=head1 SYNOPSIS
- guestfs_h handle = guestfs_create ();
+ #include <guestfs.h>
+
+ 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_file (handle, "/hello");
+ guestfs_touch (handle, "/hello");
guestfs_sync (handle);
guestfs_close (handle);
Libguestfs provides ways to enumerate guest storage (eg. partitions,
LVs, what filesystem is in each LV, etc.). It can also run commands
-in the context of the guest. Also you can mount guest filesystems on
-the host (requires root privs and NFS).
+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.
-=head1 CONNECTION MANAGEMENT
+You don't need to be root to use libguestfs, although obviously you do
+need enough permissions to access the disk images.
+
+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
+
+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 ();
+
+ /* 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);
+
+ /* 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 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.
+ */
+ guestfs_sync (handle);
+
+ /* Close the handle. */
+ guestfs_close (handle);
+
+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.
+
+=head2 DISK IMAGES
+
+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.
+
+You can add a disk read-only using C<guestfs_add_drive_ro>, in which
+case libguestfs won't modify the file.
+
+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.
+
+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.
+
+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.
+
+=head2 MOUNTING
+
+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:
+
+ guestfs_mount (handle, "/dev/sda1", "/");
+
+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>).
+
+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)>.
+
+To mount a disk image read-only, use C<guestfs_mount_ro>. There are
+several other variations of the C<guestfs_mount_*> call.
+
+=head2 FILESYSTEM ACCESS AND MODIFICATION
+
+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
+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.
+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.
+=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>
+For documentation see the file C<guestfs.mli>.
-=head1 CONFIGURATION MANAGEMENT
+=item B<Perl>
+For documentation see L<Sys::Guestfs(3)>.
+=item B<Python>
+For documentation do:
+ $ python
+ >>> import guestfs
+ >>> help (guestfs)
+
+=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
+=head2 guestfs_h *
-=head1 HIGH-LEVEL API
+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.
+For information on using multiple handles and threads, see the section
+L</MULTIPLE HANDLES AND MULTIPLE THREADS> below.
+=head2 guestfs_create
+ guestfs_h *guestfs_create (void);
+Create a connection handle.
+You have to call C<guestfs_add_drive> on the handle at least once.
+This function returns a non-NULL pointer to a handle on success or
+NULL on error.
+After configuring the handle, you have to call C<guestfs_launch>.
+You may also want to configure error handling for the handle. See
+L</ERROR HANDLING> section below.
+
+=head2 guestfs_close
+
+ void guestfs_close (guestfs_h *handle);
+
+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_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,
+ void *data,
+ const char *msg);
+ void guestfs_set_error_handler (guestfs_h *handle,
+ guestfs_error_handler_cb cb,
+ void *data);
+
+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.
+
+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.
+=head2 guestfs_get_error_handler
+ guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *handle,
+ void **data_rtn);
+Returns the current error handler callback.
+
+=head2 guestfs_set_out_of_memory_handler
+
+ typedef void (*guestfs_abort_cb) (void);
+ int guestfs_set_out_of_memory_handler (guestfs_h *handle,
+ guestfs_abort_cb);
+
+The callback C<cb> will be called if there is an out of memory
+situation. I<Note this callback must not return>.
+
+The default is to call L<abort(3)>.
+
+You cannot set C<cb> to C<NULL>. You can't ignore out of memory
+situations.
+
+=head2 guestfs_get_out_of_memory_handler
+
+ guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *handle);
+
+This returns the current out of memory handler.
+
+=head1 PATH
+
+Libguestfs needs a kernel and initrd.img, which it finds by looking
+along an internal path.
+
+By default it looks for these in the directory C<$libdir/guestfs>
+(eg. C</usr/local/lib/guestfs> or C</usr/lib64/guestfs>).
+
+Use C<guestfs_set_path> or set the environment variable
+C<LIBGUESTFS_PATH> to change the directories that libguestfs will
+search in. The value is a colon-separated list of paths. The current
+directory is I<not> searched unless the path contains an empty element
+or C<.>. For example C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would
+search the current directory and then C</usr/lib/guestfs>.
+
+=head1 HIGH-LEVEL API ACTIONS
+
+=head2 ABI GUARANTEE
+
+We guarantee the libguestfs ABI (binary interface), for public,
+high-level actions as outlined in this section. Although we will
+deprecate some actions, for example if they get replaced by newer
+calls, we will keep the old actions forever. This allows you the
+developer to program in confidence against libguestfs.
