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parallels: Rework truncation logic

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The parallels driver tries to use truncation for image growth, but can
only do so when reads are guaranteed as zero.  Now that we have a way
to request zero contents from truncation, we can defer the decision to
actual allocation attempts rather than up front, reducing the number
of places that still use bdrv_has_zero_init_truncate.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200428202905.770727-8-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 2020-04-28 15:29:03 -05:00 committed by Kevin Wolf
parent be9c9404db
commit bda4cdcbb9
1 changed files with 16 additions and 9 deletions
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25
block/parallels.c
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@ -166,7 +166,7 @@ static int64_t block_status(BDRVParallelsState *s, int64_t sector_num,
static int64_t allocate_clusters(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, int *pnum)
{
int ret;
int ret = 0;
BDRVParallelsState *s = bs->opaque;
int64_t pos, space, idx, to_allocate, i, len;
@ -196,14 +196,24 @@ static int64_t allocate_clusters(BlockDriverState *bs, int64_t sector_num,
}
if (s->data_end + space > (len >> BDRV_SECTOR_BITS)) {
space += s->prealloc_size;
/*
* We require the expanded size to read back as zero. If the
* user permitted truncation, we try that; but if it fails, we
* force the safer-but-slower fallocate.
*/
if (s->prealloc_mode == PRL_PREALLOC_MODE_TRUNCATE) {
ret = bdrv_truncate(bs->file,
(s->data_end + space) << BDRV_SECTOR_BITS,
false, PREALLOC_MODE_OFF, BDRV_REQ_ZERO_WRITE,
NULL);
if (ret == -ENOTSUP) {
s->prealloc_mode = PRL_PREALLOC_MODE_FALLOCATE;
}
}
if (s->prealloc_mode == PRL_PREALLOC_MODE_FALLOCATE) {
ret = bdrv_pwrite_zeroes(bs->file,
s->data_end << BDRV_SECTOR_BITS,
space << BDRV_SECTOR_BITS, 0);
} else {
ret = bdrv_truncate(bs->file,
(s->data_end + space) << BDRV_SECTOR_BITS,
false, PREALLOC_MODE_OFF, 0, NULL);
}
if (ret < 0) {
return ret;
@ -828,6 +838,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
qemu_opt_get_size_del(opts, PARALLELS_OPT_PREALLOC_SIZE, 0);
s->prealloc_size = MAX(s->tracks, s->prealloc_size >> BDRV_SECTOR_BITS);
buf = qemu_opt_get_del(opts, PARALLELS_OPT_PREALLOC_MODE);
/* prealloc_mode can be downgraded later during allocate_clusters */
s->prealloc_mode = qapi_enum_parse(&prealloc_mode_lookup, buf,
PRL_PREALLOC_MODE_FALLOCATE,
&local_err);
@ -836,10 +847,6 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
goto fail_options;
}
if (!bdrv_has_zero_init_truncate(bs->file->bs)) {
s->prealloc_mode = PRL_PREALLOC_MODE_FALLOCATE;
}
if ((flags & BDRV_O_RDWR) && !(flags & BDRV_O_INACTIVE)) {
s->header->inuse = cpu_to_le32(HEADER_INUSE_MAGIC);
ret = parallels_update_header(bs);