that happens we create new stable
+and development versions 1.N.0 and 1.(N+1).0 [N is even]. The new
+dot-oh release won't necessarily be so stable at this point, but by
+backporting fixes from development, that branch will stabilize over
+time.
=head1 ENVIRONMENT VARIABLES
Location of temporary directory, defaults to C</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<$TMPDIR> to
+If libguestfs was compiled to use the supermin appliance then the
+real appliance is cached in this directory, shared between all
+handles belonging to the same EUID. You can use C<$TMPDIR> to
configure another directory to use in case C</tmp> is not large
enough.
=head1 COPYRIGHT
-Copyright (C) 2009 Red Hat Inc.
+Copyright (C) 2009-2010 Red Hat Inc.
L<http://libguestfs.org/>
This library is free software; you can redistribute it and/or
git.annexia.org / libguestfs.git / blobdiff