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| author | Vladimir Sementsov-Ogievskiy | 2020-05-28 11:44:04 +0200 |
|---|---|---|
| committer | Max Reitz | 2020-07-06 10:34:14 +0200 |
| commit | a2adbbf603cee443ca923f6e8546267a706567d5 (patch) | |
| tree | db3c6df1347a108d1a39791cf8a3a8b22c9fee6a /include/block | |
| parent | block/vhdx: drop unallocated_blocks_are_zero (diff) | |
| download | qemu-a2adbbf603cee443ca923f6e8546267a706567d5.tar.gz qemu-a2adbbf603cee443ca923f6e8546267a706567d5.tar.xz qemu-a2adbbf603cee443ca923f6e8546267a706567d5.zip | |
block: drop unallocated_blocks_are_zero
Currently this field only set by qed and qcow2. But in fact, all
backing-supporting formats (parallels, qcow, qcow2, qed, vmdk) share
these semantics: on unallocated blocks, if there is no backing file they
just memset the buffer with zeroes.
So, document this behavior for .supports_backing and drop
.unallocated_blocks_are_zero
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200528094405.145708-10-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'include/block')
| -rw-r--r-- | include/block/block.h | 5 | ||||
| -rw-r--r-- | include/block/block_int.h | 12 |
2 files changed, 11 insertions, 6 deletions
diff --git a/include/block/block.h b/include/block/block.h index e7934e07f2..bca3bb831c 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -22,11 +22,6 @@ typedef struct BlockDriverInfo { int64_t vm_state_offset; bool is_dirty; /* - * True if unallocated blocks read back as zeroes. This is equivalent - * to the LBPRZ flag in the SCSI logical block provisioning page. - */ - bool unallocated_blocks_are_zero; - /* * True if this block driver only supports compressed writes */ bool needs_compressed_writes; diff --git a/include/block/block_int.h b/include/block/block_int.h index 1b86b59af1..3d6cf88592 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -123,7 +123,17 @@ struct BlockDriver { */ bool bdrv_needs_filename; - /* Set if a driver can support backing files */ + /* + * Set if a driver can support backing files. This also implies the + * following semantics: + * + * - Return status 0 of .bdrv_co_block_status means that corresponding + * blocks are not allocated in this layer of backing-chain + * - For such (unallocated) blocks, read will: + * - fill buffer with zeros if there is no backing file + * - read from the backing file otherwise, where the block layer + * takes care of reading zeros beyond EOF if backing file is short + */ bool supports_backing; /* For handling image reopen for split or non-split files */ |