mirror of https://gitee.com/openkylin/qemu.git
qcow2: Catch more unaligned write_zero into zero cluster
is_zero_cluster() and is_zero_cluster_top_locked() are used only by qcow2_co_write_zeroes(). The former is too broad (we don't care if the sectors we are about to overwrite are non-zero, only that all other sectors in the cluster are zero), so it needs to be called up to twice but with smaller limits - rename it along with adding the neeeded parameter. The latter can be inlined for more compact code. The testsuite change shows that we now have a sparser top file when an unaligned write_zeroes overwrites the only portion of the backing file with data. Based on a patch proposal by Denis V. Lunev. CC: Denis V. Lunev <den@openvz.org> Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Denis V. Lunev <den@openvz.org> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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@ -2406,26 +2406,19 @@ finish:
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}
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static bool is_zero_cluster(BlockDriverState *bs, int64_t start)
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static bool is_zero_sectors(BlockDriverState *bs, int64_t start,
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uint32_t count)
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{
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BDRVQcow2State *s = bs->opaque;
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int nr;
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BlockDriverState *file;
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int64_t res = bdrv_get_block_status_above(bs, NULL, start,
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s->cluster_sectors, &nr, &file);
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return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == s->cluster_sectors;
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}
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int64_t res;
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static bool is_zero_cluster_top_locked(BlockDriverState *bs, int64_t start)
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{
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BDRVQcow2State *s = bs->opaque;
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int nr = s->cluster_sectors;
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uint64_t off;
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int ret;
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ret = qcow2_get_cluster_offset(bs, start << BDRV_SECTOR_BITS, &nr, &off);
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assert(nr == s->cluster_sectors);
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return ret == QCOW2_CLUSTER_UNALLOCATED || ret == QCOW2_CLUSTER_ZERO;
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if (!count) {
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return true;
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}
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res = bdrv_get_block_status_above(bs, NULL, start, count,
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&nr, &file);
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return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == count;
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}
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static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
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@ -2434,27 +2427,33 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
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int ret;
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BDRVQcow2State *s = bs->opaque;
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int head = sector_num % s->cluster_sectors;
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int tail = (sector_num + nb_sectors) % s->cluster_sectors;
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uint32_t head = sector_num % s->cluster_sectors;
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uint32_t tail = (sector_num + nb_sectors) % s->cluster_sectors;
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trace_qcow2_write_zeroes_start_req(qemu_coroutine_self(), sector_num,
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nb_sectors);
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if (head != 0 || tail != 0) {
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if (head || tail) {
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int64_t cl_start = sector_num - head;
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uint64_t off;
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int nr;
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assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors);
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sector_num = cl_start;
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nb_sectors = s->cluster_sectors;
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if (!is_zero_cluster(bs, sector_num)) {
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/* check whether remainder of cluster already reads as zero */
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if (!(is_zero_sectors(bs, cl_start, head) &&
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is_zero_sectors(bs, sector_num + nb_sectors,
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-tail & (s->cluster_sectors - 1)))) {
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return -ENOTSUP;
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}
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qemu_co_mutex_lock(&s->lock);
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/* We can have new write after previous check */
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if (!is_zero_cluster_top_locked(bs, sector_num)) {
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sector_num = cl_start;
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nb_sectors = nr = s->cluster_sectors;
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ret = qcow2_get_cluster_offset(bs, cl_start << BDRV_SECTOR_BITS,
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&nr, &off);
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if (ret != QCOW2_CLUSTER_UNALLOCATED && ret != QCOW2_CLUSTER_ZERO) {
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qemu_co_mutex_unlock(&s->lock);
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return -ENOTSUP;
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}
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@ -102,13 +102,13 @@ wrote 2048/2048 bytes at offset 29696
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read 4096/4096 bytes at offset 28672
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4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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[{ "start": 0, "length": 4096, "depth": 1, "zero": true, "data": false},
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{ "start": 4096, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 20480},
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{ "start": 4096, "length": 4096, "depth": 0, "zero": true, "data": false},
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{ "start": 8192, "length": 4096, "depth": 1, "zero": true, "data": false},
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{ "start": 12288, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 24576},
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{ "start": 12288, "length": 4096, "depth": 0, "zero": true, "data": false},
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{ "start": 16384, "length": 4096, "depth": 1, "zero": true, "data": false},
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{ "start": 20480, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 28672},
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{ "start": 20480, "length": 4096, "depth": 0, "zero": true, "data": false},
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{ "start": 24576, "length": 4096, "depth": 1, "zero": true, "data": false},
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{ "start": 28672, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 32768},
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{ "start": 28672, "length": 4096, "depth": 0, "zero": true, "data": false},
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{ "start": 32768, "length": 134184960, "depth": 1, "zero": true, "data": false}]
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== spanning two clusters, non-zero before request ==
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