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TODO list for libguestfs
This list contains random ideas and musings on features we could add
to libguestfs in future.
The API needs more test coverage, particularly lesser-used system
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).
Haskell bindings
Complete the Haskell bindings (see discussion on haskell-cafe).
PHP bindings
Add bindtests to PHP bindings.
Complete bind tests
Complete the bind tests - must test the return values and error cases.
virt-inspector - make libvirt XML
It should be possible to generate libvirt XML from virt-inspector
data, at least partially. This would be just another output type so:
virt-inspector --libvirt guest.img
Note that recent versions of libvirt/virt-install allow guests to be
imported, so this is not so useful any more.
"Standalone/local mode"
Instead of running guestfsd (the daemon) inside qemu, there should be
an option to just run guestfsd directly.
The architecture in this mode would look like:
| main program |
| libguestfs |
| | reply
cmd | |
| guestfsd |
(1) This only makes sense if we are running as root.
(2) There is no console / kernel messages in this configuration, but
we might consider capturing stderr from the daemon.
(3) guestfs_config and guestfs_add_drive become no-ops.
Obviously in this configuration, commands are run directly on the
local machine's disks. You could just run the commands themselves
directly, but libguestfs provides a convenient API and language
bindings. Also deals with tricky stuff like parsing the output of the
LVM commands. Also we get to leverage other code such as
This is mainly useful from live CDs, ie. virt-p2v.
Should we bother having the daemon at all and just link the guestfsd
code directly into libguestfs?
Ideas for extra commands
General glibc / core programs:
more mk*temp calls
ext2 properties:
fts(3) / ftw(3)
Other initrd-* commands
Such as:
Simple editing of configuration files
Some easy non-Augeas methods to edit configuration files.
I'm thinking:
replace /etc/file key value
which would look in /etc/file for any instances of
key ...
and replace them with
key value
That would solve about 50% of reconfiguration needs, and for the
rest you'd use Augeas, 'download'+'upload' or 'edit'.
RWMJ: I had a go at implementing this, but it's quite error-prone to
do this sort of editing inside the C-based daemon code. It's far
better to do it with Augeas, or else to use an external language like
Quick Perl scripts
Currently we can't do Perl "one-liners". ie. The current syntax for
any short Perl one-liner would be:
perl -MSys::Guestfs -e '$g = Sys::Guestfs->new(); $g->add_drive ("foo"); $g->launch; $g->mount ("/dev/sda1", "/"); ....'
You can see we're well beyond a single line just getting to the point
of adding drives and mounting.
First suggestion:
$h = create ($filename, \"/dev/sda1\" => \"/\");
$h = create ([$file1, $file2], \"/dev/sda1\" => \"/\");
To mount read-only, add C<ro =E<gt> 1> like this:
$h = create ($filename, \"/dev/sda1\" => \"/\", ro => 1);
which is equivalent to the following sequence of calls:
$h = Sys::Guestfs->new ();
$h->add_drive_ro ($filename);
$h->launch ();
$h->mount_ro (\"/dev/sda1\", \"/\");
Command-line form would be:
perl -MSys::Guestfs=:all -e '$_=create("guest.img", "/dev/sda1" => "/"); $_->cat ("/etc/fstab");'
That's not brief enough for one-liners, so we could have an extra
autogenerated module which creates a Sys::Guestfs handle singleton
(the handle is an implicit global variable as in guestfish), eg:
perl -MSys::Guestfs::One -e 'inspect("guest.img"); cat ("/etc/fstab");'
How would editing files work?
virt-rescue pty
Note that pty requires cooperation inside the C code too (there are
two sides to a pty, and one has to be handled after the fork).
[I tried to implement this in the new C virt-rescue, but it doesn't
work. qemu is implementing its own ptys, and they are broken. Need
to fix qemu.]
Windows-based daemon/appliance
See discussion on list:
qemu locking
Add -drive file=...,lock=exclusive and -drive file=...,lock=shared
Change libguestfs and libvirt to do the right thing, so that multiple
instances of qemu cannot stomp on each other.
For multi-level disk images such as live CDs:
It's possible with libguestfs to recursively look for anything that
might be a filesystem, mount-{,loop} it and look in those, revealing
anything in a disk image.
However this won't work easily for VM disk images in the disk image.
One would have to download those to the host and launch another
libguestfs instance.
[Not sure this is such a good idea. See also live CD inspection idea below.]
Map filesystems to disk blocks
Map files/filesystems/(any other object) to the actual disk
blocks they occupy.
And vice versa.
Is it even possible?
See also contribs/visualize-alignment/
Integration with host intrusion systems
Perfect way to monitor VMs from outside the VM. Look for file
hashes, log events, login/logout etc.
Fix 'file'
Freeze/thaw filesystems
Access to these ioctls:
Tips for new users in guestfish
$ guestfish
Tip: You need to 'add disk.img' or 'alloc disk.img nn' to make a new image.
Type 'notips' to disable tips permanently.
><fs> add mydisk
Tip: You need to type 'run' before you can see into the disk image.
><fs> run
Tip: Use 'list-filesystems' to see what filesystems are available.
><fs> list-filesystems
Tip: Use 'mount fs /' to mount a filesystem.
><fs> mount /dev/vda1 /
Tip: Use 'll /' to view the filesystem or ...
