Clone of bug 1661038, so copying its important bits:

=========================================

Description of problem:

guestfish fails to correctly parse (some?) partitionless devices listed in /etc/fstab within a Linux image and unexpectedly exits with an error.

---

Version-Release number of selected component (if applicable):

$ guestfish --version
guestfish 1.38.2rhel=7,release=12.el7_6.1,libvirt

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How reproducible:

Consistently.

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Steps to Reproduce:

1. Build a qcow2 image for a Linux OS where '/etc/fstab' specifies where a device such as '/dev/vdc' should be mounted.

2. Run 'virt-inspector' on the image. Or run 'guestfish -a <image>', and from within the 'guestfish' shell, run 'launch' followed by 'inspect_os'.

As of this writing, the following are bootable images for Fedora 24 and Ubuntu 12.04 that illustrate the issue:

* https://platform.swampinabox.org/platform-images/condor-fedora-24-64-master-2016080801.qcow2.gz
* https://platform.swampinabox.org/platform-images/condor-ubuntu-12.04-64-master-2016102702.qcow2.gz

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Actual results:

$ virt-inspector condor-fedora-24-64-master-2016080801.qcow2 
libguestfs: error: inspect_os: int_of_string
virt-inspector: no operating system could be detected inside this disk image.

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Expected results:

Valid information.

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Additional info:

In the 'libguestfs' sources, 'daemon/inspect_fs_unix_fstab.ml' appears to contain a bug. The definition of 're_xdev' allows for partionless devices. The use of this regular expression within the function 'resolve_fstab_device' assumes that the string being matched does specify a partition:

    else if PCRE.matches re_xdev spec then (
      ...
      and part = int_of_string (PCRE.sub 3)
      ...
    )

See the attachment 'virt-inspector-verbose.txt' for the output from 'virt-inspector -v'. The following section appears to be relevant:

    check_fstab_entry: augeas path: /files/etc/fstab/5
    check_fstab_entry: spec=/dev/vdc
    check_fstab_entry: mp=/mnt/out
    resolve_fstab_device: /dev/vdc matched xdev
    ocaml_exn: 'inspect_os' raised 'Failure' exception
    guestfsd: error: int_of_string
    guestfsd: => inspect_os (0x1e0) took 1.14 secs
    libguestfs: error: inspect_os: int_of_string

=========================================

To be more precise: the OCaml code above assumes that the partition number is not an empty string, while re_xdev is:
  let re_xdev = PCRE.compile "^/dev/(h|s|v|xv)d([a-z]+)(\\d*)$"
which indeed can result in an empty string for the 3rd match.

This is a regression in the new OCaml code, compared to the old C one (in libguestfs < 1.38).
The old code just took the result of the 3rd match as string, using it as-is without trying to convert it as integer.

Sent a simple patch to fix this:
https://www.redhat.com/archives/libguestfs/2019-January/msg00103.html

=========================================

Fixed upstream with
https://github.com/libguestfs/libguestfs/commit/cf6b527824b2a8dc6e8bc65e38ebdceb227e6db1
which is in libguestfs >= 1.39.15.

This bug is fixed by the rebase scheduled for RHEL 7.7, see bug 1621895.

Verified with package:
libguestfs-1.40.2-1.el7.x86_64


Steps:

1. Download the condor-fedora-24-64-master-2016080801.qcow2 image from the link:
https://platform.swampinabox.org/platform-images/condor-fedora-24-64-master-2016080801.qcow2.gz
2. 
# virt-inspector -a condor-fedora-24-64-master-2016080801.qcow2
libguestfs: error: mount_ro: mount_ro_stub: /dev/vdb: expecting a device name
libguestfs: error: mount_ro: mount_ro_stub: /dev/vdc: expecting a device name
virt-inspector: some filesystems could not be mounted (ignored)
<?xml version="1.0"?>
<operatingsystems>
  <operatingsystem>
    <root>/dev/vg0/lv_root</root>
    <name>linux</name>
    <arch>x86_64</arch>
    <distro>fedora</distro>
    <product_name>Fedora 24 (Twenty Four)</product_name>
    <major_version>24</major_version>
    <minor_version>0</minor_version>
    <package_format>rpm</package_format>
    <package_management>dnf</package_management>
    <hostname>localhost.localdomain</hostname>
    <osinfo>fedora24</osinfo>
    <mountpoints>
      <mountpoint dev="/dev/vg0/lv_root">/</mountpoint>
      <mountpoint dev="/dev/sda2">/boot</mountpoint>
      <mountpoint dev="/dev/sdb">/mnt/in</mountpoint>
      <mountpoint dev="/dev/sdc">/mnt/out</mountpoint>
    </mountpoints>
    <filesystems>
      <filesystem dev="/dev/sda2">
        <type>ext4</type>
        <uuid>4c029e08-3e60-4227-8a5b-de2c500daf08</uuid>
      </filesystem>
      <filesystem dev="/dev/sdb"/>
      <filesystem dev="/dev/sdc"/>
      <filesystem dev="/dev/vg0/lv_root">
        <type>ext4</type>
        <uuid>36ef4986-e9a4-4177-b251-455618165972</uuid>
      </filesystem>
      <filesystem dev="/dev/vg0/lv_swap">
        <type>swap</type>
        <uuid>299e4b2f-4946-4b48-97ce-6b6afd4735e7</uuid>
      </filesystem>
    </filesystems>
...

The virt-inspector command can inspect the linux image when /etc/fstab contains a partionless device. Verified this bug.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2019:2096