5 guestfs - Library for accessing and modifying virtual machine images
11 guestfs_h *handle = guestfs_create ();
12 guestfs_add_drive (handle, "guest.img");
13 guestfs_launch (handle);
14 guestfs_wait_ready (handle);
15 guestfs_mount (handle, "/dev/sda1", "/");
16 guestfs_touch (handle, "/hello");
17 guestfs_sync (handle);
18 guestfs_close (handle);
22 Libguestfs is a library for accessing and modifying guest disk images.
23 Amongst the things this is good for: making batch configuration
24 changes to guests, getting disk used/free statistics (see also:
25 virt-df), migrating between virtualization systems (see also:
26 virt-p2v), performing partial backups, performing partial guest
27 clones, cloning guests and changing registry/UUID/hostname info, and
30 Libguestfs uses Linux kernel and qemu code, and can access any type of
31 guest filesystem that Linux and qemu can, including but not limited
32 to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
33 schemes, qcow, qcow2, vmdk.
35 Libguestfs provides ways to enumerate guest storage (eg. partitions,
36 LVs, what filesystem is in each LV, etc.). It can also run commands
37 in the context of the guest. Also you can mount guest filesystems on
38 the host (requires root privs and NFS).
40 Libguestfs is a library that can be linked with C and C++ management
41 programs (or management programs written in other languages, if people
42 contribute the language bindings). You can also use it from shell
43 scripts or the command line.
45 You don't need to be root to use libguestfs, although obviously you do
46 need enough permissions to access the disk images.
48 =head1 CONNECTION MANAGEMENT
50 If you are using the high-level API, then you should call the
51 functions in the following order:
53 guestfs_h *handle = guestfs_create ();
55 guestfs_add_drive (handle, "guest.img");
56 /* call guestfs_add_drive additional times if the guest has
60 guestfs_launch (handle);
61 guestfs_wait_ready (handle);
63 /* now you can examine what partitions, LVs etc are available
64 * you have to mount / at least
66 guestfs_mount (handle, "/dev/sda1", "/");
68 /* now you can perform actions on the guest disk image */
69 guestfs_touch (handle, "/hello");
71 /* you only need to call guestfs_sync if you have made
72 * changes to the guest image
74 guestfs_sync (handle);
76 guestfs_close (handle);
78 C<guestfs_wait_ready> and all of the actions including C<guestfs_sync>
79 are blocking calls. You can use the low-level event API to do
80 non-blocking operations instead.
82 All functions that return integers, return C<-1> on error. See
83 section ERROR HANDLING below for how to handle errors.
87 C<guestfs_h> is the opaque type representing a connection handle.
88 Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
89 to free the handle and release all resources used.
91 Handles and operations on handles are not thread safe. However you
92 can use a separate handle for each thread (but not on the same disk
97 guestfs_h *guestfs_create (void);
99 Create a connection handle.
101 You have to call C<guestfs_add_drive> on the handle at least once.
102 See CONFIGURATION MANAGEMENT section below.
104 This function returns a non-NULL pointer to a handle on success or
107 After configuring the handle, you have to call C<guestfs_launch> and
108 C<guestfs_wait_ready>.
110 You may also want to configure error handling for the handle. See
111 ERROR HANDLING section below.
115 void guestfs_close (guestfs_h *handle);
117 This closes the connection handle and frees up all resources used.
119 =head2 guestfs_launch, guestfs_wait_ready
121 int guestfs_launch (guestfs_h *handle);
122 int guestfs_wait_ready (guestfs_h *handle);
124 Internally libguestfs is implemented by running a virtual machine
125 using L<qemu(1)>. These calls are necessary in order to boot the
126 virtual machine. More discussion of this is available in the section
127 STATE MACHINE AND LOW-LEVEL EVENT API below.
129 You should call these two functions after configuring the handle
130 (eg. adding drives) but before performing any actions.
