From a2adbbf603cee443ca923f6e8546267a706567d5 Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Thu, 28 May 2020 12:44:04 +0300 Subject: 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 Reviewed-by: Eric Blake Message-Id: <20200528094405.145708-10-vsementsov@virtuozzo.com> Signed-off-by: Max Reitz --- include/block/block.h | 5 ----- include/block/block_int.h | 12 +++++++++++- 2 files changed, 11 insertions(+), 6 deletions(-) (limited to 'include/block') 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 @@ -21,11 +21,6 @@ typedef struct BlockDriverInfo { /* offset at which the VM state can be saved (0 if not possible) */ 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 */ 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 */ -- cgit v1.2.3-55-g7522