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
you have created through L<posix_fallocate(3)>. Libguestfs lets you
do useful things to all of these.
-You can add a disk read-only using L</guestfs_add_drive_ro>, in which
+The call you should use in modern code for adding drives is
+L</guestfs_add_drive_opts>. To add a disk image, allowing writes, and
+specifying that the format is raw, do:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
+ -1);
+
+You can add a disk read-only using:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
+ GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+ -1);
+
+or by calling the older function L</guestfs_add_drive_ro>. In either
case libguestfs won't modify the file.
Be extremely cautious if the disk image is in use, eg. if it is being
L</guestfs_list_partitions> and L</guestfs_lvs> to list possible
partitions and LVs, and either try mounting each to see what is
mountable, or else examine them with L</guestfs_vfs_type> or
-L</guestfs_file>. But you might find it easier to look at higher level
-programs built on top of libguestfs, in particular
-L<virt-inspector(1)>.
+L</guestfs_file>. 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 L</guestfs_mount_ro>. There are
several other variations of the C<guestfs_mount_*> call.
=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.
+
=back
The two main API calls to run commands are L</guestfs_command> and
For more information about umask, see L<umask(2)>.
+=head2 ENCRYPTED DISKS
+
+Libguestfs allows you to access Linux guests which have been
+encrypted using whole disk encryption that conforms to the
+Linux Unified Key Setup (LUKS) standard. This includes
+nearly all whole disk encryption systems used by modern
+Linux guests.
+
+Use L</guestfs_vfs_type> to identify LUKS-encrypted block
+devices (it returns the string C<crypto_LUKS>).
+
+Then open these devices by calling L</guestfs_luks_open>.
+Obviously you will require the passphrase!
+
+Opening a LUKS device creates a new device mapper device
+called C</dev/mapper/mapname> (where C<mapname> is the
+string you supply to L</guestfs_luks_open>).
+Reads and writes to this mapper device are decrypted from and
+encrypted to the underlying block device respectively.
+
+LVM volume groups on the device can be made visible by calling
+L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.
+The logical volume(s) can now be mounted in the usual way.
+
+Use the reverse process to close a LUKS device. Unmount
+any logical volumes on it, deactivate the volume groups
+by caling C<guestfs_vg_activate (g, 0, ["/dev/VG"])>.
+Then close the mapper device by calling
+L</guestfs_luks_close> on the C</dev/mapper/mapname>
+device (I<not> the underlying encrypted block device).
+
+=head2 INSPECTION
+
+Libguestfs has APIs for inspecting an unknown disk image to find out
+if it contains operating systems. (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.
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:
dirty guestfish scripts that forget to sync will work just fine, which
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 L</guestfs_mount>, then C<-o sync,noatime> are added
since. Like the Bourne shell, we should have used C<guestfish -c
command> to run commands.
-=item Protocol limit of 256 characters for error messages
+=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:
-This limit is both rather small and quite unnecessary. We should be
-able to return error messages up to the length of the protocol message
-(2-4 MB).
+ lvcreate LV VG 100M
-Note that we cannot change the protocol without some breakage, because
-there are distributions that repackage the Fedora appliance.
+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.
-=item Protocol should return errno with error messages.
+This could be fixed in the generator by specially marking parameters
+and return values which take bytes or other units.
-It would be a nice-to-have to be able to get the original value of
-'errno' from inside the appliance along error paths (where set).
-Currently L<guestmount(1)> goes through hoops to try to reverse the
-error message string into an errno, see the function error() in
-fuse/guestmount.c.
+=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
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.
+
=head1 CONNECTION MANAGEMENT
=head2 guestfs_h *
Create a connection handle.
-You have to call L</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.
=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 L</guestfs_last_error> and/or by setting up an error
-handler with L</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.
+
+For other programs the caller will almost certainly want to install an
+alternate error handler or do error handling in-line like this:
-The default error handler prints the information string to C<stderr>.
