=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
This isn't documented. Please see the libguestfs-select and
libguestfs-glib implementations.
+=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 *
+
+Does the named device exist? If so, we use that device.
+However if I<not> then we continue with this algorithm.
+
+=item *
+
+Replace initial C</dev/sd> string with C</dev/hd>.
+
+For example, change C</dev/sda2> to C</dev/hda2>.
+
+If that named device exists, use it. If not, continue.
+
+=item *
+
+Replace initial C</dev/sd> string with C</dev/vd>.
+
+If that named device exists, use it. If not, return an error.
+
+=back
+
+=head2 PORTABILITY CONCERNS
+
+Although the standard naming scheme and automatic translation is
+useful for simple programs and guestfish scripts, for larger programs
+it is best not to rely on this mechanism.
+
+Where possible for maximum future portability programs using
+libguestfs should use these future-proof techniques:
+
+=over 4
+
+=item *
+
+Use C<guestfs_list_devices> or C<guestfs_list_partitions> to list
+actual device names, and then use those names directly.
+
+Since those device names exist by definition, they will never be
+translated.
+
+=item *
+
+Use higher level ways to identify filesystems, such as LVM names,
+UUIDs and filesystem labels.
+
+=back
+
=head1 INTERNALS
=head2 COMMUNICATION PROTOCOL
LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
+Note that libguestfs also calls qemu with the -help and -version
+options in order to determine features.
+
=head1 ENVIRONMENT VARIABLES
=over 4
+=item LIBGUESTFS_APPEND
+
+Pass additional options to the guest kernel.
+
=item LIBGUESTFS_DEBUG
Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages. This
has the same effect as calling C<guestfs_set_verbose (handle, 1)>.
+=item LIBGUESTFS_MEMSIZE
+
+Set the memory allocated to the qemu process, in megabytes. For
+example:
+
+ LIBGUESTFS_MEMSIZE=700
+
=item LIBGUESTFS_PATH
Set the path that libguestfs uses to search for kernel and initrd.img.
See also L<QEMU WRAPPERS> above.
-=item LIBGUESTFS_APPEND
-
-Pass additional options to the guest kernel.
-
=back
=head1 SEE ALSO
L<guestfish(1)>,
L<qemu(1)>,
L<febootstrap(1)>,
-L<http://et.redhat.com/~rjones/libguestfs>.
+L<http://libguestfs.org/>.
+
+=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.
+
+=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