><fs> ll /
Could we make guestfish interactive if commands are used without params?
><fs> sparse
[[Prints man page]]
Image name? disk.img
Size of image? 10M
Common problems
How can we solve these common user problems?
[space for common problems here]
Better support for encrypted devices
Currently LUKS support only works if the device contains volume
groups. If it contains, eg., partitions, you cannot access them.
We would like to add:
- Direct access to the /dev/mapper device (eg. if it contains
anything apart from VGs).
Display image as PS
Display the structure of an image file as a PS.
Greater use of blkid / libblkid
guestfs_zero should use wipefs. See wipefs(8).
There are various useful functions in libblkid for listing partitions,
devices etc which we are essentially duplicating in the daemon. It
would make more sense to just use libblkid for this.
There are some places where we call out to the 'blkid' program. This
might be replaced by direct use of the library (if this is easier).
Eric Sandeen pointed out the blktrace tool which is a better way of
capturing traces than using patched qemu (see
contrib/visualize-alignment). We would still use the same
visualization tools in conjunction with blktrace traces.
guestfish parsing
At the moment guestfish uses an ad hoc parser which has many
shortcomings. We should change to using a lex/yacc-based scanner and
parser (there are better parsers out there, but yacc is sufficient and
very widely available).
The scanner must deal with the case of parsing a whole command string,
eg. for a command that the user types in:
><fs> add-drive-opts "/tmp/foo" readonly:true
and also with parsing single words from the command line:
guestfish add-drive-opts /tmp/foo readonly:true
Note the quotes are for scanning and don't indicate types.
We should also allow variables and expressions as part of this new
parsing code, eg:
set roots inspect-os
set product inspect-get-product-name %{roots[0]}
% is better than $ because of shell escaping and confusion with shell
Can we combine this with ability to set and read environment
variables? Currently guestfish uses many environment variables like
$EDITOR without any corresponding ability to set them.
set EDITOR /usr/bin/emacs
echo $EDITOR # or %{EDITOR}
edit /etc/resolv.conf
live CD inspection for Windows 7
Windows 7 install CDs are quite different and pretty impenetrable.
There are no obvious files to parse.
More ntfs tools
ntfsprogs actually has a lot more useful tools than we currently
use. Interesting ones are:
ntfslabel: display or change filesystem label (we should unify all
set*label APIs into a single set_vfs_label which can deal with any
ntfsclone: clone, image, restore, rescue NTFS
ntfsinfo: print various information about NTFS volume and files
ntfs streams: extract alternate streams from NTFS files
ntfsck: checker for NTFS filesystems
Undelete files
Two useful tools:
- ext2undelete
- ntfsundelete
More mkfs_opts options
Useful options to offer:
- Set label.
- Set UUID.
Use /proc/self/mountinfo
This file contains lots of interesting information about
what is mounted and where. eg:
16 21 0:3 / /proc rw,relatime - proc /proc rw
17 21 0:16 / /sys rw,relatime - sysfs /sys rw,seclabel
18 23 0:5 / /dev rw,relatime - devtmpfs udev rw,seclabel,size=1906740k,nr_inodes=476685,mode=755
26 21 253:3 / /home rw,relatime - ext4 /dev/mapper/vg-lv_home rw,seclabel,barrier=1,data=ordered
This could be used instead of current hairy code to parse the output
of the 'mount' command. We could add new APIs to return kernel mount
options, type of filesystem at a mountpoint etc.
guestfish drive letters
There should be an option to mount all Windows drives as separate
paths, like C: => /c/, D: => /d/ etc.
More inspection features
- last shutdown time
- DHCP address
- last time the software was updated
- last user who logged in
- lastlog, last, who
Integrate virt-inspector with CMDBs
Either integrate virt-inspector with Configuration Management
Databases (CMDBs) or at least check that virt-inspector produces the
right range of data so that integration would be possible. The
standards for CMDBs come from the DMTF, see eg:
Efficient way to visit all files
A naive method would look like:
g#visit ~return_stats:true "/" (
fun pathname stat ->
However this has two disadvantages:
- requires hand-written custom bindings in each language
- unclear about locking, thread-safety and re-entrancy of handle g
A better way would be to have some sort of explicit "download all
filenames and stat structures", which could then be iterated over:
let files = g#find_opts ~return_stats:true "/" in
List.iter (
fun pathname stat ->
The problem with this is that 'files' is going to be larger than a
protocol buffer.
This leads to thinking about changes to the protocol / generator to
make this simpler. The proposal would be to add RBigStringList,
RBigStructList [or RBig (Ranytype ...)]. These would work like
FileOut, in that they would use file streaming to stream XDR
structures (probably written to a file on the library side).
Generated code would hide most of the implementation.
We also need to think about security issues: is it possible for the
daemon to keep sending back data forever, and if so what happens on
the library side.
[Users can now use virt-ls to solve some of these problems, but it is
not a general solution at the API level]
Interactive disk creator
An interactive disk creator program.
Attach method for disconnected operation
"Librarian" has an idea that he should be able to attach to a regular
appliance, but disconnect from it and reconnect to it later. This
would be some sort of modified attach method (see link above).
The complexity here is that we would no longer have access to
stdin/stdout (or we'd have to direct that somewhere else).
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