guestfs_h *handle = guestfs_create ();
guestfs_add_drive (handle, "guest.img");
guestfs_launch (handle);
- guestfs_wait_ready (handle);
guestfs_mount (handle, "/dev/sda1", "/");
guestfs_touch (handle, "/hello");
guestfs_sync (handle);
in the context of the guest. Also you can access filesystems over FTP.
Libguestfs is a library that can be linked with C and C++ management
-programs (or management programs written in other languages, if people
-contribute the language bindings). You can also use it from shell
-scripts or the command line.
+programs (or management programs written in OCaml, Perl, Python, Ruby, Java
+or Haskell). 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
need enough permissions to access the disk images.
-=head1 CONNECTION MANAGEMENT
+Libguestfs is a large API because it can do many things. For a gentle
+introduction, please read the L</API OVERVIEW> section next.
+
+=head1 API OVERVIEW
+
+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.
+
+=head2 HANDLES
-If you are using the high-level API, then you should call the
-functions in the following order:
+Before you can use libguestfs calls, you have to create a handle.
+Then you must add at least one disk image to the handle, followed by
+launching the handle, then performing whatever operations you want,
+and finally closing the handle. So the general structure of all
+libguestfs-using programs looks like this:
guestfs_h *handle = guestfs_create ();
- guestfs_add_drive (handle, "guest.img");
- /* call guestfs_add_drive additional times if the guest has
- * multiple disks
+ /* Call guestfs_add_drive additional times if there are
+ * multiple disk images.
*/
+ guestfs_add_drive (handle, "guest.img");
+ /* Most manipulation calls won't work until you've launched
+ * the handle. You have to do this _after_ adding drives
+ * and _before_ other commands.
+ */
guestfs_launch (handle);
- guestfs_wait_ready (handle);
-
- /* now you can examine what partitions, LVs etc are available
- * you have to mount / at least
- */
+
+ /* Now you can examine what partitions, LVs etc are available.
+ */
+ char **partitions = guestfs_list_partitions (handle);
+ char **logvols = guestfs_lvs (handle);
+
+ /* To access a filesystem in the image, you must mount it.
+ */
guestfs_mount (handle, "/dev/sda1", "/");
-
- /* now you can perform actions on the guest disk image */
+
+ /* Now you can perform filesystem actions on the guest
+ * disk image.
+ */
guestfs_touch (handle, "/hello");
- /* you only need to call guestfs_sync if you have made
- * changes to the guest image
+ /* You only need to call guestfs_sync if you have made
+ * changes to the guest image.
*/
guestfs_sync (handle);
+ /* Close the handle. */
guestfs_close (handle);
-C<guestfs_wait_ready> and all of the actions including C<guestfs_sync>
-are blocking calls. You can use the low-level event API to do
-non-blocking operations instead.
+The code above doesn't include any error checking. In real code you
+should check return values carefully for errors. In general all
+functions that return integers return C<-1> on error, and all
+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.
-All functions that return integers, return C<-1> on error. See
-section ERROR HANDLING below for how to handle errors.
+=head2 DISK IMAGES
-=head2 guestfs_h *
+The image filename (C<"guest.img"> in the example above) could be a
+disk image from a virtual machine, a L<dd(1)> copy of a physical block
+device, an actual block device, or simply an empty file of zeroes that
+you have created through L<posix_fallocate(3)>. Libguestfs lets you
+do useful things to all of these.
-C<guestfs_h> is the opaque type representing a connection handle.
-Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
-to free the handle and release all resources used.
+You can add a disk read-only using C<guestfs_add_drive_ro>, in which
+case libguestfs won't modify the file.
-Handles and operations on handles are not thread safe. However you
-can use a separate handle for each thread (but not on the same disk
-image).
+Be extremely cautious if the disk image is in use, eg. if it is being
+used by a virtual machine. Adding it read-write will almost certainly
+cause disk corruption, but adding it read-only is safe.
-=head2 guestfs_create
+You must add at least one disk image, and you may add multiple disk
+images. In the API, the disk images are usually referred to as
+C</dev/sda> (for the first one you added), C</dev/sdb> (for the second
+one you added), etc.
