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 access filesystems over FTP.
39 Libguestfs is a library that can be linked with C and C++ management
40 programs (or management programs written in other languages, if people
41 contribute the language bindings). You can also use it from shell
42 scripts or the command line.
44 You don't need to be root to use libguestfs, although obviously you do
45 need enough permissions to access the disk images.
47 =head1 CONNECTION MANAGEMENT
49 If you are using the high-level API, then you should call the
50 functions in the following order:
52 guestfs_h *handle = guestfs_create ();
54 guestfs_add_drive (handle, "guest.img");
55 /* call guestfs_add_drive additional times if the guest has
59 guestfs_launch (handle);
60 guestfs_wait_ready (handle);
62 /* now you can examine what partitions, LVs etc are available
63 * you have to mount / at least
65 guestfs_mount (handle, "/dev/sda1", "/");
67 /* now you can perform actions on the guest disk image */
68 guestfs_touch (handle, "/hello");
70 /* you only need to call guestfs_sync if you have made
71 * changes to the guest image
73 guestfs_sync (handle);
75 guestfs_close (handle);
77 C<guestfs_wait_ready> and all of the actions including C<guestfs_sync>
78 are blocking calls. You can use the low-level event API to do
79 non-blocking operations instead.
81 All functions that return integers, return C<-1> on error. See
82 section ERROR HANDLING below for how to handle errors.
86 C<guestfs_h> is the opaque type representing a connection handle.
87 Create a handle by calling C<guestfs_create>. Call C<guestfs_close>
88 to free the handle and release all resources used.
90 Handles and operations on handles are not thread safe. However you
91 can use a separate handle for each thread (but not on the same disk
96 guestfs_h *guestfs_create (void);
98 Create a connection handle.
100 You have to call C<guestfs_add_drive> on the handle at least once.
101 See CONFIGURATION MANAGEMENT section below.
103 This function returns a non-NULL pointer to a handle on success or
106 After configuring the handle, you have to call C<guestfs_launch> and
107 C<guestfs_wait_ready>.
109 You may also want to configure error handling for the handle. See
110 ERROR HANDLING section below.
114 void guestfs_close (guestfs_h *handle);
116 This closes the connection handle and frees up all resources used.
118 =head2 guestfs_launch, guestfs_wait_ready
120 int guestfs_launch (guestfs_h *handle);
121 int guestfs_wait_ready (guestfs_h *handle);
123 Internally libguestfs is implemented by running a virtual machine
124 using L<qemu(1)>. These calls are necessary in order to boot the
125 virtual machine. More discussion of this is available in the section
126 STATE MACHINE AND LOW-LEVEL EVENT API below.
128 You should call these two functions after configuring the handle
129 (eg. adding drives) but before performing any actions.
131 =head2 guestfs_kill_subprocess
133 int guestfs_kill_subprocess (guestfs_h *handle);
135 This kills the qemu subprocess. You should never need to call this.
137 =head1 CONFIGURATION MANAGEMENT
139 The configuration functions allow you to configure which drive images
140 will be examined or modified, and set other aspects of the L<qemu(1)>
141 virtual machine that we will be running. You need to call only
142 C<guestfs_add_drive> at least once for each guest image that you want
145 =head2 guestfs_add_drive
147 int guestfs_add_drive (guestfs_h *handle, const char *filename);
149 This function adds a virtual machine disk image C<filename> to the
150 guest. The first time you call this function, the disk appears as IDE
151 disk 0 (C</dev/sda>) in the guest, the second time as C</dev/sdb>, and
154 You don't necessarily need to be root when using libguestfs. However
155 you obviously do need sufficient permissions to access the filename
156 for whatever operations you want to perform (ie. read access if you
157 just want to read the image or write access if you want to modify the
160 This is equivalent to the qemu parameter C<-drive file=filename>.
162 =head2 guestfs_add_cdrom
164 int guestfs_add_cdrom (guestfs_h *handle, const char *filename);
166 This function adds a virtual CD-ROM disk image to the guest.
168 This is equivalent to the qemu parameter C<-cdrom filename>.
170 =head2 guestfs_config
172 int guestfs_config (guestfs_h *handle,
173 const char *qemu_param, const char *qemu_value);
175 This can be used to add arbitrary qemu command line parameters
176 of the form C<-param value>. Actually it's not quite arbitrary - we
177 prevent you from setting some parameters which would interfere with
178 parameters that we use.
