Commit a980c98c authored by Kevin Wolf's avatar Kevin Wolf Committed by Anthony Liguori
Browse files

qcow2: Update multiple refcounts at once 



Don't write each single changed refcount block entry to the disk after it is
written, but update all entries of the block and write all of them at once.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent 44ff42de

block/qcow2.c

+36 −4
Original line number Diff line number Diff line
@@ -2578,6 +2578,9 @@ static int update_refcount(BlockDriverState *bs, 
{

    BDRVQcowState *s = bs->opaque;

    int64_t start, last, cluster_offset;

    int64_t refcount_block_offset = 0;

    int64_t table_index = -1, old_table_index;

    int first_index = -1, last_index = -1;



#ifdef DEBUG_ALLOC2

    printf("update_refcount: offset=%lld size=%lld addend=%d\n",
@@ -2590,10 +2593,25 @@ static int update_refcount(BlockDriverState *bs, 
    for(cluster_offset = start; cluster_offset <= last;

        cluster_offset += s->cluster_size)

    {

        int64_t refcount_block_offset;

        int block_index, refcount;

        int64_t cluster_index = cluster_offset >> s->cluster_bits;



        /* Only write refcount block to disk when we are done with it */

        old_table_index = table_index;

        table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);

        if ((old_table_index >= 0) && (table_index != old_table_index)) {

            size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;

            if (bdrv_pwrite(s->hd,

                refcount_block_offset + (first_index << REFCOUNT_SHIFT),

                &s->refcount_block_cache[first_index], size) != size)

            {

                return -EIO;

            }



            first_index = -1;

            last_index = -1;

        }



        /* Load the refcount block and allocate it if needed */

        refcount_block_offset = alloc_refcount_block(bs, cluster_index);

        if (refcount_block_offset < 0) {
@@ -2603,6 +2621,13 @@ static int update_refcount(BlockDriverState *bs, 
        /* we can update the count and save it */

        block_index = cluster_index &

            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);

        if (first_index == -1 || block_index < first_index) {

            first_index = block_index;

        }

        if (block_index > last_index) {

            last_index = block_index;

        }



        refcount = be16_to_cpu(s->refcount_block_cache[block_index]);

        refcount += addend;

        if (refcount < 0 || refcount > 0xffff)
@@ -2611,12 +2636,19 @@ static int update_refcount(BlockDriverState *bs, 
            s->free_cluster_index = cluster_index;

        }

        s->refcount_block_cache[block_index] = cpu_to_be16(refcount);

    }



    /* Write last changed block to disk */

    if (refcount_block_offset != 0) {

        size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;

        if (bdrv_pwrite(s->hd,

                        refcount_block_offset + (block_index << REFCOUNT_SHIFT),

                        &s->refcount_block_cache[block_index], 2) != 2)

            refcount_block_offset + (first_index << REFCOUNT_SHIFT),

            &s->refcount_block_cache[first_index], size) != size)

        {

            return -EIO;



        }

    }



    return 0;

}