- guestfs_h *guestfs_create (void);
+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
+names, in the order that you added them. See also L</BLOCK DEVICE
+NAMING> below.
-Create a connection handle.
+=head2 MOUNTING
-You have to call C<guestfs_add_drive> on the handle at least once.
-See CONFIGURATION MANAGEMENT section 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
+image contains (for example) one partition with a filesystem on that
+partition, then you can mount it directly:
-This function returns a non-NULL pointer to a handle on success or
-NULL on error.
+ guestfs_mount (handle, "/dev/sda1", "/");
-After configuring the handle, you have to call C<guestfs_launch> and
-C<guestfs_wait_ready>.
+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>).
-You may also want to configure error handling for the handle. See
-ERROR HANDLING section below.
+If you are given a disk image and you don't know what it contains then
+you have to find out. Libguestfs can also do that: use
+C<guestfs_list_partitions> and C<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)>.
-=head2 guestfs_close
+To mount a disk image read-only, use C<guestfs_mount_ro>. There are
+several other variations of the C<guestfs_mount_*> call.
- void guestfs_close (guestfs_h *handle);
+=head2 FILESYSTEM ACCESS AND MODIFICATION
-This closes the connection handle and frees up all resources used.
+The majority of the libguestfs API consists of fairly low-level calls
+for accessing and modifying the files, directories, symlinks etc on
+mounted filesystems. There are over a hundred such calls which you
+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.
+
+For example, if you mounted a filesystem at C<"/"> and you want to
+read the file called C<"etc/passwd"> then you could do:
+
+ char *data = guestfs_cat (handle, "/etc/passwd");
+
+This would return C<data> as a newly allocated buffer containing the
+full content of that file (with some conditions: see also
+L</DOWNLOADING> below), or C<NULL> if there was an error.
+
+As another example, to create a top-level directory on that filesystem
+called C<"var"> you would do:
+
+ guestfs_mkdir (handle, "/var");
+
+To create a symlink you could do:
+
+ guestfs_ln_s (handle, "/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).
+
+File writes are affected by the per-handle umask, set by calling
+C<guestfs_umask> and defaulting to 022.
+
+=head2 PARTITIONING
+
+Libguestfs contains API calls to read, create and modify partition
+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>
+call:
+
+ const char *parttype = "mbr";
+ if (disk_is_larger_than_2TB)
+ parttype = "gpt";
+ guestfs_part_disk (g, "/dev/sda", parttype);
+
+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
+unless you familiarize yourself with the concepts of physical volumes,
+volume groups and logical volumes.
+
+This author strongly recommends reading the LVM HOWTO, online at
+L<http://tldp.org/HOWTO/LVM-HOWTO/>.
+
+=head2 DOWNLOADING
+
+Use C<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
+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
+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>.
+
+=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 upload a single file, use C<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>.
+
+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
+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
+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.
+
+=head2 LISTING FILES
+
+C<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
+from programs, as a flat list of strings.
+
+C<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.
+
+=head2 RUNNING COMMANDS
+
+Although libguestfs is a primarily an API for manipulating files
+inside guest images, we also provide some limited facilities for
+running commands inside guests.
+
+There are many limitations to this:
+
+=over 4
+
+=item *
+
+The kernel version that the command runs under will be different
+from what it expects.
+
+=item *
+
+If the command needs to communicate with daemons, then most likely
+they won't be running.
+
+=item *
+
+The command will be running in limited memory.
+
+=item *
+
+Only supports Linux guests (not Windows, BSD, etc).
+
+=item *
+
+Architecture limitations (eg. won't work for a PPC guest on
+an X86 host).
+
+=item *
+
+For SELinux guests, you may need to enable SELinux and load policy
+first. See L</SELINUX> in this manpage.
+
+=back
+
+The two main API calls to run commands are C<guestfs_command> and
+C<guestfs_sh> (there are also variations).
+
+The difference is that C<guestfs_sh> runs commands using the shell, so
+any shell globs, redirections, etc will work.
+
+=head2 CONFIGURATION FILES
+
+To read and write configuration files in Linux guest filesystems, we
+strongly recommend using Augeas. For example, Augeas understands how
+to read and write, say, a Linux shadow password file or X.org
+configuration file, and so avoids you having to write that code.