180 The first character of C<qemu_param> string must be a C<-> (dash).
182 C<qemu_value> can be NULL.
184 =head1 ERROR HANDLING
186 The convention in all functions that return C<int> is that they return
187 C<-1> to indicate an error. You can get additional information on
188 errors by calling C<guestfs_set_error_handler>. The default error
189 handler prints the information string to C<stderr>.
191 Out of memory errors are handled differently. The default action is
192 to call L<abort(3)>. If this is undesirable, then you can set a
193 handler using C<guestfs_set_out_of_memory_handler>.
195 =head2 guestfs_set_error_handler
197 typedef void (*guestfs_error_handler_cb) (guestfs_h *handle,
200 void guestfs_set_error_handler (guestfs_h *handle,
201 guestfs_error_handler_cb cb,
204 The callback C<cb> will be called if there is an error. The
205 parameters passed to the callback are an opaque data pointer and the
206 error message string.
208 The default handler prints messages on C<stderr>.
210 If you set C<cb> to C<NULL> then I<no> handler is called and the error
211 message is completely discarded.
213 =head2 guestfs_get_error_handler
215 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
218 Returns the current error handler callback.
220 =head2 guestfs_set_out_of_memory_handler
222 typedef void (*guestfs_abort_cb) (void);
223 int guestfs_set_out_of_memory_handler (guestfs_h *handle,
226 The callback C<cb> will be called if there is an out of memory
227 situation. I<Note this callback must not return>.
229 The default is to call L<abort(3)>.
231 You cannot set C<cb> to C<NULL>. You can't ignore out of memory
234 =head2 guestfs_get_out_of_memory_handler
236 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
238 This returns the current out of memory handler.
240 =head1 VERBOSE MESSAGES
242 =head2 guestfs_set_verbose
244 void guestfs_set_verbose (guestfs_h *handle, int verbose);
246 If C<verbose> is true, this turns on verbose messages (to C<stderr>).
248 Verbose messages are disabled unless the environment variable
249 C<LIBGUESTFS_DEBUG> is defined and set to C<1>.
251 =head2 guestfs_get_verbose
253 int guestfs_get_verbose (guestfs_h *handle);
255 This returns the verbose messages flag.
257 =head1 HIGH-LEVEL API ACTIONS
261 =head1 STATE MACHINE AND LOW-LEVEL EVENT API
263 Internally, libguestfs is implemented by running a virtual machine
264 using L<qemu(1)>. QEmu runs as a child process of the main program,
265 and most of this discussion won't make sense unless you understand
266 that the complexity is dealing with the (asynchronous) actions of the
270 ___________________ _________________________
272 | main program | | qemu +-----------------+|
273 | | | | Linux kernel ||
274 +-------------------+ | +-----------------+|
275 | libguestfs <-------------->| guestfsd ||
276 | | | +-----------------+|
277 \___________________/ \_________________________/
279 The diagram above shows libguestfs communicating with the guestfsd
280 daemon running inside the qemu child process. There are several
281 points of failure here: qemu can fail to start, the virtual machine
282 inside qemu can fail to boot, guestfsd can fail to start or not
283 establish communication, any component can start successfully but fail
284 asynchronously later, and so on.
