[PATCH] block: save user max_sectors limit

[PATCH] block: save user max_sectors limit

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

The user can set the max_sectors limit to any valid value via sysfs
/sys/block/<dev>/queue/max_sectors_kb attribute. If the device limits
are ever rescanned, though, the limit reverts back to the kernel defined
BLK_DEF_MAX_SECTORS limit.

Preserve the user's setting for the max_sectors limit as long as it's
valid. The user can reset back to defaults by writing 0 to the sysfs
file.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/blk-settings.c   |  9 +++++++--
 block/blk-sysfs.c      | 10 +++++++++-
 include/linux/blkdev.h |  1 +
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0477c4d527fee..e75304f853bd5 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -40,7 +40,7 @@ void blk_set_default_limits(struct queue_limits *lim)
 	lim->virt_boundary_mask = 0;
 	lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
 	lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
-	lim->max_dev_sectors = 0;
+	lim->max_user_sectors = lim->max_dev_sectors = 0;
 	lim->chunk_sectors = 0;
 	lim->max_write_zeroes_sectors = 0;
 	lim->max_zone_append_sectors = 0;
@@ -135,7 +135,12 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
 	limits->max_hw_sectors = max_hw_sectors;
 
 	max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);
-	max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
+
+	if (limits->max_user_sectors)
+		max_sectors = min_not_zero(max_sectors, limits->max_user_sectors);
+	else
+		max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
+
 	max_sectors = round_down(max_sectors,
 				 limits->logical_block_size >> SECTOR_SHIFT);
 	limits->max_sectors = max_sectors;
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 93d9e9c9a6ea8..db5d1d908f5d9 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -250,8 +250,16 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 	max_hw_sectors_kb = min_not_zero(max_hw_sectors_kb, (unsigned long)
 					 q->limits.max_dev_sectors >> 1);
 
-	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
+	if (max_sectors_kb == 0) {
+		q->limits.max_user_sectors = 0;
+		max_sectors_kb = min_t(unsigned int, max_hw_sectors_kb,
+				       BLK_DEF_MAX_SECTORS >> 1);
+	} else if (max_sectors_kb > max_hw_sectors_kb ||
+		   max_sectors_kb < page_kb)  {
 		return -EINVAL;
+	} else {
+		q->limits.max_user_sectors = max_sectors_kb << 1;
+	}
 
 	spin_lock_irq(&q->queue_lock);
 	q->limits.max_sectors = max_sectors_kb << 1;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 301cf1cf4f2fa..71e97f0a87264 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -288,6 +288,7 @@ struct queue_limits {
 	unsigned int		max_dev_sectors;
 	unsigned int		chunk_sectors;
 	unsigned int		max_sectors;
+	unsigned int		max_user_sectors;
 	unsigned int		max_segment_size;
 	unsigned int		physical_block_size;
 	unsigned int		logical_block_size;
-- 
2.30.2

Re: [PATCH] block: save user max_sectors limit

[Christoph Hellwig]

On Thu, Dec 22, 2022 at 09:52:04AM -0800, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> The user can set the max_sectors limit to any valid value via sysfs
> /sys/block/<dev>/queue/max_sectors_kb attribute. If the device limits
> are ever rescanned, though, the limit reverts back to the kernel defined
> BLK_DEF_MAX_SECTORS limit.
> 
> Preserve the user's setting for the max_sectors limit as long as it's
> valid. The user can reset back to defaults by writing 0 to the sysfs
> file.
> 
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
>  block/blk-settings.c   |  9 +++++++--
>  block/blk-sysfs.c      | 10 +++++++++-
>  include/linux/blkdev.h |  1 +
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 0477c4d527fee..e75304f853bd5 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -40,7 +40,7 @@ void blk_set_default_limits(struct queue_limits *lim)
>  	lim->virt_boundary_mask = 0;
>  	lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
>  	lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
> -	lim->max_dev_sectors = 0;
> +	lim->max_user_sectors = lim->max_dev_sectors = 0;
>  	lim->chunk_sectors = 0;
>  	lim->max_write_zeroes_sectors = 0;
>  	lim->max_zone_append_sectors = 0;
> @@ -135,7 +135,12 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
>  	limits->max_hw_sectors = max_hw_sectors;
>  
>  	max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);
> -	max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
> +
> +	if (limits->max_user_sectors)
> +		max_sectors = min_not_zero(max_sectors, limits->max_user_sectors);

I don't think the min_not_zero here makes sense, as you just checked
max_user_sectors for zero above, and max_sectors better not be zero.

