Libguestfs - Dec 2021 - [v2v PATCH v2] convert_linux: translate the first CD-ROM's references in boot conf files

On 12/15/21 16:31, Laszlo Ersek wrote:
> If the only CD-ROM in "s_removables" is on an IDE controller, and
the
> guest kernel represents it with a /dev/hdX device node, then convert
> references to this device node, in the boot config files, to /dev/cdrom.
> On the destination (after conversion), /dev/cdrom will point to whataver
> node we converted the CD-ROM to, masking a potential i440fx -> q35 (IDE
->
> SATA) board change.
> 
> If the only CD-ROM is not on an IDE controller, or the guest is modern
> enough to represent the IDE CD-ROM as /dev/sr0, then perform no
> translation. Namely, /dev/sr0 survives a potential i440fx -> q35 (IDE
->
> SATA) board change intact.
> 
> When multiple CD-ROMs exist, emit a warning, and attempt the conversion on
> the first CD-ROM, as a guess. This may be inexact, but we can't do
better,
> because:
> 
> - SATA, SCSI, and (on modern guests) IDE CD-ROMs are lumped together in
>   the /dev/sr* namespace, on the source side, and
"s_removable_slot" is
>   useless for telling them apart, as we don't know the exact controller
>   topology (and OS enumeration order);
> 
> - after conversion: some OSes don't create /dev/cdrom* symlinks to all
>   CD-ROMs, and even if multiple such symlinks are created, their order is
>   basically random.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1637857
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> Notes:
>     v2:
>     
>     - Use List.length >= 2 rather than matching with three cons
operations.
>       [Rich]
>     
>     - At the same time, eliminate wrong precedence between
"->" in a match,
>       and ";". [Rich]
>     
>     - Match the first element of the cdrom list, and the contents of that
>       element, in a single "match" expression. [Rich]
>     
>     - Not tested, due to the issue I described in
>       <8b3ce08b-ea47-dc1c-f441-c8b91708bd6f at redhat.com> (cannot
provide a
>       mailing list URL because the archive seems to have stopped refreshing
>       itself?)
> 
>  convert/convert_linux.ml      | 19 +++++++++++++++++++
>  tests/test-v2v-cdrom.expected |  2 +-
>  tests/test-v2v-cdrom.xml.in   |  4 +++-
>  tests/test-v2v-i-ova.xml      |  2 +-
>  4 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/convert/convert_linux.ml b/convert/convert_linux.ml
> index 8dc648169dcb..d49ecec03aeb 100644
> --- a/convert/convert_linux.ml
> +++ b/convert/convert_linux.ml
> @@ -1020,6 +1020,25 @@ let convert (g : G.guestfs) source inspect
keep_serial_console _ >            "xvd" ^ drive_name i,
block_prefix_after_conversion ^ drive_name i
>        ) source.s_disks in
>  
> +    (* Check the first CD-ROM. If its controller is IDE, and the OS is
RHEL<=5,
> +     * then translate the CD-ROM from "/dev/hd[SLOT]" to
"/dev/cdrom". See
> +     * RHBZ#1637857 for details.
> +     *)
> +    let cdroms = List.filter
> +                   (fun removable -> removable.s_removable_type =
CDROM)
> +                   source.s_removables in
> +    if List.length cdroms >= 2 then
> +      warning (f_"multiple CD-ROMs found; translation of CD-ROM
references \
> +                  may be inexact");
> +    let map = map @
> +      (match cdroms with
> +       | { s_removable_controller = Some Source_IDE;
> +           s_removable_slot = Some slot } :: _
> +         when family = `RHEL_family && inspect.i_major_version
<= 5 ->
> +           [("hd" ^ drive_name slot, "cdrom")]
> +       | _ -> []
> +      ) in
> +
>      if verbose () then (
>        eprintf "block device map:\n";
>        List.iter (
After updating my workstation to F35 and rebuilding everything, this
patch seems to do the right thing in a synthetic test.

Namely, in the input guest, I added an entry to /etc/fstab, mounting
/dev/hda (an IDE CD-ROM) as /mnt2. After conversion with

virt-v2v  -i libvirt -o libvirt -on rhel5.11.out rhel5.11

I checked the output disk manually with guestfish, and /dev/hda had
indeed been replaced with /dev/cdrom in the same /etc/fstab entry.
Additionally, when passing "-v -x" to the above command line, the
debug
output contains:
> block device map:
>         hda     -> cdrom
>         vda     -> vda
>         xvda    -> vda
So this looks good.