288 libguestfs uses a state machine to model the child process:
299 / | \ \ guestfs_launch
305 / | guestfs_wait_ready
310 \______/ <------ \________/
312 The normal transitions are (1) CONFIG (when the handle is created, but
313 there is no child process), (2) LAUNCHING (when the child process is
314 booting up), (3) alternating between READY and BUSY as commands are
315 issued to, and carried out by, the child process.
317 The guest may be killed by C<guestfs_kill_subprocess>, or may die
318 asynchronously at any time (eg. due to some internal error), and that
319 causes the state to transition back to CONFIG.
321 Configuration commands for qemu such as C<guestfs_add_drive> can only
322 be issued when in the CONFIG state.
324 The high-level API offers two calls that go from CONFIG through
325 LAUNCHING to READY. C<guestfs_launch> is a non-blocking call that
326 starts up the child process, immediately moving from CONFIG to
327 LAUNCHING. C<guestfs_wait_ready> blocks until the child process is
328 READY to accept commands (or until some failure or timeout). The
329 low-level event API described below provides a non-blocking way to
330 replace C<guestfs_wait_ready>.
332 High-level API actions such as C<guestfs_mount> can only be issued
333 when in the READY state. These high-level API calls block waiting for
334 the command to be carried out (ie. the state to transition to BUSY and
335 then back to READY). But using the low-level event API, you get
336 non-blocking versions. (But you can still only carry out one
337 operation per handle at a time - that is a limitation of the
338 communications protocol we use).
340 Finally, the child process sends asynchronous messages back to the
341 main program, such as kernel log messages. Mostly these are ignored
342 by the high-level API, but using the low-level event API you can
343 register to receive these messages.
345 =head2 SETTING CALLBACKS TO HANDLE EVENTS
347 The child process generates events in some situations. Current events
348 include: receiving a reply message after some action, receiving a log
349 message, the child process exits, &c.
351 Use the C<guestfs_set_*_callback> functions to set a callback for
352 different types of events.
354 Only I<one callback of each type> can be registered for each handle.
355 Calling C<guestfs_set_*_callback> again overwrites the previous
356 callback of that type. Cancel all callbacks of this type by calling
357 this function with C<cb> set to C<NULL>.
359 =head2 NON-BLOCKING ACTIONS
361 XXX NOT IMPLEMENTED YET XXX
363 C<guestfs_set_reply_callback> is the most interesting callback to
364 play with, since it allows you to perform actions without blocking.
371 guestfs_main_loop_run (); /* --> blocks, then calls my_cb */
376 guestfs_set_reply_callback (handle, my_cb, data);
377 guestfs_nb_[action] (handle, [other parameters ...]);
378 /* returns immediately */
381 my_cb (guestfs_h *handle, void *data, XDR *xdr)
383 retval = guestfs_nb_[action]_r (handle, xdr);
387 There are C<guestfs_nb_*> and C<guestfs_nb_*_r> functions
388 corresponding to every C<guestfs_*> action in the high-level API.
390 =head2 guestfs_set_reply_callback
392 typedef void (*guestfs_reply_cb) (guestfs_h *g, void *opaque, XDR *xdr);
393 void guestfs_set_reply_callback (guestfs_h *handle,
397 The callback function C<cb> will be called whenever a reply is
398 received from the child process. (This corresponds to a transition
399 from the BUSY state to the READY state).
401 Note that the C<xdr> that you get in the callback is in C<XDR_DECODE>
402 mode, and you need to consume it before you return from the callback
403 function (since it gets destroyed after).
405 =head2 guestfs_set_log_message_callback
407 typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
409 void guestfs_set_log_message_callback (guestfs_h *handle,
410 guestfs_log_message_cb cb,
413 The callback function C<cb> will be called whenever qemu or the guest
414 writes anything to the console.
416 Use this function to capture kernel messages and similar.
418 Normally there is no log message handler, and log messages are just
421 =head2 guestfs_set_subprocess_quit_callback
423 typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
424 void guestfs_set_subprocess_quit_callback (guestfs_h *handle,
425 guestfs_subprocess_quit_cb cb,
428 The callback function C<cb> will be called when the child process
429 quits, either asynchronously or if killed by
430 C<guestfs_kill_subprocess>. (This corresponds to a transition from
431 any state to the CONFIG state).