+
+@ACTIONS@
+
+=head1 STRUCTURES
+
+@STRUCTS@
=head1 STATE MACHINE AND LOW-LEVEL EVENT API
that the complexity is dealing with the (asynchronous) actions of the
child process.
+ child process
+ ___________________ _________________________
+ / \ / \
+ | main program | | qemu +-----------------+|
+ | | | | Linux kernel ||
+ +-------------------+ | +-----------------+|
+ | libguestfs <-------------->| guestfsd ||
+ | | | +-----------------+|
+ \___________________/ \_________________________/
+
+The diagram above shows libguestfs communicating with the guestfsd
+daemon running inside the qemu child process. There are several
+points of failure here: qemu can fail to start, the virtual machine
+inside qemu can fail to boot, guestfsd can fail to start or not
+establish communication, any component can start successfully but fail
+asynchronously later, and so on.
+
=head2 STATE MACHINE
libguestfs uses a state machine to model the child process:
/ | | 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
-
-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)
- {
- retval = guestfs_nb_[action]_r (handle);
- /* ... */
- }
-
-There are C<guestfs_nb_*> and C<guestfs_nb_*_r> functions
-corresponding to (very nearly) every C<guestfs_*> action in the
-high-level API.
-
-=head2 guestfs_set_reply_callback
-
- void guestfs_set_reply_callback (guestfs_handle h,
- 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 (I<important!>) that high-level API calls overwrite this
-callback.
-
=head2 guestfs_set_log_message_callback
- void guestfs_set_log_message_callback (guestfs_handle h,
+ typedef void (*guestfs_log_message_cb) (guestfs_h *g, void *opaque,
+ char *buf, int len);
+ void guestfs_set_log_message_callback (guestfs_h *handle,
guestfs_log_message_cb cb,
void *opaque);
=head2 guestfs_set_subprocess_quit_callback
- void guestfs_set_subprocess_quit_callback (guestfs_handle h,
+ typedef void (*guestfs_subprocess_quit_cb) (guestfs_h *g, void *opaque);
+ void guestfs_set_subprocess_quit_callback (guestfs_h *handle,
guestfs_subprocess_quit_cb cb,
void *opaque);
C<guestfs_kill_subprocess>. (This corresponds to a transition from
any state to the CONFIG state).
-=head2 guestfs_set_ready_callback
+=head2 guestfs_set_launch_done_callback
- void guestfs_set_ready_callback (guestfs_handle h,
- guestfs_ready_cb cb,
- void *opaque);
+ typedef void (*guestfs_launch_done_cb) (guestfs_h *g, void *opaque);
+ void guestfs_set_launch_done_callback (guestfs_h *handle,
+ guestfs_ready_cb cb,
+ void *opaque);
The callback function C<cb> will be called when the child process
-becomes ready. (This corresponds to a transition from I<either>
-LAUNCHING I<or> BUSY to the READY state).
+becomes ready first time after it has been launched. (This
+corresponds to a transition from LAUNCHING to the READY state).
+
+=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 *
+
+Is the string a parameter which is a device or partition name?
+
+=item *
+
+Does the string begin with C</dev/sd>?
+
+=item *
-You can use this instead of C<guestfs_wait_ready> to implement a
-non-blocking wait for the child process to finish booting up.
+Does the named device exist? If so, we use that device.
+However if I<not> then we continue with this algorithm.
-=head2 EVENT MAIN LOOP
+=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
-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:
+=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-poll
+=item *
-A simple main loop that is implemented using L<poll(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
-To use this main loop you must link with C<-lguestfs-glib>. (See also
-the GLib and GTK+ documentation).
+Pass additional options to the guest kernel.
-=head2 guestfs_main_loop_run
+=item LIBGUESTFS_DEBUG
- void guestfs_main_loop_run (void);
+Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
+has the same effect as calling C<guestfs_set_verbose (handle, 1)>.
-This calls the main loop.
+=item LIBGUESTFS_MEMSIZE
-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.
+Set the memory allocated to the qemu process, in megabytes. For
+example:
-=head2 guestfs_main_loop_quit
+ LIBGUESTFS_MEMSIZE=700
- void guestfs_main_loop_quit (void);
+=item LIBGUESTFS_PATH
-This instructs the main loop to quit. In other words,
-C<guestfs_main_loop_run> will return.
+Set the path that libguestfs uses to search for kernel and initrd.img.
+See the discussion of paths in section PATH above.
-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.
+=item LIBGUESTFS_QEMU
-=head2 WRITING A CUSTOM MAIN LOOP
+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.
-This isn't documented. Please see the libguestfs-poll and libguestfs-glib
-implementations.
+See also L</QEMU WRAPPERS> above.
+
+=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