Re: [libvirt] Mystery of qemu being unable to open NBD Unix domain socket in current directory
On 06/06/2018 12:29 PM, Richard W.M. Jones wrote:
I'm chasing down a very frustrating bug which only happens on
i686 &
Koji during the nbdkit tests and seemingly nowhere else. Anyway this
is what I've been able to put together:
The libguestfs appliance (guest) is created with this XML snippet:
<disk device="disk" type="network">
<source protocol="nbd">
<host transport="unix" socket="cow.sock"/>
Have you tried an absolute path?
At this point I don't really have any ideas. Does libvirt now
run
qemu in a different directory? Does the error message mean something
else apart from the file not existing?
Libvirtd does chdir("/") early on, so likely qemu is run with / (rather
than the original current working directory) as its root. So an absolute
path should fix things.
2018-06-06T17:02:54.450507Z qemu-system-i386: -drive
file=nbd+unix://?socket=cow.sock,format=raw,if=none,id=drive-scsi0-0-0-0,cache=writeback:
Failed to connect socket cow.sock: No such file or directory
Also the nbd+unix syntax doesn't appear to be documented in qemu.
Is this a new thing? Normally we use nbd:unix:...
nbd:unix:... is the old-style legacy form, nbd+unix:// is the URI style.
The URI style is a bit more flexible (you can add options without
having to add more ad-hoc parsing). Ideally, we'll be moving libvirt to
an even newer -blockdev style (which can either directly use the JSON
you'd hand to QMP blockdev-add, or which uses a dotted syntax similar to
-drive); that's been an ongoing task for Peter. As for lack of
documentation in qemu, I'm not surprised.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org