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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>
This commit is contained in:
Eric Blake 2016-05-25 21:48:49 -06:00 committed by Kevin Wolf
parent 31ad4fdf91
commit ebb718a5c7
2 changed files with 27 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
block/qcow2.c
View File

@ -2406,26 +2406,19 @@ finish:
}
static bool is_zero_cluster(BlockDriverState *bs, int64_t start)
static bool is_zero_sectors(BlockDriverState *bs, int64_t start,
uint32_t count)
{
BDRVQcow2State *s = bs->opaque;
int nr;
BlockDriverState *file;
int64_t res = bdrv_get_block_status_above(bs, NULL, start,
s->cluster_sectors, &nr, &file);
return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == s->cluster_sectors;
int64_t res;
if (!count) {
return true;
}
static bool is_zero_cluster_top_locked(BlockDriverState *bs, int64_t start)
{
BDRVQcow2State *s = bs->opaque;
int nr = s->cluster_sectors;
uint64_t off;
int ret;
ret = qcow2_get_cluster_offset(bs, start << BDRV_SECTOR_BITS, &nr, &off);
assert(nr == s->cluster_sectors);
return ret == QCOW2_CLUSTER_UNALLOCATED || ret == QCOW2_CLUSTER_ZERO;
res = bdrv_get_block_status_above(bs, NULL, start, count,
&nr, &file);
return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == count;
}
static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
@ -2434,27 +2427,33 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
int ret;
BDRVQcow2State *s = bs->opaque;
int head = sector_num % s->cluster_sectors;
int tail = (sector_num + nb_sectors) % s->cluster_sectors;
uint32_t head = sector_num % s->cluster_sectors;
uint32_t tail = (sector_num + nb_sectors) % s->cluster_sectors;
trace_qcow2_write_zeroes_start_req(qemu_coroutine_self(), sector_num,
nb_sectors);
if (head != 0 || tail != 0) {
if (head || tail) {
int64_t cl_start = sector_num - head;
uint64_t off;
int nr;
assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors);
sector_num = cl_start;
nb_sectors = s->cluster_sectors;
if (!is_zero_cluster(bs, sector_num)) {
/* check whether remainder of cluster already reads as zero */
if (!(is_zero_sectors(bs, cl_start, head) &&
is_zero_sectors(bs, sector_num + nb_sectors,
-tail & (s->cluster_sectors - 1)))) {
return -ENOTSUP;
}
qemu_co_mutex_lock(&s->lock);
/* We can have new write after previous check */
if (!is_zero_cluster_top_locked(bs, sector_num)) {
sector_num = cl_start;
nb_sectors = nr = s->cluster_sectors;
ret = qcow2_get_cluster_offset(bs, cl_start << BDRV_SECTOR_BITS,
&nr, &off);
if (ret != QCOW2_CLUSTER_UNALLOCATED && ret != QCOW2_CLUSTER_ZERO) {
qemu_co_mutex_unlock(&s->lock);
return -ENOTSUP;
}

8
tests/qemu-iotests/154.out
View File

@ -102,13 +102,13 @@ wrote 2048/2048 bytes at offset 29696
read 4096/4096 bytes at offset 28672
4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
[{ "start": 0, "length": 4096, "depth": 1, "zero": true, "data": false},
{ "start": 4096, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 20480},
{ "start": 4096, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 8192, "length": 4096, "depth": 1, "zero": true, "data": false},
{ "start": 12288, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 24576},
{ "start": 12288, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 16384, "length": 4096, "depth": 1, "zero": true, "data": false},
{ "start": 20480, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 28672},
{ "start": 20480, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 24576, "length": 4096, "depth": 1, "zero": true, "data": false},
{ "start": 28672, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 32768},
{ "start": 28672, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 32768, "length": 134184960, "depth": 1, "zero": true, "data": false}]
== spanning two clusters, non-zero before request ==