On 4/28/20 11:29 PM, Eric Blake wrote:
> 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>
> ---
> block/parallels.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/block/parallels.c b/block/parallels.c
> index 2be92cf41708..9dadaa3217b9 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -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);
Reviewed-by: Denis V. Lunev <den@openvz.org>