block/backup-top.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-)
backup-top "supports" write-unchanged, by skipping CBW operation in
backup_top_co_pwritev. But it forgets to do the same in
backup_top_co_pwrite_zeroes, as well as declare support for
BDRV_REQ_WRITE_UNCHANGED.
Fix this, and, while being here, declare also support for flags
supported by source child.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
block/backup-top.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/block/backup-top.c b/block/backup-top.c
index 9aed2eb4c0..0e28fecc21 100644
--- a/block/backup-top.c
+++ b/block/backup-top.c
@@ -48,11 +48,17 @@ static coroutine_fn int backup_top_co_preadv(
}
static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
- uint64_t bytes)
+ uint64_t bytes, BdrvRequestFlags flags)
{
BDRVBackupTopState *s = bs->opaque;
- uint64_t end = QEMU_ALIGN_UP(offset + bytes, s->bcs->cluster_size);
- uint64_t off = QEMU_ALIGN_DOWN(offset, s->bcs->cluster_size);
+ uint64_t off, end;
+
+ if (flags & BDRV_REQ_WRITE_UNCHANGED) {
+ return 0;
+ }
+
+ off = QEMU_ALIGN_DOWN(offset, s->bcs->cluster_size);
+ end = QEMU_ALIGN_UP(offset + bytes, s->bcs->cluster_size);
return block_copy(s->bcs, off, end - off, NULL);
}
@@ -60,7 +66,7 @@ static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
static int coroutine_fn backup_top_co_pdiscard(BlockDriverState *bs,
int64_t offset, int bytes)
{
- int ret = backup_top_cbw(bs, offset, bytes);
+ int ret = backup_top_cbw(bs, offset, bytes, 0);
if (ret < 0) {
return ret;
}
@@ -71,7 +77,7 @@ static int coroutine_fn backup_top_co_pdiscard(BlockDriverState *bs,
static int coroutine_fn backup_top_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int bytes, BdrvRequestFlags flags)
{
- int ret = backup_top_cbw(bs, offset, bytes);
+ int ret = backup_top_cbw(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
@@ -84,11 +90,9 @@ static coroutine_fn int backup_top_co_pwritev(BlockDriverState *bs,
uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
- if (!(flags & BDRV_REQ_WRITE_UNCHANGED)) {
- int ret = backup_top_cbw(bs, offset, bytes);
- if (ret < 0) {
- return ret;
- }
+ int ret = backup_top_cbw(bs, offset, bytes, flags);
+ if (ret < 0) {
+ return ret;
}
return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
@@ -197,6 +201,10 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
top->total_sectors = source->total_sectors;
state = top->opaque;
+ top->supported_write_flags =
+ BDRV_REQ_WRITE_UNCHANGED | source->supported_write_flags;
+ top->supported_zero_flags =
+ BDRV_REQ_WRITE_UNCHANGED | source->supported_zero_flags;
bdrv_ref(target);
state->target = bdrv_attach_child(top, target, "target", &child_file, errp);
--
2.21.0
On 1/31/20 12:48 PM, Vladimir Sementsov-Ogievskiy wrote:
> backup-top "supports" write-unchanged, by skipping CBW operation in
> backup_top_co_pwritev. But it forgets to do the same in
> backup_top_co_pwrite_zeroes, as well as declare support for
> BDRV_REQ_WRITE_UNCHANGED.
>
> Fix this, and, while being here, declare also support for flags
> supported by source child.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> block/backup-top.c | 28 ++++++++++++++++++----------
> 1 file changed, 18 insertions(+), 10 deletions(-)
> @@ -197,6 +201,10 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
>
> top->total_sectors = source->total_sectors;
> state = top->opaque;
> + top->supported_write_flags =
> + BDRV_REQ_WRITE_UNCHANGED | source->supported_write_flags;
> + top->supported_zero_flags =
> + BDRV_REQ_WRITE_UNCHANGED | source->supported_zero_flags;
Elsewhere, in block/filter-compress.c we do:
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
bs->file->bs->supported_zero_flags);
That's slightly more robust (if the block layer adds new BDRV_REQ_ bits,
we don't have to revisit filter-compress.c to decide if blindly exposing
those bits breaks for some reason, but rahter DO have to amend the line
to opt-in to supporting the new bits). Whereas your code does NOT need
editing if passing on the new bit is safe, but risks a subtle breakage
if we forget to filter out the new bit when passing it on would be
unsafe. I tend to lean towards safety and opt-in over blind
pass-through that works with the current set of defined bits, but not
enough to withhold:
Reviewed-by: Eric Blake <eblake@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
31.01.2020 22:38, Eric Blake wrote: > On 1/31/20 12:48 PM, Vladimir Sementsov-Ogievskiy wrote: >> backup-top "supports" write-unchanged, by skipping CBW operation in >> backup_top_co_pwritev. But it forgets to do the same in >> backup_top_co_pwrite_zeroes, as well as declare support for >> BDRV_REQ_WRITE_UNCHANGED. >> >> Fix this, and, while being here, declare also support for flags >> supported by source child. >> >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> >> --- >> block/backup-top.c | 28 ++++++++++++++++++---------- >> 1 file changed, 18 insertions(+), 10 deletions(-) > > >> @@ -197,6 +201,10 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source, >> top->total_sectors = source->total_sectors; >> state = top->opaque; >> + top->supported_write_flags = >> + BDRV_REQ_WRITE_UNCHANGED | source->supported_write_flags; >> + top->supported_zero_flags = >> + BDRV_REQ_WRITE_UNCHANGED | source->supported_zero_flags; > > Elsewhere, in block/filter-compress.c we do: > > bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED | > (BDRV_REQ_FUA & bs->file->bs->supported_write_flags); > > bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED | > ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) & > bs->file->bs->supported_zero_flags); > I've looked at this too, but didn't understand, why we need it. Now with your description, I see that this make sense. I'll resend with same pattern, thanks. > That's slightly more robust (if the block layer adds new BDRV_REQ_ bits, we don't have to revisit filter-compress.c to decide if blindly exposing those bits breaks for some reason, but rahter DO have to amend the line to opt-in to supporting the new bits). Whereas your code does NOT need editing if passing on the new bit is safe, but risks a subtle breakage if we forget to filter out the new bit when passing it on would be unsafe. I tend to lean towards safety and opt-in over blind pass-through that works with the current set of defined bits, but not enough to withhold: > > Reviewed-by: Eric Blake <eblake@redhat.com> > -- Best regards, Vladimir
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