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qemu-img: avoid unaligned read requests during convert

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in case of large continous areas that share the same allocation status
it happens that the value of s->sector_next_status is unaligned to the
cluster size or even request alignment of the source. Avoid this by
stripping down the s->sector_next_status position to cluster boundaries.

Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <20200901125129.6398-1-pl@kamp.de>
[mreitz: Disable vhdx for 251]
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Peter Lieven 2020-09-01 14:51:29 +02:00 committed by Max Reitz
parent 5eb9a3c7b0
commit af8d43d393
2 changed files with 27 additions and 2 deletions
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22
qemu-img.c
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@ -1666,6 +1666,7 @@ enum ImgConvertBlockStatus {
typedef struct ImgConvertState {
BlockBackend **src;
int64_t *src_sectors;
int *src_alignment;
int src_num;
int64_t total_sectors;
int64_t allocated_sectors;
@ -1732,6 +1733,7 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
if (s->sector_next_status <= sector_num) {
uint64_t offset = (sector_num - src_cur_offset) * BDRV_SECTOR_SIZE;
int64_t count;
int tail;
BlockDriverState *src_bs = blk_bs(s->src[src_cur]);
BlockDriverState *base;
@ -1772,6 +1774,16 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
n = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
/*
* Avoid that s->sector_next_status becomes unaligned to the source
* request alignment and/or cluster size to avoid unnecessary read
* cycles.
*/
tail = (sector_num - src_cur_offset + n) % s->src_alignment[src_cur];
if (n > tail) {
n -= tail;
}
if (ret & BDRV_BLOCK_ZERO) {
s->status = post_backing_zero ? BLK_BACKING_FILE : BLK_ZERO;
} else if (ret & BDRV_BLOCK_DATA) {
@ -2410,8 +2422,10 @@ static int img_convert(int argc, char **argv)
s.src = g_new0(BlockBackend *, s.src_num);
s.src_sectors = g_new(int64_t, s.src_num);
s.src_alignment = g_new(int, s.src_num);
for (bs_i = 0; bs_i < s.src_num; bs_i++) {
BlockDriverState *src_bs;
s.src[bs_i] = img_open(image_opts, argv[optind + bs_i],
fmt, src_flags, src_writethrough, s.quiet,
force_share);
@ -2426,6 +2440,13 @@ static int img_convert(int argc, char **argv)
ret = -1;
goto out;
}
src_bs = blk_bs(s.src[bs_i]);
s.src_alignment[bs_i] = DIV_ROUND_UP(src_bs->bl.request_alignment,
BDRV_SECTOR_SIZE);
if (!bdrv_get_info(src_bs, &bdi)) {
s.src_alignment[bs_i] = MAX(s.src_alignment[bs_i],
bdi.cluster_size / BDRV_SECTOR_SIZE);
}
s.total_sectors += s.src_sectors[bs_i];
}
@ -2708,6 +2729,7 @@ out:
g_free(s.src);
}
g_free(s.src_sectors);
g_free(s.src_alignment);
fail_getopt:
g_free(options);

7
tests/qemu-iotests/251
View File

@ -46,8 +46,11 @@ if [ "$IMGOPTSSYNTAX" = "true" ]; then
# We use json:{} filenames here, so we cannot work with additional options.
_unsupported_fmt $IMGFMT
else
# With VDI, the output is ordered differently. Just disable it.
_unsupported_fmt vdi
# - With VDI, the output is ordered differently. Just disable it.
# - VHDX has large clusters; because qemu-img convert tries to
# align the requests to the cluster size, the output is ordered
# differently, so disable it, too.
_unsupported_fmt vdi vhdx
fi