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https://bugzilla.redhat.com/show_bug.cgi?id=1140981 reports that the qemu-kvm shipped as part of RHEL 7.0 intentionally[1] cripples block jobs by removing the 'block-stream' QMP command, while still leaving 'block-job-cancel' as an unusable no-op. Meanwhile, we already had existing code that checked whether block jobs were completely missing (such as qemu 0.15), old style (cancel is synchronous, and all commands spelled with '_'), or new style (cancel is asynchronous, and all commands spelled with '-'), and used that three-way probe to give decent error messages. At the time that code was added, all existing qemu versions fell in one of three buckets, and the code was using the presence of 'block-job-cancel' as the witness of which of the three buckets. But now that RHEL qemu has shipped with intentionally crippled 'block-stream', we have a fourth bucket, which results in ugly error messages when trying 'virsh blockpull': error: Requested operation is not valid: Command 'block-stream' is not found In reality, the fourth bucket should be treated the same as the first bucket (no block job support); we can do that by realizing that no existing build of qemu has working block-stream while lacking block-job-cancel, so it is easiest to change our witness to the command that starts a job rather than ends one. We still act correctly regarding command spelling and whether cancel is asynchronous. And on crippled RHEL builds, we now get the desired: error: unsupported configuration: block jobs not supported with this qemu binary [1] The intentional cripple is limited to qemu-kvm of RHEL; when using qemu-kvm-rhev of RHEV, block job functionality is supported. Don't ask me to explain the "why" behind it all - I'm just dealing with fallout from someone else's decision. * src/qemu/qemu_capabilities.h (QEMU_CAPS_BLOCKJOB_SYNC): Tweak comment. * src/qemu/qemu_capabilities.c (virQEMUCapsCommands): Look for stream rather than cancel when determining the flavor of block jobs supported. Signed-off-by: Eric Blake <eblake@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>