Commit 491d27e2 authored by Max Reitz's avatar Max Reitz Committed by Stefan Hajnoczi
Browse files

qcow2: Implement bdrv_make_empty() 



Implement this function by making all clusters in the image file fall
through to the backing file (by using the recently extended discard).

Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-id: 1414159063-25977-3-git-send-email-mreitz@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 808c4b6f

block/qcow2.c

+27 −0
Original line number Diff line number Diff line
@@ -2230,6 +2230,32 @@ fail: 
    return ret;

}



static int qcow2_make_empty(BlockDriverState *bs)

{

    int ret = 0;

    uint64_t start_sector;

    int sector_step = INT_MAX / BDRV_SECTOR_SIZE;



    for (start_sector = 0; start_sector < bs->total_sectors;

         start_sector += sector_step)

    {

        /* As this function is generally used after committing an external

         * snapshot, QCOW2_DISCARD_SNAPSHOT seems appropriate. Also, the

         * default action for this kind of discard is to pass the discard,

         * which will ideally result in an actually smaller image file, as

         * is probably desired. */

        ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE,

                                     MIN(sector_step,

                                         bs->total_sectors - start_sector),

                                     QCOW2_DISCARD_SNAPSHOT, true);

        if (ret < 0) {

            break;

        }

    }



    return ret;

}



static coroutine_fn int qcow2_co_flush_to_os(BlockDriverState *bs)

{

    BDRVQcowState *s = bs->opaque;
@@ -2676,6 +2702,7 @@ static BlockDriver bdrv_qcow2 = { 
    .bdrv_co_discard        = qcow2_co_discard,

    .bdrv_truncate          = qcow2_truncate,

    .bdrv_write_compressed  = qcow2_write_compressed,

    .bdrv_make_empty        = qcow2_make_empty,



    .bdrv_snapshot_create   = qcow2_snapshot_create,

    .bdrv_snapshot_goto     = qcow2_snapshot_goto,