Re: [Xen-devel] [PATCH v6] libxl: allow 'phy' backend to use empty files

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Wed, Feb 17, 2016 at 5:20 PM, Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
> This was introduced by 97ee1f (~5 years ago), but was probably never
> surfaced because most people used regular files as CDROM images, so the PHY
> backend was actually never selected. A year ago this was changed, and now
> regular RAW files are also handled by the PHY backend, which has made this
> bug surface.
>
> Fix it by allowing empty disks to use the PHY backend, skipping the stat
> tests.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Reported-by: Alex Braunegg <alex.braunegg@xxxxxxxxx>

So first of all, it's not 100% clear from this commit what the problem
was that Alex reported.  I take it that if he used a phy backend for a
cdrom, that "xl cd-eject" failed?

Unfortunately, after this changeset, creating a VM with an empty cdrom
fails, because it tries to run the block script and the block script
fails:

# cat c6-01.cfg
builder="hvm"
name = "c6-01"
memory = "2048"
disk = [ 
'format=raw,vdev=sda,target=/images/c6-01.raw','vdev=hdc,access=ro,devtype=cdrom'
]
vif = [ 'mac=5a:39:bb:b6:84:b4' ]
vcpus=1
on_crash = 'destroy'
serial='pty'
# xl create c6-01.cfg
libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus:
/etc/xen/scripts/block add [7236] exited with error status 1
libxl: error: libxl_device.c:1114:device_hotplug_child_death_cb:
script: /etc/xen/scripts/block failed; error detected.
libxl: error: libxl_create.c:1247:domcreate_launch_dm: unable to add
disk devices
libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus:
/etc/xen/scripts/block remove [7319] exited with error status 1
libxl: error: libxl_device.c:1114:device_hotplug_child_death_cb:
script: /etc/xen/scripts/block failed; error detected.
libxl: error: libxl.c:1565:libxl__destroy_domid: non-existant domain 5
libxl: error: libxl.c:1523:domain_destroy_callback: unable to destroy
guest with domid 5
libxl: error: libxl.c:1452:domain_destroy_cb: destruction of domain 5 failed

 -George

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