132 =head2 guestfs_kill_subprocess
134 int guestfs_kill_subprocess (guestfs_h *handle);
136 This kills the qemu subprocess. You should never need to call this.
138 =head1 CONFIGURATION MANAGEMENT
140 The configuration functions allow you to configure which drive images
141 will be examined or modified, and set other aspects of the L<qemu(1)>
142 virtual machine that we will be running. You need to call only
143 C<guestfs_add_drive> at least once for each guest image that you want
146 =head2 guestfs_add_drive
148 int guestfs_add_drive (guestfs_h *handle, const char *filename);
150 This function adds a virtual machine disk image C<filename> to the
151 guest. The first time you call this function, the disk appears as IDE
152 disk 0 (C</dev/sda>) in the guest, the second time as C</dev/sdb>, and
155 You don't necessarily need to be root when using libguestfs. However
156 you obviously do need sufficient permissions to access the filename
157 for whatever operations you want to perform (ie. read access if you
158 just want to read the image or write access if you want to modify the
161 This is equivalent to the qemu parameter C<-drive file=filename>.
163 =head2 guestfs_add_cdrom
165 int guestfs_add_cdrom (guestfs_h *handle, const char *filename);
167 This function adds a virtual CD-ROM disk image to the guest.
169 This is equivalent to the qemu parameter C<-cdrom filename>.
171 =head2 guestfs_config
173 int guestfs_config (guestfs_h *handle,
174 const char *qemu_param, const char *qemu_value);
176 This can be used to add arbitrary qemu command line parameters
177 of the form C<-param value>. Actually it's not quite arbitrary - we
178 prevent you from setting some parameters which would interfere with
179 parameters that we use.
181 The first character of C<qemu_param> string must be a C<-> (dash).
183 C<qemu_value> can be NULL.
185 =head1 ERROR HANDLING
187 The convention in all functions that return C<int> is that they return
188 C<-1> to indicate an error. You can get additional information on
189 errors by calling C<guestfs_set_error_handler>. The default error
190 handler prints the information string to C<stderr>.
192 Out of memory errors are handled differently. The default action is
193 to call L<abort(3)>. If this is undesirable, then you can set a
194 handler using C<guestfs_set_out_of_memory_handler>.
196 =head2 guestfs_set_error_handler
198 typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
201 void guestfs_set_error_handler (guestfs_h *handle,
202 guestfs_error_handler_cb cb,
205 The callback C<cb> will be called if there is an error. The
206 parameters passed to the callback are an opaque data pointer and the
207 error message string.
209 The default handler prints messages on C<stderr>.
211 If you set C<cb> to C<NULL> then I<no> handler is called and the error
212 message is completely discarded.
214 =head2 guestfs_get_error_handler
216 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
219 Returns the current error handler callback.
221 =head2 guestfs_set_out_of_memory_handler
223 typedef void (*guestfs_abort_cb) (void);
224 int guestfs_set_out_of_memory_handler (guestfs_h *handle,
227 The callback C<cb> will be called if there is an out of memory
228 situation. I<Note this callback must not return>.
230 The default is to call L<abort(3)>.
232 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
235 =head2 guestfs_get_out_of_memory_handler
237 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
239 This returns the current out of memory handler.
241 =head1 VERBOSE MESSAGES
243 =head2 guestfs_set_verbose
245 void guestfs_set_verbose (guestfs_h *handle, int verbose);
247 If C<verbose> is true, this turns on verbose messages (to C<stderr>).
249 Verbose messages are disabled unless the environment variable
250 C<LIBGUESTFS_DEBUG> is defined and set to C<1>.
252 =head2 guestfs_get_verbose
254 int guestfs_get_verbose (guestfs_h *handle);
256 This returns the verbose messages flag.
258 =head1 HIGH-LEVEL API ACTIONS
269 =head1 STATE MACHINE AND LOW-LEVEL EVENT API
271 Internally, libguestfs is implemented by running a virtual machine
272 using L<qemu(1)>. QEmu runs as a child process of the main program,
273 and most of this discussion won't make sense unless you understand
274 that the complexity is dealing with the (asynchronous) actions of the
278 ___________________ _________________________
280 | main program | | qemu +-----------------+|
281 | | | | Linux kernel ||
282 +-------------------+ | +-----------------+|
283 | libguestfs <-------------->| guestfsd ||
284 | | | +-----------------+|
285 \___________________/ \_________________________/
287 The diagram above shows libguestfs communicating with the guestfsd
288 daemon running inside the qemu child process. There are several
289 points of failure here: qemu can fail to start, the virtual machine
290 inside qemu can fail to boot, guestfsd can fail to start or not
291 establish communication, any component can start successfully but fail
292 asynchronously later, and so on.