> +	else
> +		max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);

And please make BLK_DEF_MAX_SECTORS an unsigned constant as it should be
and drop the min_t here.  Instead of working around type mismatches
just avoid them from the beginning..

> +	if (max_sectors_kb == 0) {
> +		q->limits.max_user_sectors = 0;
> +		max_sectors_kb = min_t(unsigned int, max_hw_sectors_kb,
> +				       BLK_DEF_MAX_SECTORS >> 1);

.. which will also pay off here.

> +	} else if (max_sectors_kb > max_hw_sectors_kb ||
> +		   max_sectors_kb < page_kb)  {
>  		return -EINVAL;

And this check should probably move above the old one to keep the
sanity checks first.

> +	} else {
> +		q->limits.max_user_sectors = max_sectors_kb << 1;
> +	}

i.e.

	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
		return -EINVAL;

	q->limits.max_user_sectors = max_sectors_kb << 1;

	/* reset to default when the user clears max_sectors_kb: */
	if (max_sectors_kb == 0) {
		max_sectors_kb =
			min(max_hw_sectors_kb, BLK_DEF_MAX_SECTORS >> 1);
	}

Re: [PATCH] block: save user max_sectors limit

[Keith Busch]

On Fri, Dec 23, 2022 at 07:00:09AM +0100, Christoph Hellwig wrote:
> On Thu, Dec 22, 2022 at 09:52:04AM -0800, Keith Busch wrote:
> > +		max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
> 
> And please make BLK_DEF_MAX_SECTORS an unsigned constant as it should be
> and drop the min_t here.  Instead of working around type mismatches
> just avoid them from the beginning..

Let me just make sure I understand: you don't want BLK_DEF_MAX_SECTORS
defined in an enum, and instead want it a 'const unsigned int'? Or
#define?
 
> > +	} else if (max_sectors_kb > max_hw_sectors_kb ||
> > +		   max_sectors_kb < page_kb)  {
> >  		return -EINVAL;
> 
> And this check should probably move above the old one to keep the
> sanity checks first.
> 
> > +	} else {
> > +		q->limits.max_user_sectors = max_sectors_kb << 1;
> > +	}
> 
> i.e.
> 
> 	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
> 		return -EINVAL;
> 
> 	q->limits.max_user_sectors = max_sectors_kb << 1;
> 
> 	/* reset to default when the user clears max_sectors_kb: */
> 	if (max_sectors_kb == 0) {

We'll never reach here since 0 is < page_kb. But I think I can clean
this up a little bit for the next version.

> 		max_sectors_kb =
> 			min(max_hw_sectors_kb, BLK_DEF_MAX_SECTORS >> 1);
> 	}

Re: [PATCH] block: save user max_sectors limit

[Christoph Hellwig]

On Tue, Dec 27, 2022 at 09:49:15AM -0700, Keith Busch wrote:
> > and drop the min_t here.  Instead of working around type mismatches
> > just avoid them from the beginning..
> 
> Let me just make sure I understand: you don't want BLK_DEF_MAX_SECTORS
> defined in an enum, and instead want it a 'const unsigned int'? Or
> #define?

Just make sure it's marked as unsigned, either and enum or define
works, just make sure it has the u suffix.  Note that for enums recent
gccs enforce the same type over different embers, so you might have
to split it from an existing catchall enum into a separate one.

Re: [PATCH] block: save user max_sectors limit

[Damien Le Moal]

On 12/23/22 02:52, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> The user can set the max_sectors limit to any valid value via sysfs
> /sys/block/<dev>/queue/max_sectors_kb attribute. If the device limits
> are ever rescanned, though, the limit reverts back to the kernel defined
> BLK_DEF_MAX_SECTORS limit.
> 
> Preserve the user's setting for the max_sectors limit as long as it's
> valid. The user can reset back to defaults by writing 0 to the sysfs
> file.

Updating Documentation/ABI/stable/sysfs-block about this change would be
nice too.