+ g = guestfs_create ();
+
+ /* This disables the default behaviour of printing errors
+ on stderr. */
+ guestfs_set_error_handler (g, NULL, NULL);
+
+ if (guestfs_launch (g) == -1) {
+ /* Examine the error message and print it etc. */
+ char *msg = guestfs_last_error (g);
+ int errnum = guestfs_last_errno (g);
+ fprintf (stderr, "%s\n", msg);
+ /* ... */
+ }
Out of memory errors are handled differently. The default action is
to call L<abort(3)>. If this is undesirable, then you can set a
handler using L</guestfs_set_out_of_memory_handler>.
+L</guestfs_create> returns C<NULL> if the handle cannot be created,
+and because there is no handle if this happens there is no way to get
+additional error information. However L</guestfs_create> is supposed
+to be a lightweight operation which can only fail because of
+insufficient memory (it returns NULL in this case).
+
=head2 guestfs_last_error
const char *guestfs_last_error (guestfs_h *g);
The lifetime of the returned string is until the next error occurs, or
L</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_last_errno
+
+ int guestfs_last_errno (guestfs_h *g);
+
+This returns the last error number (errno) that happened on C<g>.
+
+If successful, an errno integer not equal to zero is returned.
+
+If no error, this returns 0. This call can return 0 in three
+situations:
+
+=over 4
+
+=item 1.
+
+There has not been any error on the handle.
+
+=item 2.
+
+There has been an error but the errno was meaningless. This
+corresponds to the case where the error did not come from a
+failed system call, but for some other reason.
+
+=item 3.
+
+There was an error from a failed system call, but for some
+reason the errno was not captured and returned. This usually
+indicates a bug in libguestfs.
+
+=back
+
+Libguestfs tries to convert the errno from inside the applicance into
+a corresponding errno for the caller (not entirely trivial: the
+appliance might be running a completely different operating system
+from the library and error numbers are not standardized across
+Un*xen). If this could not be done, then the error is translated to
+C<EINVAL>. In practice this should only happen in very rare
+circumstances.
=head2 guestfs_set_error_handler
typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
- void *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.
=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
+=head1 CALLS WITH OPTIONAL ARGUMENTS
+
+A recent feature of the API is the introduction of calls which take
+optional arguments. In C these are declared 3 ways. The main way is
+as a call which takes variable arguments (ie. C<...>), as in this
+example:
+
+ int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);
+
+Call this with a list of optional arguments, terminated by C<-1>.
+So to call with no optional arguments specified:
+
+ guestfs_add_drive_opts (g, filename, -1);
+
+With a single optional argument:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ -1);
+
+With two:
+
+ guestfs_add_drive_opts (g, filename,
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
+ GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
+ -1);
+
+and so forth. Don't forget the terminating C<-1> otherwise
+Bad Things will happen!
+
+=head2 USING va_list FOR OPTIONAL ARGUMENTS
+
+The second variant has the same name with the suffix C<_va>, which
+works the same way but takes a C<va_list>. See the C manual for
+details. For the example function, this is declared:
+
+ int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
+ va_list args);
+
+=head2 CONSTRUCTING OPTIONAL ARGUMENTS
+
+The third variant is useful where you need to construct these
+calls. You pass in a structure where you fill in the optional
+fields. The structure has a bitmask as the first element which
+you must set to indicate which fields you have filled in. For
+our example function the structure and call are declared:
+
+ struct guestfs_add_drive_opts_argv {
+ uint64_t bitmask;
+ int readonly;
+ const char *format;
+ /* ... */
+ };
+ int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
+ const struct guestfs_add_drive_opts_argv *optargs);
+
+You could call it like this:
+
+ struct guestfs_add_drive_opts_argv optargs = {
+ .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
+ GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
+ .readonly = 1,
+ .format = "qcow2"
+ };
+
+ guestfs_add_drive_opts_argv (g, filename, &optargs);
+
+Notes:
+
+=over 4
+
+=item *
+
+The C<_BITMASK> suffix on each option name when specifying the
+bitmask.
+
+=item *
+
+You do not need to fill in all fields of the structure.
+
+=item *
+
+There must be a one-to-one correspondence between fields of the
+structure that are filled in, and bits set in the bitmask.
+
+=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>.
+
=begin html
<!-- old anchor for the next section -->
Configuration commands for qemu such as L</guestfs_add_drive> can only
be issued when in the CONFIG state.
