Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
On 28.06.21 21:10, Eric Blake wrote:
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
Worth mention that the cache will benefit of it?
Oh, right, absolutely. Like so:
"block/io.c's bdrv_co_block_status() will clamp *pnum before returning it to
its caller, but it itself can still make use of the unclamped *pnum value.
Specifically, the block-status cache for protocol nodes will benefit from
storing as large a region as possible."
How about this tweak to the wording to make it flow a little better:
block/io.c's bdrv_co_block_status() will utilize an unclamped *pnum
value for the block-status cache on protocol nodes, prior to clamping
*pnum for return to its caller.
Sure, thanks!
Max
Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
> > > +++ b/include/block/block_int.h
> > > @@ -347,6 +347,11 @@ struct BlockDriver {
> > > * clamped to bdrv_getlength() and aligned to request_alignment,
> > > * as well as non-NULL pnum, map, and file; in turn, the driver
> > > * must return an error or set pnum to an aligned non-zero value.
> > > + *
> > > + * Note that @bytes is just a hint on how big of a region the
> > > + * caller wants to inspect. It is not a limit on *pnum.
> > > + * Implementations are free to return larger values of *pnum if
> > > + * doing so does not incur a performance penalty.
> >
> > Worth mention that the cache will benefit of it?
>
> Oh, right, absolutely. Like so:
>
> "block/io.c's bdrv_co_block_status() will clamp *pnum before returning it to
> its caller, but it itself can still make use of the unclamped *pnum value.
> Specifically, the block-status cache for protocol nodes will benefit from
> storing as large a region as possible."
How about this tweak to the wording to make it flow a little better:
block/io.c's bdrv_co_block_status() will utilize an unclamped *pnum
value for the block-status cache on protocol nodes, prior to clamping
*pnum for return to its caller.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
On 24.06.21 12:25, Vladimir Sementsov-Ogievskiy wrote:
24.06.2021 13:16, Max Reitz wrote:
On 24.06.21 11:15, Vladimir Sementsov-Ogievskiy wrote:
23.06.2021 18:01, Max Reitz wrote:
.bdrv_co_block_status() implementations are free to return a *pnum
that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will
clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for
*pnum.
Suggested-by: Eric Blake
Signed-off-by: Max Reitz
---
include/block/block_int.h | 5 +
1 file changed, 5 insertions(+)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero
value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
Worth mention that the cache will benefit of it?
Oh, right, absolutely. Like so:
"block/io.c's bdrv_co_block_status() will clamp *pnum before
returning it to its caller, but it itself can still make use of the
unclamped *pnum value. Specifically, the block-status cache for
protocol nodes will benefit from storing as large a region as possible."
Sounds good. Do you mean this as an addition or substitution? If the
latter, I'd keep "if doing so does not incur a performance penalty
I meant it as an addition, just a new paragraph.
Max
Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
24.06.2021 13:16, Max Reitz wrote:
On 24.06.21 11:15, Vladimir Sementsov-Ogievskiy wrote:
23.06.2021 18:01, Max Reitz wrote:
.bdrv_co_block_status() implementations are free to return a *pnum that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for *pnum.
Suggested-by: Eric Blake
Signed-off-by: Max Reitz
---
include/block/block_int.h | 5 +
1 file changed, 5 insertions(+)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
Worth mention that the cache will benefit of it?
Oh, right, absolutely. Like so:
"block/io.c's bdrv_co_block_status() will clamp *pnum before returning it to its
caller, but it itself can still make use of the unclamped *pnum value. Specifically, the
block-status cache for protocol nodes will benefit from storing as large a region as
possible."
Sounds good. Do you mean this as an addition or substitution? If the latter, I'd keep
"if doing so does not incur a performance penalty"
--
Best regards,
Vladimir
Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
On 24.06.21 11:15, Vladimir Sementsov-Ogievskiy wrote:
23.06.2021 18:01, Max Reitz wrote:
.bdrv_co_block_status() implementations are free to return a *pnum that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for *pnum.
Suggested-by: Eric Blake
Signed-off-by: Max Reitz
---
include/block/block_int.h | 5 +
1 file changed, 5 insertions(+)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
Worth mention that the cache will benefit of it?
Oh, right, absolutely. Like so:
"block/io.c's bdrv_co_block_status() will clamp *pnum before returning
it to its caller, but it itself can still make use of the unclamped
*pnum value. Specifically, the block-status cache for protocol nodes
will benefit from storing as large a region as possible."
?
Max
Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
23.06.2021 18:01, Max Reitz wrote:
.bdrv_co_block_status() implementations are free to return a *pnum that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for *pnum.
Suggested-by: Eric Blake
Signed-off-by: Max Reitz
---
include/block/block_int.h | 5 +
1 file changed, 5 insertions(+)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
Worth mention that the cache will benefit of it?
Reviewed-by: Vladimir Sementsov-Ogievskiy
*/
int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs,
bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,
--
Best regards,
Vladimir
[PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum
.bdrv_co_block_status() implementations are free to return a *pnum that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for *pnum.
Suggested-by: Eric Blake
Signed-off-by: Max Reitz
---
include/block/block_int.h | 5 +
1 file changed, 5 insertions(+)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ struct BlockDriver {
* clamped to bdrv_getlength() and aligned to request_alignment,
* as well as non-NULL pnum, map, and file; in turn, the driver
* must return an error or set pnum to an aligned non-zero value.
+ *
+ * Note that @bytes is just a hint on how big of a region the
+ * caller wants to inspect. It is not a limit on *pnum.
+ * Implementations are free to return larger values of *pnum if
+ * doing so does not incur a performance penalty.
*/
int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs,
bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,
--
2.31.1