However... the converted guest does not boot at all. Please see the
attached screenshot (it's not big).

To see whether the issue was introduced by my patch, I rebuilt virt-v2v
with my patch removed (that is, at current master = 1673fc4b640f), and
repeated the conversion (first undefining the "rhel5.11.out" domain).

The boot failure persists, so it's unrelated to the patch.

Is this a known issue?

Does it block merging the patch?

Thanks!
Laszlo

> diff --git a/tests/test-v2v-cdrom.expected b/tests/test-v2v-cdrom.expected
> index 34d2bf5961b0..17bd152d8e64 100644
> --- a/tests/test-v2v-cdrom.expected
> +++ b/tests/test-v2v-cdrom.expected
> @@ -4,5 +4,5 @@
>      </disk>
>      <disk device='cdrom' type='file'>
>        <driver name='qemu' type='raw'/>
> -      <target dev='hdc' bus='ide'/>
> +      <target dev='sdc' bus='sata'/>
>      </disk>
> diff --git a/tests/test-v2v-cdrom.xml.in b/tests/test-v2v-cdrom.xml.in
> index 6bad5eab1cd4..a6e1e3f514d5 100644
> --- a/tests/test-v2v-cdrom.xml.in
> +++ b/tests/test-v2v-cdrom.xml.in
> @@ -35,7 +35,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301 USA.
>        <disk type='file' device='cdrom'>
>          <driver name='qemu' type='raw'/>
>          <source
file='@abs_top_builddir@/test-data/phony-guests/blank-disk.img'/>
> -        <!-- virt-v2v should preserve the device name and bus -->
> +        <!-- virt-v2v should change the bus to sata, due to Windows 7
> +             triggering a machine type change from i440fx to q35. Beyond
that,
> +             virt-v2v should preserve the on-bus index. -->
>          <target dev='hdc' bus='ide'/>
>        </disk>
>      </devices>
> diff --git a/tests/test-v2v-i-ova.xml b/tests/test-v2v-i-ova.xml
> index d7383905fdc0..9f3c1974243f 100644
> --- a/tests/test-v2v-i-ova.xml
> +++ b/tests/test-v2v-i-ova.xml
> @@ -28,7 +28,7 @@
>      </disk>
>      <disk device='cdrom' type='file'>
>        <driver name='qemu' type='raw'/>
> -      <target dev='hda' bus='ide'/>
> +      <target dev='sda' bus='sata'/>
>      </disk>
>      <disk device='floppy' type='file'>
>        <driver name='qemu' type='raw'/>
> 
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On 12/16/21 11:50, Laszlo Ersek wrote:
> However... the converted guest does not boot at all. Please see the
> attached screenshot (it's not big).
Some more details. During the conversion, I get a warning as follows:
> virt-v2v: warning: mount: mount exited with status 32: mount: 
> /sysroot/mnt2: /dev/sda already mounted or mount point busy. (ignored)
The issue seems to be that *before* the code in my patch runs, there is a
separate mapping, from /dev/hda (the CD-ROM) to /dev/sda. However, /dev/sda is
already taken: it represents the (originally virtio-blk) system disk.

Here's the contents of the original /etc/fstab file:
> /dev/VolGroup00/LogVol00 /                       ext3    defaults        1
1
> LABEL=/boot             /boot                   ext3    defaults        1 2
> tmpfs                   /dev/shm                tmpfs   defaults        0 0
> devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
> sysfs                   /sys                    sysfs   defaults        0 0
> proc                    /proc                   proc    defaults        0 0
> /dev/VolGroup00/LogVol01 swap                    swap    defaults        0
0
> /dev/hda                 /mnt2                    iso9660 noauto         0
0
And here's a bit larger snippet from the log:
> libguestfs: trace: v2v: mount "/dev/hda" "/mnt2"
> guestfsd: => mount (0x1) took 0.13 secs
> guestfsd: <= mount (0x1) request length 64 bytes
> device name translated: /dev/hda -> /dev/sda
This seems to come from "daemon/device-name-translation.c" in
libguestfs.

But, I'm attaching the full conversion log too. (NB this log was generated
with my patch applied; however, the patch itself makes no difference regarding
the boot failure, as stated before.)

FWIW, I don't know if this warning (i.e., the failed attempt to mount
/dev/sda) has anything to do with the boot failure in the converted guest.

Thanks,
Laszlo
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