On 09/10/2014 02:54 AM, Fam Zheng wrote: >> Let's think of a situation that recursive blockers protect but >> backing_blocker does not: >> >> a <- b <- c <- d >> >> c is the backing file and is therefore protected by the op blocker. >> >> The block-commit command works with node-names, however, so we can >> manipulate any nodes in the graph, not just the topmost one. Try this: >> >> block-commit d >> block-commit b >> >> I haven't checked yet but I suspect it will launch two block-commit jobs >> on the same partial chain (that's a bad thing because it can lead to >> corruption). > > 1) Does block-commit work with node-names already? In other words, is > block-commit b possible now? I only see drive-mirror works with it, but not > drive-backup, block-mirror or block-commit.
IIRC, Jeff Cody proposed patches for qemu 2.1 that would have done this,
but we dropped them for that release in order to get the recursive
blockers sorted out first.
>
> 2) Regardless of the answer to 1), I think we could use a similar approach as
> drive-backup here: split BLOCK_OP_TYPE_COMMIT to
> BLOCK_OP_TYPE_COMMIT_{SOURCE,TARGET}, and only unblock
> BLOCK_OP_TYPE_COMMIT_TARGET in bdrv_set_backing_hd.
In that earlier thread, Jeff had some ideas that it is not so much the
operation name that should be the blocker, but the lower-level action(s)
implied by each operation (read metadata, write metadata, read image,
write image)
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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