433 =head2 guestfs_set_launch_done_callback
435 typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
436 void guestfs_set_launch_done_callback (guestfs_h *handle,
440 The callback function C<cb> will be called when the child process
441 becomes ready first time after it has been launched. (This
442 corresponds to a transition from LAUNCHING to the READY state).
444 You can use this instead of C<guestfs_wait_ready> to implement a
445 non-blocking wait for the child process to finish booting up.
447 =head2 EVENT MAIN LOOP
449 To use the low-level event API, you have to provide an event "main
450 loop". You can write your own, but if you don't want to write one,
451 two are provided for you:
455 =item libguestfs-select
457 A simple main loop that is implemented using L<select(2)>.
459 This is the default main loop unless you call C<guestfs_set_main_loop>
460 or C<guestfs_glib_set_main_loop>.
462 =item libguestfs-glib
464 An implementation which can be used with GLib and GTK+ programs. You
465 can use this to write graphical (GTK+) programs which use libguestfs
466 without hanging during long or slow operations.
470 =head2 guestfs_set_main_loop
472 void guestfs_set_main_loop (guestfs_main_loop *);
474 This call sets the current main loop to the list of callbacks
475 contained in the C<guestfs_main_loop> structure.
477 Only one main loop implementation can be used by libguestfs, so
478 calling this replaces the previous one. (So this is something that
479 has to be done by the main program, but only the main program "knows"
480 that it is a GTK+ program or whatever).
482 You should call this early in the main program, certainly before
483 calling C<guestfs_create>.
485 =head2 guestfs_glib_set_main_loop
487 void guestfs_glib_set_main_loop (GMainLoop *);
489 This helper calls C<guestfs_set_main_loop> with the correct callbacks
490 for integrating with the GLib main loop.
492 The libguestfs-glib main loop is contained in a separate library, so
493 that libguestfs doesn't depend on the whole of GLib:
496 #include <guestfs-glib.h>
501 g_main_loop_new (g_main_context_default (), 1);
503 guestfs_glib_set_main_loop (loop);
505 g_main_loop_run (loop);
508 To use this main loop you must link with C<-lguestfs-glib>. (See also
509 the GLib and GTK+ documentation).
511 =head2 guestfs_main_loop_run
513 void guestfs_main_loop_run (void);
515 This calls the main loop.
517 For some types of main loop you may want or prefer to call another
518 function, eg. C<g_main_loop_run>, or the main loop may already be
519 invoked by another part of your program. In those cases, ignore this
522 =head2 guestfs_main_loop_quit
524 void guestfs_main_loop_quit (void);
526 This instructs the main loop to quit. In other words,
527 C<guestfs_main_loop_run> will return.
529 For some types of main loop you may want or prefer to call another
530 function, eg. C<g_main_loop_quit>. In those cases, ignore this call.
532 =head2 WRITING A CUSTOM MAIN LOOP
534 This isn't documented. Please see the libguestfs-select and
535 libguestfs-glib implementations.
547 Richard W.M. Jones (C<rjones at redhat dot com>)
551 Copyright (C) 2009 Red Hat Inc.
552 L<http://et.redhat.com/~rjones/libguestfs>
554 This library is free software; you can redistribute it and/or
555 modify it under the terms of the GNU Lesser General Public
556 License as published by the Free Software Foundation; either
557 version 2 of the License, or (at your option) any later version.
559 This library is distributed in the hope that it will be useful,
560 but WITHOUT ANY WARRANTY; without even the implied warranty of
561 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
562 Lesser General Public License for more details.
564 You should have received a copy of the GNU Lesser General Public
565 License along with this library; if not, write to the Free Software
566 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA