From: Nitesh Shetty <nj.shetty@samsung.com>

Add device limits as sysfs entries,
        - copy_offload (RW)
        - copy_max_bytes (RW)
        - copy_max_bytes_hw (RO)

Above limits help to split the copy payload in block layer.
copy_offload: used for setting copy offload(1) or emulation(0).
copy_max_bytes: maximum total length of copy in single payload.
copy_max_bytes_hw: Reflects the device supported maximum limit.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 Documentation/ABI/stable/sysfs-block | 36 ++++++++++++++++
 block/blk-settings.c                 | 24 +++++++++++
 block/blk-sysfs.c                    | 64 ++++++++++++++++++++++++++++
 include/linux/blkdev.h               | 12 ++++++
 include/uapi/linux/fs.h              |  3 ++
 5 files changed, 139 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index c57e5b7cb532..f5c56ad91ad6 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -155,6 +155,42 @@ Description:
 		last zone of the device which may be smaller.
 
 
+What:		/sys/block/<disk>/queue/copy_offload
+Date:		November 2022
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] When read, this file shows whether offloading copy to
+		device is enabled (1) or disabled (0). Writing '0' to this
+		file will disable offloading copies for this device.
+		Writing any '1' value will enable this feature. If device
+		does not support offloading, then writing 1, will result in
+		error.
+
+
+What:		/sys/block/<disk>/queue/copy_max_bytes
+Date:		November 2022
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
+		device, 'copy_max_bytes' setting is the software limit.
+		Setting this value lower will make Linux issue smaller size
+		copies from block layer.
+
+
+What:		/sys/block/<disk>/queue/copy_max_bytes_hw
+Date:		November 2022
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] Devices that support offloading copy functionality may have
+		internal limits on the number of bytes that can be offloaded
+		in a single operation. The `copy_max_bytes_hw`
+		parameter is set by the device driver to the maximum number of
+		bytes that can be copied in a single operation. Copy
+		requests issued to the device must not exceed this limit.
+		A value of 0 means that the device does not
+		support copy offload.
+
+
 What:		/sys/block/<disk>/queue/crypto/
 Date:		February 2022
 Contact:	linux-block@vger.kernel.org
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 896b4654ab00..350f3584f691 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -59,6 +59,8 @@ void blk_set_default_limits(struct queue_limits *lim)
 	lim->zoned = BLK_ZONED_NONE;
 	lim->zone_write_granularity = 0;
 	lim->dma_alignment = 511;
+	lim->max_copy_sectors_hw = 0;
+	lim->max_copy_sectors = 0;
 }
 
 /**
@@ -82,6 +84,8 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 	lim->max_dev_sectors = UINT_MAX;
 	lim->max_write_zeroes_sectors = UINT_MAX;
 	lim->max_zone_append_sectors = UINT_MAX;
+	lim->max_copy_sectors_hw = ULONG_MAX;
+	lim->max_copy_sectors = ULONG_MAX;
 }
 EXPORT_SYMBOL(blk_set_stacking_limits);
 
@@ -183,6 +187,22 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
 }
 EXPORT_SYMBOL(blk_queue_max_discard_sectors);
 
+/**
+ * blk_queue_max_copy_sectors_hw - set max sectors for a single copy payload
+ * @q:  the request queue for the device
+ * @max_copy_sectors: maximum number of sectors to copy
+ **/
+void blk_queue_max_copy_sectors_hw(struct request_queue *q,
+		unsigned int max_copy_sectors)
+{
+	if (max_copy_sectors >= MAX_COPY_TOTAL_LENGTH)
+		max_copy_sectors = MAX_COPY_TOTAL_LENGTH;
+
+	q->limits.max_copy_sectors_hw = max_copy_sectors;
+	q->limits.max_copy_sectors = max_copy_sectors;
+}
+EXPORT_SYMBOL_GPL(blk_queue_max_copy_sectors_hw);
+
 /**
  * blk_queue_max_secure_erase_sectors - set max sectors for a secure erase
  * @q:  the request queue for the device
@@ -578,6 +598,10 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	t->max_segment_size = min_not_zero(t->max_segment_size,
 					   b->max_segment_size);
 
