[libvirt] [PATCH v2] qemu: better error message when block job can't succeed

[Eric Blake]

On 10/24/2014 02:56 PM, Eric Blake wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1140981 reports that
> the qemu-kvm shipped as part of RHEL 7.0 intentionally cripples
> block jobs by removing the 'block-stream' QMP command, but that
> our probe for whether block jobs work was merely whether
> 'block-job-cancel' exists.  As the crippling did not remove
> job cancellation, we end up trying the qemu command and printing
> an ugly message:
> 
>  error: Requested operation is not valid: Command 'block-stream' is not found
> 
> even though our code base was already prepared to print a nice
> message that jobs are unsupported:
> 
>  error: unsupported configuration: block jobs not supported with this qemu binary
> 
> Doing one more QMP probe lets us match the reality of crippled qemu.
> Yes, we really have to cater to two spellings of the command, due to
> older upstream qemu.
> 
> * src/qemu/qemu_capabilities.h (QEMU_CAPS_BLOCK_STREAM): New probe.
> * src/qemu/qemu_capabilities.c (virQEMUCapsProbeQMPCommands): Kill
> block jobs with nice error message if qemu is crippled.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/qemu/qemu_capabilities.c | 11 +++++++++++
>  src/qemu/qemu_capabilities.h |  1 +
>  2 files changed, 12 insertions(+)

Even smaller diffstat proposed as v3:
https://www.redhat.com/archives/libvir-list/2014-October/msg00882.html

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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