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authorVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>2019-04-08 19:26:17 +0300
committerKevin Wolf <kwolf@redhat.com>2019-06-04 15:20:41 +0200
commit69f47505ee66afaa513305de0c1895a224e52c45 (patch)
treef29ed60f4b179a51957861bebae2b234f8cf8749 /crypto/cipher.c
parent52f2b8961409be834abaee5189bff2cc9e372851 (diff)
downloadqemu-69f47505ee66afaa513305de0c1895a224e52c45.zip
block: avoid recursive block_status call if possible
drv_co_block_status digs bs->file for additional, more accurate search for hole inside region, reported as DATA by bs since 5daa74a6ebc. This accuracy is not free: assume we have qcow2 disk. Actually, qcow2 knows, where are holes and where is data. But every block_status request calls lseek additionally. Assume a big disk, full of data, in any iterative copying block job (or img convert) we'll call lseek(HOLE) on every iteration, and each of these lseeks will have to iterate through all metadata up to the end of file. It's obviously ineffective behavior. And for many scenarios we don't need this lseek at all. However, lseek is needed when we have metadata-preallocated image. So, let's detect metadata-preallocation case and don't dig qcow2's protocol file in other cases. The idea is to compare allocation size in POV of filesystem with allocations size in POV of Qcow2 (by refcounts). If allocation in fs is significantly lower, consider it as metadata-preallocation case. 102 iotest changed, as our detector can't detect shrinked file as metadata-preallocation, which don't seem to be wrong, as with metadata preallocation we always have valid file length. Two other iotests have a slight change in their QMP output sequence: Active 'block-commit' returns earlier because the job coroutine yields earlier on a blocking operation. This operation is loading the refcount blocks in qcow2_detect_metadata_preallocation(). Suggested-by: Denis V. Lunev <den@openvz.org> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'crypto/cipher.c')
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