libguestfs uses aug_get to get /files/etc/fstab/X/opt instead /files/etc/fstab/X/opt[Y]

[Zhongfu Li]

When running virt-sysprep on a VM file containing an fstab, with entries with multiple options, it will fail with "guestfsd: error: aug_get: /files/etc/fstab/1/opt: Too many matches for path expression: There are 2 nodes matching /files/etc/fstab/1/opt", or a similar error.

Augeas' aug_get only returns the value for a single node, and will fail with an error if there are multiple matches for the string. In this case, the nodes "/files/etc/fstab/1/opt[1]" and "/files/etc/fstab/1/opt[2]" exists and aug_get /files/etc/fstab/1/opt will match both of these nodes.

It appears that libguestfs does "aug_match /files/etc/fstab/1/opt" to get the nodes for all the options for the first entry (and so on), but it then runs "aug_get /files/etc/fstab/1/opt", which returns an error. I suspect that it's supposed to get the first option instead (/files/etc/fstab/1/opt[1]).

Ubuntu version: Ubuntu 16.04 LTS
libguestfs0 version: 1:1.32.2-4ubuntu2
libguestfs-tools version: 1:1.32.2-4ubuntu2

Additional information:
The image file in question is a qcow2 image file, with Ubuntu 16.04 "xenial" installed.
The partitions present on the qcow2 image are a FAT32 EFI System Partition, and a btrfs root filesystem with two subvolumes: @ (for /), and @home (for /home).
The fstab present on the installation of Ubuntu contains multiple fstab entries with multiple options, e.g. "relatime,subvol=@" for /

[Zhongfu Li (zhongfu)]

Bug still exists as of commit c711b517094375d4c321af4800e747b955643133 (https://github.com/libguestfs/libguestfs/commit/c711b517094375d4c321af4800e747b955643133)

[Richard Jones (rjones-redhat)]

Reproducer for this is:

$ virt-builder fedora-24

$ rm fedora-24-copy
$ truncate -s20G fedora-24-copy
$ virt-resize fedora-24.img fedora-24-copy

$ guestfish -a fedora-24-copy -i
><fs> list-filesystems
/dev/sda1: ext4
/dev/sda2: swap
/dev/sda3: xfs
/dev/sda4: unknown
><fs> mkfs btrfs /dev/sda4
><fs> list-filesystems
/dev/sda1: ext4
/dev/sda2: swap
/dev/sda3: xfs
/dev/sda4: btrfs
><fs> emacs /etc/fstab

... Add an extra fstab entry at the end of the file:

/dev/sda4 /home btrfs rw,user 0 0

... It doesn't matter what the options field says as long as there are
at least 2 options.

><fs> exit

$ virt-inspector fedora-24-copy
libguestfs: error: aug_get: aug_get: /files/etc/fstab/4/opt: Too many matches for path expression: There are 2 nodes matching /files/etc/fstab/4/opt

[Richard Jones (rjones-redhat)]

Patch posted:
https://www.redhat.com/archives/libguestfs/2016-August/msg00133.html

[Richard Jones (rjones-redhat)]

Fixed upstream in
https://github.com/libguestfs/libguestfs/commit/738c3bf4fdce569858369b2d2ce3879bf4b75f50
which will appear in libguestfs >= 1.35.2 and >= 1.34.1.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Landon Gilbert-Bland (landogbland)]

Any idea if the patched version will make it 16.04?

[Thomas Dreibholz (dreibh)]

The bug still exists in Ubuntu 16.04., more than one year after a fix has been released. Is there any backport available?

[Richard Jones (rjones-redhat)]

Someone's going to need to step up and become a maintainer, because there is currently no libguestfs maintainer for Ubuntu.

[Arnab Banerjee (arnabcse28)]

Looks like there's no fix available for Ubuntu 16.04 yet for this issue...