[libvirt] [PATCH v2 10/10] blockcommit: turn on active commit

[Peter Krempa]

On 06/06/14 00:52, Eric Blake wrote:
> With this in place, I can (finally!) now do:
> 
> virsh blockcommit $dom vda --shallow --wait --verbose --pivot
> 
> and watch qemu shorten the backing chain by one, followed by
> libvirt automatically updating the dumpxml output, effectively
> undoing the work of virsh snapshot-commit --no-metadata --disk-only.
> Commit is SOOOO much faster than blockpull, when I'm still fairly
> close in time to when the temporary qcow2 wrapper file was created
> via a snapshot operation!
> 
> * src/qemu/qemu_driver.c (qemuDomainBlockCommit): Implement live
> commit to regular files.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 45 +++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 39 insertions(+), 6 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 5903144..c0fc5e9 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c

> @@ -15540,13 +15542,14 @@ qemuDomainBlockCommit(virDomainPtr dom,
>                                                       &top_parent)))
>          goto endjob;
> 
> -    /* FIXME: qemu 2.0 supports active commit, but as a two-stage
> -     * process; qemu 2.1 is further improving active commit. We need
> -     * to start supporting it in libvirt. */
>      if (topSource == disk->src) {
>          /* We assume that no one will backport qemu 2.0 active commit
>           * to an earlier qemu without also backporting the block job
> -         * ready event; but this makes sure of that fact */
> +         * ready event; but this makes sure of that fact.
> +         *
> +         * XXX Also need to check other capability bit(s): qemu 1.7
> +         * supports async blockjob but not active commit; and qemu 2.0
> +         * active commit misbehaves on 0-byte file.  */
>          if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKJOB_ASYNC)) {
>              virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>                             _("active commit not supported with this QEMU binary"));

ACK once you figure out the detection of the capability.

Peter

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