qemu-img: rebase: Reduce reads on in-chain rebase
In the following case: (base) A <- B <- C (tip) when running: qemu-img rebase -b A C QEMU would read all sectors not allocated in the file being rebased (C) and compare them to the new base image (A), regardless of whether they were changed or even allocated anywhere along the chain between the new base and the top image (B). This causes many unneeded reads when rebasing an image which represents a small diff of a large disk, as it would read most of the disk's sectors. Instead, use bdrv_is_allocated_above() to reduce the number of unnecessary reads. Reviewed-by:Karl Heubaum <karl.heubaum@oracle.com> Signed-off-by:
Sam Eiderman <shmuel.eiderman@oracle.com> Signed-off-by:
Eyal Moscovici <eyal.moscovici@oracle.com> Message-id: 20190523163337.4497-3-shmuel.eiderman@oracle.com Signed-off-by:
Max Reitz <mreitz@redhat.com>
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