Commit a2adbbf6 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Max Reitz
Browse files

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: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Message-Id: <20200528094405.145708-10-vsementsov@virtuozzo.com>
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent cdf9ebf1

block/io.c

+2 −7
Original line number Diff line number Diff line
@@ -2406,7 +2406,7 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs, 


    if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {

        ret |= BDRV_BLOCK_ALLOCATED;

    } else if (want_zero) {

    } else if (want_zero && bs->drv->supports_backing) {

        if (bs->backing) {

            BlockDriverState *bs2 = bs->backing->bs;

            int64_t size2 = bdrv_getlength(bs2);
@@ -2415,14 +2415,9 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs, 
                ret |= BDRV_BLOCK_ZERO;

            }

        } else {

            BlockDriverInfo bdi;

            int ret2 = bdrv_get_info(bs, &bdi);



            if (ret2 == 0 && bdi.unallocated_blocks_are_zero) {

            ret |= BDRV_BLOCK_ZERO;

        }

    }

    }



    if (want_zero && ret & BDRV_BLOCK_RECURSE &&

        local_file && local_file != bs &&

block/qcow2.c

+0 −1
Original line number Diff line number Diff line
@@ -4987,7 +4987,6 @@ err: 
static int qcow2_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)

{

    BDRVQcow2State *s = bs->opaque;

    bdi->unallocated_blocks_are_zero = true;

    bdi->cluster_size = s->cluster_size;

    bdi->vm_state_offset = qcow2_vm_state_offset(s);

    return 0;

block/qed.c

+0 −1
Original line number Diff line number Diff line
@@ -1514,7 +1514,6 @@ static int bdrv_qed_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) 
    memset(bdi, 0, sizeof(*bdi));

    bdi->cluster_size = s->header.cluster_size;

    bdi->is_dirty = s->header.features & QED_F_NEED_CHECK;

    bdi->unallocated_blocks_are_zero = true;

    return 0;

}

include/block/block.h

+0 −5
Original line number Diff line number Diff line
@@ -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

     */

include/block/block_int.h

+11 −1
Original line number Diff line number Diff line
@@ -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 */