Re: [Libguestfs] [Qemu-devel] [Qemu-block] [PATCH] tests: regressions: make test-big-heap use a temporary empty file
On 03/21/2018 03:44 PM, Kevin Wolf wrote:
>>
>> You're right that file locking on a character device like /dev/null is
>> not going to work as expected, but is it a case where fcntl() actually
>> fails, or is it worse where the fcntl() claiming the locks "succeeds"
>> but doesn't do what we want? That is, what were the actual error
>> messages you ran into?
>
> $ qemu-img --version
> qemu-img version 2.10.1(qemu-2.10.1-2.fc27)
> Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
> $ qemu-img info /dev/null
> qemu-img: Could not open '/dev/null': Failed to get "consistent
read" lock
> Is another process using the image?
Not sure where the difference is, but I can't reproduce this on
upstream, neither git master nor the v2.10.1 tag:
Is it a case where file locking actually works, and more than one
process is trying to lock /dev/null at once? (qemu-img info is
short-lived, but could there be another longer-lived process also using
/dev/null)?
Does using -r help (if the only reason you're telling qemu-img to
operate on /dev/null is to probe qemu-img features, can you probe those
same features without needing to write, which in turn requests less
locking)?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org