+
+The main Augeas calls are bound through the C<guestfs_aug_*> APIs. We
+don't document Augeas itself here because there is excellent
+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
+you can iterate over.
+
+=head2 SELINUX
+
+We support SELinux guests. To ensure that labeling happens correctly
+in SELinux guests, you need to enable SELinux and load the guest's
+policy:
+
+=over 4
+
+=item 1.
+
+Before launching, do:
+
+ guestfs_set_selinux (g, 1);
+
+=item 2.
+
+After mounting the guest's filesystem(s), load the policy. This
+is best done by running the L<load_policy(8)> command in the
+guest itself:
+
+ guestfs_sh (g, "/usr/sbin/load_policy");
+
+(Older versions of C<load_policy> require you to specify the
+name of the policy file).
+
+=item 3.
+
+Optionally, set the security context for the API. The correct
+security context to use can only be known by inspecting the
+guest. As an example:
+
+ guestfs_setcon (g, "unconfined_u:unconfined_r:unconfined_t:s0");
+
+=back
+
+This will work for running commands and editing existing files.
+
+When new files are created, you may need to label them explicitly,
+for example by running the external command
+C<restorecon pathname>.
+
+=head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS
+
+Libguestfs can mount NTFS partitions. It does this using the
+L<http://www.ntfs-3g.org/> driver.
+
+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)>).
+
+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>.
+
+Libguestfs also provides some help for decoding Windows Registry
+"hive" files, through the library C<libhivex> which is part of
+libguestfs. You have to locate and download the hive file(s)
+yourself, and then pass them to C<libhivex> functions. See also the
+programs L<hivexml(1)>, L<hivexget(1)> and L<virt-win-reg(1)> for more
+help on this issue.
+
+=head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES
-=head2 guestfs_launch, guestfs_wait_ready
+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.
- int guestfs_launch (guestfs_h *handle);
- int guestfs_wait_ready (guestfs_h *handle);
+The API is broadly identical in all supported languages. As an
+example, in Python the handle itself is replaced by an object, but we
+don't try to "object orientify" any other parts of the API.
-Internally libguestfs is implemented by running a virtual machine
-using L<qemu(1)>. These calls are necessary in order to boot the
-virtual machine. More discussion of this is available in the section
-STATE MACHINE AND LOW-LEVEL EVENT API below.
+=over 4
+
+=item B<C++>
+
+You can use the I<guestfs.h> header file from C++ programs. The C++
+API is identical to the C API.
+
+=item B<Haskell>
+
+This is the only language binding that is 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>
+
+Full documentation is contained in the Javadoc which is distributed
+with libguestfs.
+
+=item B<OCaml>
-You should call these two functions after configuring the handle
-(eg. adding drives) but before performing any actions.
+For documentation see the file C<guestfs.mli>.
-=head2 guestfs_kill_subprocess
+=item B<Perl>
- int guestfs_kill_subprocess (guestfs_h *handle);
+For documentation see L<Sys::Guestfs(3)>.
-This kills the qemu subprocess. You should never need to call this.
+=item B<Python>
-=head1 CONFIGURATION MANAGEMENT
+For documentation do:
-The configuration functions allow you to configure which drive images
-will be examined or modified, and set other aspects of the L<qemu(1)>
-virtual machine that we will be running. You need to call only
-C<guestfs_add_drive> at least once for each guest image that you want
-to examine.
+ $ python
+ >>> import guestfs
+ >>> help (guestfs)
-=head2 guestfs_add_drive
+=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.
+
+=item B<shell scripts>
+
+For documentation see L<guestfish(1)>.
+
+=back
+
+=head1 CONNECTION MANAGEMENT
- int guestfs_add_drive (guestfs_h *handle, const char *filename);
+=head2 guestfs_h *
-This function adds a virtual machine disk image C<filename> to the
-guest. The first time you call this function, the disk appears as IDE
-disk 0 (C</dev/sda>) in the guest, the second time as C</dev/sdb>, and
-so on.
+C<guestfs_h> is the opaque type representing a connection handle.
+Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
+to free the handle and release all resources used.
-You don't necessarily need to be root when using libguestfs. However
-you obviously do need sufficient permissions to access the filename
-for whatever operations you want to perform (ie. read access if you
-just want to read the image or write access if you want to modify the
-image).
+For information on using multiple handles and threads, see the section
+L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
-This is equivalent to the qemu parameter C<-drive file=filename>.
+=head2 guestfs_create
-=head2 guestfs_add_cdrom
+ guestfs_h *guestfs_create (void);
- int guestfs_add_cdrom (guestfs_h *handle, const char *filename);
+Create a connection handle.
-This function adds a virtual CD-ROM disk image to the guest.
+You have to call C<guestfs_add_drive> on the handle at least once.
-This is equivalent to the qemu parameter C<-cdrom filename>.
+This function returns a non-NULL pointer to a handle on success or
+NULL on error.
-=head2 guestfs_config
+After configuring the handle, you have to call C<guestfs_launch>.
- int guestfs_config (guestfs_h *handle,
- const char *qemu_param, const char *qemu_value);
+You may also want to configure error handling for the handle. See
+L</ERROR HANDLING> section below.
-This can be used to add arbitrary qemu command line parameters
-of the form C<-param value>. Actually it's not quite arbitrary - we
-prevent you from setting some parameters which would interfere with
-parameters that we use.
+=head2 guestfs_close
-The first character of C<qemu_param> string must be a C<-> (dash).
+ void guestfs_close (guestfs_h *handle);
-C<qemu_value> can be NULL.
+This closes the connection handle and frees up all resources used.
=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_set_error_handler>. The default error
-handler prints the information string to C<stderr>.
+errors by calling C<guestfs_last_error> and/or by setting up an error
+handler with C<guestfs_set_error_handler>.
+
+The default error handler prints the information string to C<stderr>.
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>.
+=head2 guestfs_last_error
+
+ const char *guestfs_last_error (guestfs_h *handle);
+
+This returns the last error message that happened on C<handle>. 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
+C<guestfs_close> is called.
+
+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 guestfs_set_error_handler
typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
parameters passed to the callback are an opaque data pointer and the
error message string.
+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 and the error
-message is completely discarded.
+If you set C<cb> to C<NULL> then I<no> handler is called.
=head2 guestfs_get_error_handler
Returns the current error handler callback.
-=head2 guestfs_set_out_of_memory_handler
+=head2 guestfs_set_out_of_memory_handler
typedef void (*guestfs_abort_cb) (void);
int guestfs_set_out_of_memory_handler (guestfs_h *handle,
This returns the current out of memory handler.
-=head1 VERBOSE MESSAGES
-
-=head2 guestfs_set_verbose
-
- void guestfs_set_verbose (guestfs_h *handle, int verbose);
+=head1 PATH
-If C<verbose> is true, this turns on verbose messages (to C<stderr>).
+Libguestfs needs a kernel and initrd.img, which it finds by looking
+along an internal path.
-Verbose messages are disabled unless the environment variable
-C<LIBGUESTFS_DEBUG> is defined and set to C<1>.
+By default it looks for these in the directory C<$libdir/guestfs>
+(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
-=head2 guestfs_get_verbose
-
- int guestfs_get_verbose (guestfs_h *handle);
-
-This returns the verbose messages flag.
+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.
+@ACTIONS@
+=head1 STRUCTURES
-
-
-
-
+@STRUCTS@
=head1 STATE MACHINE AND LOW-LEVEL EVENT API
/ | | LAUNCHING |
/ | \___________/
/ | /
- / | guestfs_wait_ready
+ / | guestfs_launch
/ | /
______ / __|____V
/ \ ------> / \
be issued when in the CONFIG state.
The high-level API offers two calls that go from CONFIG through
-LAUNCHING to READY. C<guestfs_launch> is a non-blocking call that
-starts up the child process, immediately moving from CONFIG to
-LAUNCHING. C<guestfs_wait_ready> blocks until the child process is
-READY to accept commands (or until some failure or timeout). The
-low-level event API described below provides a non-blocking way to
-replace C<guestfs_wait_ready>.
+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.
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
=head2 SETTING CALLBACKS TO HANDLE EVENTS
The child process generates events in some situations. Current events
-include: receiving a reply message after some action, receiving a log
-message, the child process exits, &c.
+include: receiving a log message, the child process exits.
Use the C<guestfs_set_*_callback> functions to set a callback for
different types of events.
callback of that type. Cancel all callbacks of this type by calling
this function with C<cb> set to C<NULL>.
-=head2 NON-BLOCKING ACTIONS
-
-XXX NOT IMPLEMENTED YET XXX
-
-C<guestfs_set_reply_callback> is the most interesting callback to
-play with, since it allows you to perform actions without blocking.
-
-For example:
-
- do_it ()
- {
- start_call ();
- guestfs_main_loop_run (); /* --> blocks, then calls my_cb */
- }
-
- start_call ()
- {
- guestfs_set_reply_callback (handle, my_cb, data);
- guestfs_nb_[action] (handle, [other parameters ...]);
- /* returns immediately */
- }
-
- my_cb (guestfs_h *handle, void *data, XDR *xdr)
- {
- retval = guestfs_nb_[action]_r (handle, xdr);
- /* ... */
- }
-
-There are C<guestfs_nb_*> and C<guestfs_nb_*_r> functions
-corresponding to every C<guestfs_*> action in the high-level API.
-
-=head2 guestfs_set_reply_callback
-
- typedef void (*guestfs_reply_cb) (guestfs_h *g, void *opaque, XDR *xdr);
- void guestfs_set_reply_callback (guestfs_h *handle,
- guestfs_reply_cb cb,
- void *opaque);
-
-The callback function C<cb> will be called whenever a reply is
-received from the child process. (This corresponds to a transition
-from the BUSY state to the READY state).
-
-Note that the C<xdr> that you get in the callback is in C<XDR_DECODE>
-mode, and you need to consume it before you return from the callback
-function (since it gets destroyed after).
-
=head2 guestfs_set_log_message_callback
typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
becomes ready first time after it has been launched. (This
corresponds to a transition from LAUNCHING to the READY state).
-You can use this instead of C<guestfs_wait_ready> to implement a
-non-blocking wait for the child process to finish booting up.
+=head1 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
+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.
+
+=head2 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 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 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.
+
+=over 4
+
+=item *
-=head2 EVENT MAIN LOOP
+Is the string a parameter which is a device or partition name?
-To use the low-level event API, you have to provide an event "main
-loop". You can write your own, but if you don't want to write one,
-two are provided for you:
+=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
+
+=head2 PORTABILITY CONCERNS
+
+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 libguestfs-select
+=item *
-A simple main loop that is implemented using L<select(2)>.
+Use C<guestfs_list_devices> or C<guestfs_list_partitions> to list
+actual device names, and then use those names directly.
-This is the default main loop unless you call C<guestfs_set_main_loop>
-or C<guestfs_glib_set_main_loop>.
+Since those device names exist by definition, they will never be
+translated.
-=item libguestfs-glib
+=item *
-An implementation which can be used with GLib and GTK+ programs. You
-can use this to write graphical (GTK+) programs which use libguestfs
-without hanging during long or slow operations.
+Use higher level ways to identify filesystems, such as LVM names,
+UUIDs and filesystem labels.
=back
-=head2 guestfs_set_main_loop
+=head1 INTERNALS
- void guestfs_set_main_loop (guestfs_main_loop *);
+=head2 COMMUNICATION PROTOCOL
-This call sets the current main loop to the list of callbacks
-contained in the C<guestfs_main_loop> structure.
+Don't rely on using this protocol directly. This section documents
+how it currently works, but it may change at any time.
-Only one main loop implementation can be used by libguestfs, so
-calling this replaces the previous one. (So this is something that
-has to be done by the main program, but only the main program "knows"
-that it is a GTK+ program or whatever).
+The protocol used to talk between the library and the daemon running
+inside the qemu virtual machine is a simple RPC mechanism built on top
+of XDR (RFC 1014, RFC 1832, RFC 4506).
-You should call this early in the main program, certainly before
-calling C<guestfs_create>.
+The detailed format of structures is in C<src/guestfs_protocol.x>
+(note: this file is automatically generated).
-=head2 guestfs_glib_set_main_loop
+There are two broad cases, ordinary functions that don't have any
+C<FileIn> and C<FileOut> parameters, which are handled with very
+simple request/reply messages. Then there are functions that have any
+C<FileIn> or C<FileOut> parameters, which use the same request and
+reply messages, but they may also be followed by files sent using a
+chunked encoding.
- void guestfs_glib_set_main_loop (GMainLoop *);
+=head3 ORDINARY FUNCTIONS (NO FILEIN/FILEOUT PARAMS)
-This helper calls C<guestfs_set_main_loop> with the correct callbacks
-for integrating with the GLib main loop.
+For ordinary functions, the request message is:
-The libguestfs-glib main loop is contained in a separate library, so
-that libguestfs doesn't depend on the whole of GLib:
+ total length (header + arguments,
+ but not including the length word itself)
+ struct guestfs_message_header (encoded as XDR)
+ struct guestfs_<foo>_args (encoded as XDR)
- #include <glib.h>
- #include <guestfs-glib.h>
+The total length field allows the daemon to allocate a fixed size
+buffer into which it slurps the rest of the message. As a result, the
+total length is limited to C<GUESTFS_MESSAGE_MAX> bytes (currently
+4MB), which means the effective size of any request is limited to
+somewhere under this size.
- main ()
- {
- GMainLoop *loop =
- g_main_loop_new (g_main_context_default (), 1);
- ...
- guestfs_glib_set_main_loop (loop);
+Note also that many functions don't take any arguments, in which case
+the C<guestfs_I<foo>_args> is completely omitted.
+
+The header contains the procedure number (C<guestfs_proc>) which is
+how the receiver knows what type of args structure to expect, or none
+at all.
+
+The reply message for ordinary functions is:
+
+ total length (header + ret,
+ but not including the length word itself)
+ struct guestfs_message_header (encoded as XDR)
+ struct guestfs_<foo>_ret (encoded as XDR)
+
+As above the C<guestfs_I<foo>_ret> structure may be completely omitted
+for functions that return no formal return values.
+
+As above the total length of the reply is limited to
+C<GUESTFS_MESSAGE_MAX>.
+
+In the case of an error, a flag is set in the header, and the reply
+message is slightly changed:
+
+ total length (header + error,
+ but not including the length word itself)
+ struct guestfs_message_header (encoded as XDR)
+ struct guestfs_message_error (encoded as XDR)
+
+The C<guestfs_message_error> structure contains the error message as a
+string.
+
+=head3 FUNCTIONS THAT HAVE FILEIN PARAMETERS
+
+A C<FileIn> parameter indicates that we transfer a file I<into> the
+guest. The normal request message is sent (see above). However this
+is followed by a sequence of file chunks.
+
+ total length (header + arguments,
+ but not including the length word itself,
+ and not including the chunks)
+ struct guestfs_message_header (encoded as XDR)
+ struct guestfs_<foo>_args (encoded as XDR)
+ sequence of chunks for FileIn param #0
+ sequence of chunks for FileIn param #1 etc.
+
+The "sequence of chunks" is:
+
+ length of chunk (not including length word itself)
+ struct guestfs_chunk (encoded as XDR)
+ length of chunk
+ struct guestfs_chunk (encoded as XDR)
...
- g_main_loop_run (loop);
- }
+ length of chunk
+ struct guestfs_chunk (with data.data_len == 0)
+
+The final chunk has the C<data_len> field set to zero. Additionally a
+flag is set in the final chunk to indicate either successful
+completion or early cancellation.
+
+At time of writing there are no functions that have more than one
+FileIn parameter. However this is (theoretically) supported, by
+sending the sequence of chunks for each FileIn parameter one after
+another (from left to right).
+
+Both the library (sender) I<and> the daemon (receiver) may cancel the
+transfer. The library does this by sending a chunk with a special
+flag set to indicate cancellation. When the daemon sees this, it
+cancels the whole RPC, does I<not> send any reply, and goes back to
+reading the next request.
+
+The daemon may also cancel. It does this by writing a special word
+C<GUESTFS_CANCEL_FLAG> to the socket. The library listens for this
+during the transfer, and if it gets it, it will cancel the transfer
+(it sends a cancel chunk). The special word is chosen so that even if
+cancellation happens right at the end of the transfer (after the
+library has finished writing and has started listening for the reply),
+the "spurious" cancel flag will not be confused with the reply
+message.
