FUSE filesystem support.

This implements FUSE filesystem support so that any libguestfs-
accessible disk image can be mounted as a local filesystem.

Note: file writes (ie. write(2) system call) is not yet implemented.

The API needs more test coverage, particularly lesser-used system
calls.

The big unresolved issue is UID/GID mapping between guest filesystem
IDs and the host.  It's not easy to automate this because you need
extra details about the guest itself in order to get to its
UID->username map (eg. /etc/passwd from the guest).

1 files changed, 205 insertions, 0 deletions

diff --git a/fuse/guestmount.pod b/fuse/guestmount.pod
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+=encoding utf8
+
+=head1 NAME
+
+guestmount - Mount a guest filesystem on the host using FUSE and libguestfs
+
+=head1 SYNOPSIS
+
+ guestmount [--options] -a disk.img -m device [--ro] mountpoint
+
+=head1 WARNING
+
+You must I<not> use C<guestmount> in read-write mode on live virtual
+machines.  If you do this, you risk disk corruption in the VM.
+
+=head1 DESCRIPTION
+
+The guestmount program can be used to mount virtual machine
+filesystems and other disk images on the host.  It uses libguestfs for
+access to the guest filesystem, and FUSE (the "filesystem in
+userspace") to make it appear as a mountable device.
+
+Along with other options, you have to give at least one device (I<-a>
+option) and at least one mountpoint (I<-m> option).  How this works is
+better explained in the L<guestfish(1)> manual page, or you can use
+L<virt-inspector(1)> and/or the the wrapper script
+C<guestmount-wrapper> to help you.
+
+FUSE lets you mount filesystems as non-root.  The mountpoint must be
+owned by you, and the filesystem will not be visible to any other
+users unless you make certain global configuration changes to
+C</etc/fuse.conf>.  To unmount the filesystem, use the C<fusermount -u>
+command.
+
+=head1 EXAMPLES
+
+For a typical Windows guest which has its main filesystem on the
+first partition:
+
+ guestmount -a windows.img -m /dev/sda1 --ro /mnt
+
+For a typical Linux guest which has a /boot filesystem on the first
+partition, and the root filesystem on a logical volume:
+
+ guestmount -a linux.img -m /dev/VG/LV -m /dev/sda1:/boot --ro /mnt
+
+To get L<virt-inspector(1)> to do the hard work of detecting guest
+mountpoints for you:
+
+ guestmount $(virt-inspector --ro-fish MyGuest) /mnt
+
+(or use --fish if you don't want it to be a read only mount).  The
+option is called I<--ro-fish> or I<--fish> because these parameters
+are compatible with L<guestfish(1)>.
+
+If you want to trace the libguestfs calls but without excessive
+debugging, we recommend:
+
+ guestmount [-a ... -m ...] --trace /mnt
+
+If you want to debug the program, we recommend:
+
+ guestmount [-a ... -m ...] --trace --verbose /mnt
+
+=head1 OPTIONS
+
+=over 4
+
+=item B<-a image> | B<--add image>
+
+Add a block device or virtual machine image.
+
+=item B<--dir-cache-timeout N>
+
+Set the readdir cache timeout to I<N> seconds, the default being 60
+seconds.  The readdir cache [actually, there are several
+semi-independent caches] is populated after a readdir(2) call with the
+stat and extended attributes of the files in the directory, in
+anticipation that they will be requested soon after.
+
+There is also a different attribute cache implemented by FUSE
+(see the FUSE option I<-o attr_timeout>), but the FUSE cache
+does not anticipate future requests, only cache existing ones.
+
+=item B<--fuse-help>
+
+Display help on special FUSE options (see I<-o> below).
+
+=item B<--help>
+
+Display brief help and exit.
+
+=item B<-m dev[:mnt]> | B<--mount dev[:mnt]>
+
+Mount the named partition or logical volume on the given mountpoint
+B<in the guest> (this has nothing to do with mountpoints in the host).
+
+If the mountpoint is omitted, it defaults to C</>.  You have to mount
+something on C</>.
+
+=item B<-n> | B<--no-sync>
+
+By default, we attempt to sync the guest disk when the FUSE mountpoint
+is unmounted.  If you specify this option, then we don't attempt to
+sync the disk.  See the discussion of autosync in the L<guestfs(3)>
+manpage.
+
+=item B<-o option> | B<--option option>
+
+Pass extra options to FUSE.
+
+To get a list of all the extra options supported by FUSE, use the
+command below.  Note that only the FUSE I<-o> options can be passed,
+and only some of them are a good idea.
+
+ guestmount --fuse-help
+
+Some potentially useful FUSE options:
+
+=over 4
+
+=item B<-o allow_other>
+
+Allow other users to see the filesystem.
+
+=item B<-o attr_timeout=N>
+
+Enable attribute caching by FUSE, and set the timeout to I<N> seconds.
+
+=item B<-o kernel_cache>
+
+Allow the kernel to cache files (reduces the number of reads
+that have to go through the L<guestfs(3)> API).  This is generally
+a good idea if you can afford the extra memory usage.
+
+=item B<-o uid=N> B<-o gid=N>
+
+Use these options to map all UIDs and GIDs inside the guest filesystem
+to the chosen values.
+
+=back
+
+=item B<-r> | B<--ro>
+
+Add devices and mount everything read-only.  Also disallow writes and
+make the disk appear read-only to FUSE.
+
+This is highly recommended if you are not going to edit the guest
+disk.  If the guest is running and this option is I<not> supplied,
+then there is a strong risk of disk corruption in the guest.  We try
+to prevent this from happening, but it is not always possible.
+
+=item B<--selinux>
+
+Enable SELinux support for the guest.
+
+=item B<--trace>
+
+Trace libguestfs calls (to stderr).
+
+This also stops the daemon from forking into the background.
+
+=item B<-v> | B<--verbose>
+
+Enable verbose messages from underlying libguestfs.
+
+=item B<-V> | B<--version>
+
+Display the program version and exit.
+
+=back
+
+=head1 SEE ALSO
+
+L<guestfish(1)>,
+L<virt-inspector(1)>,
+L<virt-cat(1)>,
+L<virt-edit(1)>,
+L<virt-tar(1)>,
+L<guestfs(3)>,
+L<http://libguestfs.org/>,
+L<http://fuse.sf.net/>.
+
+=head1 AUTHORS
+
+Richard W.M. Jones (C<rjones at redhat dot com>)
+
+=head1 COPYRIGHT
+
+Copyright (C) 2009 Red Hat Inc.
+L<http://libguestfs.org/>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.