-The high-level API offers two calls that go from CONFIG through
-LAUNCHING to READY. L</guestfs_launch> blocks until the child process
-is READY to accept commands (or until some failure or timeout).
+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.
-High-level API actions such as L</guestfs_mount> can only be issued
-when in the READY state. These high-level API calls block waiting for
-the command to be carried out (ie. the state to transition to BUSY and
-then back to READY). But using the low-level event API, you get
-non-blocking versions. (But you can still only carry out one
-operation per handle at a time - that is a limitation of the
-communications protocol we use).
+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. Mostly these are ignored
-by the high-level API, but using the low-level event API you can
-register to receive these messages.
+main program, such as kernel log messages. You can register a
+callback to receive these messages.
=head2 SETTING CALLBACKS TO HANDLE EVENTS
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).
+=head2 guestfs_set_close_callback
+
+ typedef void (*guestfs_close_cb) (guestfs_h *g, void *opaque);
+ void guestfs_set_close_callback (guestfs_h *g,
+ guestfs_close_cb cb,
+ void *opaque);
+
+The callback function C<cb> will be called while the handle
+is being closed (synchronously from L</guestfs_close>).
+
+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).
+
+=head2 guestfs_set_progress_callback
+
+ 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);
+
+Some long-running operations can generate progress messages. If
+this callback is registered, then it will be called each time a
+progress message is generated (usually two seconds after the
+operation started, and three times per second thereafter until
+it completes, although the frequency may change in future versions).
+
+The 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 only defined and stable parts of the API are:
+
+=over 4
+
+=item *
+
+The callback can display to the user some type of progress bar or
+indicator which shows the ratio of C<position>:C<total>.
+
+=item *
+
+0 E<lt>= C<position> E<lt>= C<total>
+
+=item *
+
+If any progress notification is sent during a call, then a final
+progress notification is always sent when C<position> = C<total>.
+
+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.
+
+=back
+
+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.
+
+=head1 PRIVATE DATA AREA
+
+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.
+
+To attach a named piece of data, use the following call:
+
+ void guestfs_set_private (guestfs_h *g, const char *key, void *data);
+
+C<key> is the name to associate with this data, and C<data> is an
+arbitrary pointer (which can be C<NULL>). Any previous item with the
+same name is overwritten.
+
+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.
+
+To retrieve the pointer, use:
+
+ void *guestfs_get_private (guestfs_h *g, const char *key);
+
+This function returns C<NULL> if either no data is found associated
+with C<key>, or if the user previously set the C<key>'s C<data>
+pointer to C<NULL>.
+
+Libguestfs does not try to look at or interpret the C<data> pointer in
+any way. As far as libguestfs is concerned, it need not be a valid
+pointer at all. In particular, libguestfs does I<not> try to free the
+data when the handle is closed. If the data must be freed, then the
+caller must either free it before calling L</guestfs_close> or must
+set up a close callback to do it (see L</guestfs_set_close_callback>,
+and note that only one callback can be registered for a handle).
+
+The private data area is implemented using a hash table, and should be
+reasonably efficient for moderate numbers of keys.
+
=head1 BLOCK DEVICE NAMING
In the kernel there is now quite a profusion of schemata for naming
=head3 INITIAL MESSAGE
-Because the underlying channel (QEmu -net channel) doesn't have any
-sort of connection control, when the daemon launches it sends an
-initial word (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest
-and daemon is alive. This is what L</guestfs_launch> waits for.
+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.
+
+=head3 PROGRESS NOTIFICATION MESSAGES
+
+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.
+
+The library turns them into progress callbacks (see
+C<guestfs_set_progress_callback>) if there is a callback registered,
+or discards them if not.
+
+The daemon self-limits the frequency of progress messages it sends
+(see C<daemon/proto.c:notify_progress>). Not all calls generate
+progress messages.
=head1 MULTIPLE HANDLES AND MULTIPLE THREADS
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.
+
=head1 QEMU WRAPPERS
If you want to compile your own qemu, run qemu from a non-standard
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.
git.annexia.org / libguestfs.git / blobdiff