296 libguestfs uses a state machine to model the child process:
307 / | \ \ guestfs_launch
313 / | guestfs_wait_ready
318 \______/ <------ \________/
320 The normal transitions are (1) CONFIG (when the handle is created, but
321 there is no child process), (2) LAUNCHING (when the child process is
322 booting up), (3) alternating between READY and BUSY as commands are
323 issued to, and carried out by, the child process.
325 The guest may be killed by C<guestfs_kill_subprocess>, or may die
326 asynchronously at any time (eg. due to some internal error), and that
327 causes the state to transition back to CONFIG.
329 Configuration commands for qemu such as C<guestfs_add_drive> can only
330 be issued when in the CONFIG state.
332 The high-level API offers two calls that go from CONFIG through
333 LAUNCHING to READY. C<guestfs_launch> is a non-blocking call that
334 starts up the child process, immediately moving from CONFIG to
335 LAUNCHING. C<guestfs_wait_ready> blocks until the child process is
336 READY to accept commands (or until some failure or timeout). The
337 low-level event API described below provides a non-blocking way to
338 replace C<guestfs_wait_ready>.
340 High-level API actions such as C<guestfs_mount> can only be issued
341 when in the READY state. These high-level API calls block waiting for
342 the command to be carried out (ie. the state to transition to BUSY and
343 then back to READY). But using the low-level event API, you get
344 non-blocking versions. (But you can still only carry out one
345 operation per handle at a time - that is a limitation of the
346 communications protocol we use).
348 Finally, the child process sends asynchronous messages back to the
349 main program, such as kernel log messages. Mostly these are ignored
350 by the high-level API, but using the low-level event API you can
351 register to receive these messages.
353 =head2 SETTING CALLBACKS TO HANDLE EVENTS
355 The child process generates events in some situations. Current events
356 include: receiving a reply message after some action, receiving a log
357 message, the child process exits, &c.
359 Use the C<guestfs_set_*_callback> functions to set a callback for
360 different types of events.
362 Only I<one callback of each type> can be registered for each handle.
363 Calling C<guestfs_set_*_callback> again overwrites the previous
364 callback of that type. Cancel all callbacks of this type by calling
365 this function with C<cb> set to C<NULL>.
367 =head2 NON-BLOCKING ACTIONS
369 C<guestfs_set_reply_callback> is the most interesting callback to
370 play with, since it allows you to perform actions without blocking.
377 guestfs_main_loop_run (); /* --> blocks, then calls my_cb */
382 guestfs_set_reply_callback (handle, my_cb, data);
383 guestfs_nb_[action] (handle, [other parameters ...]);
384 /* returns immediately */
387 my_cb (guestfs_h *handle, void *data, XDR *xdr)
389 retval = guestfs_nb_[action]_r (handle, xdr);
393 There are C<guestfs_nb_*> and C<guestfs_nb_*_r> functions
394 corresponding to (very nearly) every C<guestfs_*> action in the
397 =head2 guestfs_set_reply_callback
399 typedef void (*guestfs_reply_cb) (guestfs_h *g, void *opaque, XDR *xdr);
400 void guestfs_set_reply_callback (guestfs_h *handle,
404 The callback function C<cb> will be called whenever a reply is
405 received from the child process. (This corresponds to a transition
406 from the BUSY state to the READY state).
408 Note that the C<xdr> that you get in the callback is in C<XDR_DECODE>
409 mode, and you need to consume it before you return from the callback
410 function (since it gets destroyed after).
412 =head2 guestfs_set_log_message_callback
414 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
416 void guestfs_set_log_message_callback (guestfs_h *handle,
417 guestfs_log_message_cb cb,
420 The callback function C<cb> will be called whenever qemu or the guest
421 writes anything to the console.
