Commit 808c4b6f authored by Max Reitz's avatar Max Reitz Committed by Stefan Hajnoczi
Browse files

qcow2: Allow "full" discard 



Normally, discarded sectors should read back as zero. However, there are
cases in which a sector (or rather cluster) should be discarded as if
they were never written in the first place, that is, reading them should
fall through to the backing file again.

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: 1414159063-25977-2-git-send-email-mreitz@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 70a5ff6b

block/qcow2-cluster.c

+17 −10
Original line number Diff line number Diff line
@@ -1414,7 +1414,7 @@ int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset) 
 * clusters.

 */

static int discard_single_l2(BlockDriverState *bs, uint64_t offset,

    unsigned int nb_clusters, enum qcow2_discard_type type)

    unsigned int nb_clusters, enum qcow2_discard_type type, bool full_discard)

{

    BDRVQcowState *s = bs->opaque;

    uint64_t *l2_table;
@@ -1436,23 +1436,30 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, 
        old_l2_entry = be64_to_cpu(l2_table[l2_index + i]);



        /*

         * Make sure that a discarded area reads back as zeroes for v3 images

         * (we cannot do it for v2 without actually writing a zero-filled

         * buffer). We can skip the operation if the cluster is already marked

         * as zero, or if it's unallocated and we don't have a backing file.

         * If full_discard is false, make sure that a discarded area reads back

         * as zeroes for v3 images (we cannot do it for v2 without actually

         * writing a zero-filled buffer). We can skip the operation if the

         * cluster is already marked as zero, or if it's unallocated and we

         * don't have a backing file.

         *

         * TODO We might want to use bdrv_get_block_status(bs) here, but we're

         * holding s->lock, so that doesn't work today.

         *

         * If full_discard is true, the sector should not read back as zeroes,

         * but rather fall through to the backing file.

         */

        switch (qcow2_get_cluster_type(old_l2_entry)) {

            case QCOW2_CLUSTER_UNALLOCATED:

                if (!bs->backing_hd) {

                if (full_discard || !bs->backing_hd) {

                    continue;

                }

                break;



            case QCOW2_CLUSTER_ZERO:

                if (!full_discard) {

                    continue;

                }

                break;



            case QCOW2_CLUSTER_NORMAL:

            case QCOW2_CLUSTER_COMPRESSED:
@@ -1464,7 +1471,7 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, 


        /* First remove L2 entries */

        qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);

        if (s->qcow_version >= 3) {

        if (!full_discard && s->qcow_version >= 3) {

            l2_table[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);

        } else {

            l2_table[l2_index + i] = cpu_to_be64(0);
@@ -1483,7 +1490,7 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, 
}



int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,

    int nb_sectors, enum qcow2_discard_type type)

    int nb_sectors, enum qcow2_discard_type type, bool full_discard)

{

    BDRVQcowState *s = bs->opaque;

    uint64_t end_offset;
@@ -1506,7 +1513,7 @@ int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, 


    /* Each L2 table is handled by its own loop iteration */

    while (nb_clusters > 0) {

        ret = discard_single_l2(bs, offset, nb_clusters, type);

        ret = discard_single_l2(bs, offset, nb_clusters, type, full_discard);

        if (ret < 0) {

            goto fail;

        }

block/qcow2-snapshot.c

+1 −1
Original line number Diff line number Diff line
@@ -441,7 +441,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info) 
    qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),

                           align_offset(sn->vm_state_size, s->cluster_size)

                                >> BDRV_SECTOR_BITS,

                           QCOW2_DISCARD_NEVER);

                           QCOW2_DISCARD_NEVER, false);



#ifdef DEBUG_ALLOC

    {

block/qcow2.c

+1 −1
Original line number Diff line number Diff line
@@ -2089,7 +2089,7 @@ static coroutine_fn int qcow2_co_discard(BlockDriverState *bs, 


    qemu_co_mutex_lock(&s->lock);

    ret = qcow2_discard_clusters(bs, sector_num << BDRV_SECTOR_BITS,

        nb_sectors, QCOW2_DISCARD_REQUEST);

        nb_sectors, QCOW2_DISCARD_REQUEST, false);

    qemu_co_mutex_unlock(&s->lock);

    return ret;

}

block/qcow2.h

+1 −1
Original line number Diff line number Diff line
@@ -534,7 +534,7 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs, 


int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m);

int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,

    int nb_sectors, enum qcow2_discard_type type);

    int nb_sectors, enum qcow2_discard_type type, bool full_discard);

int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors);



int qcow2_expand_zero_clusters(BlockDriverState *bs);