> 
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
>  block/blk-settings.c   |  9 +++++++--
>  block/blk-sysfs.c      | 10 +++++++++-
>  include/linux/blkdev.h |  1 +
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 0477c4d527fee..e75304f853bd5 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -40,7 +40,7 @@ void blk_set_default_limits(struct queue_limits *lim)
>  	lim->virt_boundary_mask = 0;
>  	lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
>  	lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
> -	lim->max_dev_sectors = 0;
> +	lim->max_user_sectors = lim->max_dev_sectors = 0;
>  	lim->chunk_sectors = 0;
>  	lim->max_write_zeroes_sectors = 0;
>  	lim->max_zone_append_sectors = 0;
> @@ -135,7 +135,12 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
>  	limits->max_hw_sectors = max_hw_sectors;
>  
>  	max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);
> -	max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
> +
> +	if (limits->max_user_sectors)
> +		max_sectors = min_not_zero(max_sectors, limits->max_user_sectors);
> +	else
> +		max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
> +
>  	max_sectors = round_down(max_sectors,
>  				 limits->logical_block_size >> SECTOR_SHIFT);
>  	limits->max_sectors = max_sectors;
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 93d9e9c9a6ea8..db5d1d908f5d9 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -250,8 +250,16 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
>  	max_hw_sectors_kb = min_not_zero(max_hw_sectors_kb, (unsigned long)
>  					 q->limits.max_dev_sectors >> 1);
>  
> -	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
> +	if (max_sectors_kb == 0) {
> +		q->limits.max_user_sectors = 0;
> +		max_sectors_kb = min_t(unsigned int, max_hw_sectors_kb,
> +				       BLK_DEF_MAX_SECTORS >> 1);
> +	} else if (max_sectors_kb > max_hw_sectors_kb ||
> +		   max_sectors_kb < page_kb)  {
>  		return -EINVAL;
> +	} else {
> +		q->limits.max_user_sectors = max_sectors_kb << 1;
> +	}
>  
>  	spin_lock_irq(&q->queue_lock);
>  	q->limits.max_sectors = max_sectors_kb << 1;
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 301cf1cf4f2fa..71e97f0a87264 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -288,6 +288,7 @@ struct queue_limits {
>  	unsigned int		max_dev_sectors;
>  	unsigned int		chunk_sectors;
>  	unsigned int		max_sectors;
> +	unsigned int		max_user_sectors;
>  	unsigned int		max_segment_size;
>  	unsigned int		physical_block_size;
>  	unsigned int		logical_block_size;

-- 
Damien Le Moal
Western Digital Research

[PATCH] block: save user max_sectors limit

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

The user can set the max_sectors limit to any valid value via sysfs
/sys/block/<dev>/queue/max_sectors_kb attribute. If the device limits
are ever rescanned, though, the limit reverts back to the potentially
artificially low BLK_DEF_MAX_SECTORS value.

Preserve the user's setting as long as it's valid and greater than the
default.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/blk-settings.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0477c4d527fee..523348926a800 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -135,7 +135,8 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
 	limits->max_hw_sectors = max_hw_sectors;
 
 	max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);
-	max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);
+	max_sectors = min_t(unsigned int, max_sectors, max(limits->max_sectors,
+							  BLK_DEF_MAX_SECTORS));
 	max_sectors = round_down(max_sectors,
 				 limits->logical_block_size >> SECTOR_SHIFT);
 	limits->max_sectors = max_sectors;
-- 
2.30.2

Re: [PATCH] block: save user max_sectors limit

[Christoph Hellwig]

On Thu, Dec 22, 2022 at 04:32:10PM +0800, kernel test robot wrote:
> >> block/blk-settings.c:138:49: warning: comparison of distinct pointer types ('typeof (limits->max_sectors) *' (aka 'unsigned int *') and 'typeof (BLK_DEF_MAX_SECTORS) *' (aka 'int *')) [-Wcompare-distinct-pointer-types]

Yeah, that's not going to work.  BLK_DEF_MAX_SECTORS should probably
become an unsigned constant to fix this.

Re: [PATCH] block: save user max_sectors limit

[Keith Busch]

On Thu, Dec 22, 2022 at 09:40:11AM +0100, Christoph Hellwig wrote:
> On Thu, Dec 22, 2022 at 04:32:10PM +0800, kernel test robot wrote:
> > >> block/blk-settings.c:138:49: warning: comparison of distinct pointer types ('typeof (limits->max_sectors) *' (aka 'unsigned int *') and 'typeof (BLK_DEF_MAX_SECTORS) *' (aka 'int *')) [-Wcompare-distinct-pointer-types]
> 
> Yeah, that's not going to work.  BLK_DEF_MAX_SECTORS should probably
> become an unsigned constant to fix this.

Hm, I should have used max_t() instead of max().

But thinking on this again, we probably want to respect the user setting
even if it's lower than the default too, not just if its larger. I
believe that will require a new queue limit to save that value.

Re: [PATCH] block: save user max_sectors limit

[Martin K. Petersen]

Keith,

> But thinking on this again, we probably want to respect the user
> setting even if it's lower than the default too, not just if its
> larger. I believe that will require a new queue limit to save that
> value.

Yeah, I have struggled with the same problem for various user parameter
overrides in SCSI. Lowering defaults or detected values is fairly
common.

-- 
Martin K. Petersen	Oracle Linux Engineering