423 Use this function to capture kernel messages and similar.
425 Normally there is no log message handler, and log messages are just
428 =head2 guestfs_set_subprocess_quit_callback
430 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
431 void guestfs_set_subprocess_quit_callback (guestfs_h *handle,
432 guestfs_subprocess_quit_cb cb,
435 The callback function C<cb> will be called when the child process
436 quits, either asynchronously or if killed by
437 C<guestfs_kill_subprocess>. (This corresponds to a transition from
438 any state to the CONFIG state).
440 =head2 guestfs_set_launch_done_callback
442 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
443 void guestfs_set_launch_done_callback (guestfs_h *handle,
447 The callback function C<cb> will be called when the child process
448 becomes ready first time after it has been launched. (This
449 corresponds to a transition from LAUNCHING to the READY state).
451 You can use this instead of C<guestfs_wait_ready> to implement a
452 non-blocking wait for the child process to finish booting up.
454 =head2 EVENT MAIN LOOP
456 To use the low-level event API, you have to provide an event "main
457 loop". You can write your own, but if you don't want to write one,
458 two are provided for you:
462 =item libguestfs-select
464 A simple main loop that is implemented using L<select(2)>.
466 This is the default main loop unless you call C<guestfs_set_main_loop>
467 or C<guestfs_glib_set_main_loop>.
469 =item libguestfs-glib
471 An implementation which can be used with GLib and GTK+ programs. You
472 can use this to write graphical (GTK+) programs which use libguestfs
473 without hanging during long or slow operations.
477 =head2 guestfs_set_main_loop
479 void guestfs_set_main_loop (guestfs_main_loop *);
481 This call sets the current main loop to the list of callbacks
482 contained in the C<guestfs_main_loop> structure.
484 Only one main loop implementation can be used by libguestfs, so
485 calling this replaces the previous one. (So this is something that
486 has to be done by the main program, but only the main program "knows"
487 that it is a GTK+ program or whatever).
489 You should call this early in the main program, certainly before
490 calling C<guestfs_create>.
492 =head2 guestfs_glib_set_main_loop
494 void guestfs_glib_set_main_loop (GMainLoop *);
496 This helper calls C<guestfs_set_main_loop> with the correct callbacks
497 for integrating with the GLib main loop.
499 The libguestfs-glib main loop is contained in a separate library, so
500 that libguestfs doesn't depend on the whole of GLib:
503 #include <guestfs-glib.h>
508 g_main_loop_new (g_main_context_default (), 1);
510 guestfs_glib_set_main_loop (loop);
512 g_main_loop_run (loop);
515 To use this main loop you must link with C<-lguestfs-glib>. (See also
516 the GLib and GTK+ documentation).
518 =head2 guestfs_main_loop_run
520 void guestfs_main_loop_run (void);
522 This calls the main loop.
524 For some types of main loop you may want or prefer to call another
525 function, eg. C<g_main_loop_run>, or the main loop may already be
526 invoked by another part of your program. In those cases, ignore this
529 =head2 guestfs_main_loop_quit
531 void guestfs_main_loop_quit (void);
533 This instructs the main loop to quit. In other words,
534 C<guestfs_main_loop_run> will return.
536 For some types of main loop you may want or prefer to call another
537 function, eg. C<g_main_loop_quit>. In those cases, ignore this call.
539 =head2 WRITING A CUSTOM MAIN LOOP
541 This isn't documented. Please see the libguestfs-select and
542 libguestfs-glib implementations.
554 Richard W.M. Jones (C<rjones at redhat dot com>)
558 Copyright (C) 2009 Red Hat Inc.
559 L<http://et.redhat.com/~rjones/libguestfs>
561 This library is free software; you can redistribute it and/or
562 modify it under the terms of the GNU Lesser General Public
563 License as published by the Free Software Foundation; either
564 version 2 of the License, or (at your option) any later version.
566 This library is distributed in the hope that it will be useful,
567 but WITHOUT ANY WARRANTY; without even the implied warranty of
568 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
569 Lesser General Public License for more details.
571 You should have received a copy of the GNU Lesser General Public
572 License along with this library; if not, write to the Free Software
573 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA