Commit db933fbe authored by Lidong Chen's avatar Lidong Chen Committed by Max Reitz
Browse files

qemu-img: use blk_co_pwrite_zeroes for zero sectors when compressed 



When the buffer is zero, blk_co_pwrite_zeroes is more effective than
blk_co_pwritev with BDRV_REQ_WRITE_COMPRESSED. This patch can reduce
the time for converting qcow2 images with lots of zero data.

Signed-off-by: default avatarLidong Chen <lidongchen@tencent.com>
Message-id: 1493261907-18734-1-git-send-email-lidongchen@tencent.com
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 9f1b92ad

qemu-img.c

+14 −30
Original line number Diff line number Diff line
@@ -1649,6 +1649,8 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num, 


    while (nb_sectors > 0) {

        int n = nb_sectors;

        BdrvRequestFlags flags = s->compressed ? BDRV_REQ_WRITE_COMPRESSED : 0;



        switch (status) {

        case BLK_BACKING_FILE:

            /* If we have a backing file, leave clusters unallocated that are
@@ -1658,43 +1660,24 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num, 
            break;



        case BLK_DATA:

            /* We must always write compressed clusters as a whole, so don't

             * try to find zeroed parts in the buffer. We can only save the

             * write if the buffer is completely zeroed and we're allowed to

             * keep the target sparse. */

            if (s->compressed) {

                if (s->has_zero_init && s->min_sparse &&

                    buffer_is_zero(buf, n * BDRV_SECTOR_SIZE))

                {

                    assert(!s->target_has_backing);

                    break;

                }



                iov.iov_base = buf;

                iov.iov_len = n << BDRV_SECTOR_BITS;

                qemu_iovec_init_external(&qiov, &iov, 1);



                ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,

                                     n << BDRV_SECTOR_BITS, &qiov,

                                     BDRV_REQ_WRITE_COMPRESSED);

                if (ret < 0) {

                    return ret;

                }

                break;

            }



            /* If there is real non-zero data or we're told to keep the target

             * fully allocated (-S 0), we must write it. Otherwise we can treat

             * it as zero sectors. */

            /* If we're told to keep the target fully allocated (-S 0) or there

             * is real non-zero data, we must write it. Otherwise we can treat

             * it as zero sectors.

             * Compressed clusters need to be written as a whole, so in that

             * case we can only save the write if the buffer is completely

             * zeroed. */

            if (!s->min_sparse ||

                is_allocated_sectors_min(buf, n, &n, s->min_sparse))

                (!s->compressed &&

                 is_allocated_sectors_min(buf, n, &n, s->min_sparse)) ||

                (s->compressed &&

                 !buffer_is_zero(buf, n * BDRV_SECTOR_SIZE)))

            {

                iov.iov_base = buf;

                iov.iov_len = n << BDRV_SECTOR_BITS;

                qemu_iovec_init_external(&qiov, &iov, 1);



                ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,

                                     n << BDRV_SECTOR_BITS, &qiov, 0);

                                     n << BDRV_SECTOR_BITS, &qiov, flags);

                if (ret < 0) {

                    return ret;

                }
@@ -1704,6 +1687,7 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num, 


        case BLK_ZERO:

            if (s->has_zero_init) {

                assert(!s->target_has_backing);

                break;

            }

            ret = blk_co_pwrite_zeroes(s->target,