Commit f01643fb authored by Kevin Wolf's avatar Kevin Wolf
Browse files

qcow2: Support BDRV_REQ_ZERO_WRITE for truncate 



If BDRV_REQ_ZERO_WRITE is set and we're extending the image, calling
qcow2_cluster_zeroize() with flags=0 does the right thing: It doesn't
undo any previous preallocation, but just adds the zero flag to all
relevant L2 entries. If an external data file is in use, a write_zeroes
request to the data file is made instead.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-Id: <20200424125448.63318-5-kwolf@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 8c6242b6

block/qcow2-cluster.c

+1 −1
Original line number Diff line number Diff line
@@ -1795,7 +1795,7 @@ int qcow2_cluster_zeroize(BlockDriverState *bs, uint64_t offset, 
    /* Caller must pass aligned values, except at image end */

    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));

    assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||

           end_offset == bs->total_sectors << BDRV_SECTOR_BITS);

           end_offset >= bs->total_sectors << BDRV_SECTOR_BITS);



    /* The zero flag is only supported by version 3 and newer */

    if (s->qcow_version < 3) {

block/qcow2.c

+34 −0
Original line number Diff line number Diff line
@@ -1726,6 +1726,7 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options, 


    bs->supported_zero_flags = header.version >= 3 ?

                               BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK : 0;

    bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;



    /* Repair image if dirty */

    if (!(flags & (BDRV_O_CHECK | BDRV_O_INACTIVE)) && !bs->read_only &&
@@ -4214,6 +4215,39 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset, 
        g_assert_not_reached();

    }



    if ((flags & BDRV_REQ_ZERO_WRITE) && offset > old_length) {

        uint64_t zero_start = QEMU_ALIGN_UP(old_length, s->cluster_size);



        /*

         * Use zero clusters as much as we can. qcow2_cluster_zeroize()

         * requires a cluster-aligned start. The end may be unaligned if it is

         * at the end of the image (which it is here).

         */

        ret = qcow2_cluster_zeroize(bs, zero_start, offset - zero_start, 0);

        if (ret < 0) {

            error_setg_errno(errp, -ret, "Failed to zero out new clusters");

            goto fail;

        }



        /* Write explicit zeros for the unaligned head */

        if (zero_start > old_length) {

            uint64_t len = zero_start - old_length;

            uint8_t *buf = qemu_blockalign0(bs, len);

            QEMUIOVector qiov;

            qemu_iovec_init_buf(&qiov, buf, len);



            qemu_co_mutex_unlock(&s->lock);

            ret = qcow2_co_pwritev_part(bs, old_length, len, &qiov, 0, 0);

            qemu_co_mutex_lock(&s->lock);



            qemu_vfree(buf);

            if (ret < 0) {

                error_setg_errno(errp, -ret, "Failed to zero out the new area");

                goto fail;

            }

        }

    }



    if (prealloc != PREALLOC_MODE_OFF) {

        /* Flush metadata before actually changing the image size */

        ret = qcow2_write_caches(bs);