+
+This protocol allows the transfer of arbitrary sized files (no 32 bit
+limit), and also files where the size is not known in advance
+(eg. from pipes or sockets). However the chunks are rather small
+(C<GUESTFS_MAX_CHUNK_SIZE>), so that neither the library nor the
+daemon need to keep much in memory.
+
+=head3 FUNCTIONS THAT HAVE FILEOUT PARAMETERS
+
+The protocol for FileOut parameters is exactly the same as for FileIn
+parameters, but with the roles of daemon and library reversed.
+
+ total length (header + ret,
+ but not including the length word itself,
+ and not including the chunks)
+ struct guestfs_message_header (encoded as XDR)
+ struct guestfs_<foo>_ret (encoded as XDR)
+ sequence of chunks for FileOut param #0
+ sequence of chunks for FileOut param #1 etc.
+
+=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.
+
+=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.
+
+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.
+
+=head1 ENVIRONMENT VARIABLES
+
+=over 4
+
+=item LIBGUESTFS_APPEND
+
+Pass additional options to the guest kernel.
-To use this main loop you must link with C<-lguestfs-glib>. (See also
-the GLib and GTK+ documentation).
+=item LIBGUESTFS_DEBUG
-=head2 guestfs_main_loop_run
+Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
+has the same effect as calling C<guestfs_set_verbose (handle, 1)>.
- void guestfs_main_loop_run (void);
+=item LIBGUESTFS_MEMSIZE
-This calls the main loop.
+Set the memory allocated to the qemu process, in megabytes. For
+example:
-For some types of main loop you may want or prefer to call another
-function, eg. C<g_main_loop_run>, or the main loop may already be
-invoked by another part of your program. In those cases, ignore this
-call.
+ LIBGUESTFS_MEMSIZE=700
-=head2 guestfs_main_loop_quit
+=item LIBGUESTFS_PATH
- void guestfs_main_loop_quit (void);
+Set the path that libguestfs uses to search for kernel and initrd.img.
+See the discussion of paths in section PATH above.
-This instructs the main loop to quit. In other words,
-C<guestfs_main_loop_run> will return.
+=item LIBGUESTFS_QEMU
-For some types of main loop you may want or prefer to call another
-function, eg. C<g_main_loop_quit>. In those cases, ignore this call.
+Set the default qemu binary that libguestfs uses. If not set, then
+the qemu which was found at compile time by the configure script is
+used.
-=head2 WRITING A CUSTOM MAIN LOOP
+See also L</QEMU WRAPPERS> above.
-This isn't documented. Please see the libguestfs-select and
-libguestfs-glib implementations.
+=item LIBGUESTFS_TRACE
+
+Set C<LIBGUESTFS_TRACE=1> to enable command traces. This
+has the same effect as calling C<guestfs_set_trace (handle, 1)>.
+
+=item TMPDIR
+
+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
+configure another directory to use in case C</tmp> is not large
+enough.
+
+=back
=head1 SEE ALSO
-L<qemu(1)>
+L<guestfish(1)>,
+L<qemu(1)>,
+L<febootstrap(1)>,
+L<http://libguestfs.org/>.
+
+Tools with a similar purpose:
+L<fdisk(8)>,
+L<parted(8)>,
+L<kpartx(8)>,
+L<lvm(8)>,
+L<disktype(1)>.
+=head1 BUGS
+To get a list of bugs against libguestfs use this link:
+L<https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools>
+To report a new bug against libguestfs use this link:
+
+L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
+
+When reporting a bug, please check:
+
+=over 4
+
+=item *
+
+That the bug hasn't been reported already.
+
+=item *
+
+That you are testing a recent version.
+
+=item *
+
+Describe the bug accurately, and give a way to reproduce it.
+
+=item *
+
+Run libguestfs-test-tool and paste the B<complete, unedited>
+output into the bug report.
+
+=back
=head1 AUTHORS
=head1 COPYRIGHT
Copyright (C) 2009 Red Hat Inc.
-L<http://et.redhat.com/~rjones/libguestfs>
+L<http://libguestfs.org/>
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
git.annexia.org / libguestfs.git / blobdiff