+	t->max_copy_sectors = min(t->max_copy_sectors, b->max_copy_sectors);
+	t->max_copy_sectors_hw = min(t->max_copy_sectors_hw,
+						b->max_copy_sectors_hw);
+
 	t->misaligned |= b->misaligned;
 
 	alignment = queue_limit_alignment_offset(b, start);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 1a743b4f2958..dccb162cf318 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -213,6 +213,63 @@ static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *pag
 	return queue_var_show(0, page);
 }
 
+static ssize_t queue_copy_offload_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(blk_queue_copy(q), page);
+}
+
+static ssize_t queue_copy_offload_store(struct request_queue *q,
+				       const char *page, size_t count)
+{
+	s64 copy_offload;
+	ssize_t ret = queue_var_store64(&copy_offload, page);
+
+	if (ret < 0)
+		return ret;
+
+	if (copy_offload && !q->limits.max_copy_sectors_hw)
+		return -EINVAL;
+
+	if (copy_offload)
+		blk_queue_flag_set(QUEUE_FLAG_COPY, q);
+	else
+		blk_queue_flag_clear(QUEUE_FLAG_COPY, q);
+
+	return count;
+}
+
+static ssize_t queue_copy_max_hw_show(struct request_queue *q, char *page)
+{
+	return sprintf(page, "%llu\n", (unsigned long long)
+			q->limits.max_copy_sectors_hw << SECTOR_SHIFT);
+}
+
+static ssize_t queue_copy_max_show(struct request_queue *q, char *page)
+{
+	return sprintf(page, "%llu\n", (unsigned long long)
+			q->limits.max_copy_sectors << SECTOR_SHIFT);
+}
+
+static ssize_t queue_copy_max_store(struct request_queue *q,
+				       const char *page, size_t count)
+{
+	s64 max_copy;
+	ssize_t ret = queue_var_store64(&max_copy, page);
+
+	if (ret < 0)
+		return ret;
+
+	if (max_copy & (queue_logical_block_size(q) - 1))
+		return -EINVAL;
+
+	max_copy >>= SECTOR_SHIFT;
+	if (max_copy > q->limits.max_copy_sectors_hw)
+		max_copy = q->limits.max_copy_sectors_hw;
+
+	q->limits.max_copy_sectors = max_copy;
+	return count;
+}
+
 static ssize_t queue_write_same_max_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(0, page);
@@ -591,6 +648,10 @@ QUEUE_RO_ENTRY(queue_nr_zones, "nr_zones");
 QUEUE_RO_ENTRY(queue_max_open_zones, "max_open_zones");
 QUEUE_RO_ENTRY(queue_max_active_zones, "max_active_zones");
 
+QUEUE_RW_ENTRY(queue_copy_offload, "copy_offload");
+QUEUE_RO_ENTRY(queue_copy_max_hw, "copy_max_bytes_hw");
+QUEUE_RW_ENTRY(queue_copy_max, "copy_max_bytes");
+
 QUEUE_RW_ENTRY(queue_nomerges, "nomerges");
 QUEUE_RW_ENTRY(queue_rq_affinity, "rq_affinity");
 QUEUE_RW_ENTRY(queue_poll, "io_poll");
@@ -638,6 +699,9 @@ static struct attribute *queue_attrs[] = {
 	&queue_discard_max_entry.attr,
 	&queue_discard_max_hw_entry.attr,
 	&queue_discard_zeroes_data_entry.attr,
+	&queue_copy_offload_entry.attr,
+	&queue_copy_max_hw_entry.attr,
+	&queue_copy_max_entry.attr,
 	&queue_write_same_max_entry.attr,
 	&queue_write_zeroes_max_entry.attr,
 	&queue_zone_append_max_entry.attr,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e3242e67a8e3..200338f2ec2e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -298,6 +298,9 @@ struct queue_limits {
 	unsigned int		discard_alignment;
 	unsigned int		zone_write_granularity;
 
+	unsigned long		max_copy_sectors_hw;
+	unsigned long		max_copy_sectors;
+
 	unsigned short		max_segments;
 	unsigned short		max_integrity_segments;
 	unsigned short		max_discard_segments;
@@ -564,6 +567,7 @@ struct request_queue {
 #define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */
 #define QUEUE_FLAG_SQ_SCHED     30	/* single queue style io dispatch */
 #define QUEUE_FLAG_SKIP_TAGSET_QUIESCE	31 /* quiesce_tagset skip the queue*/
+#define QUEUE_FLAG_COPY		32	/* supports copy offload */
 
 #define QUEUE_FLAG_MQ_DEFAULT	((1UL << QUEUE_FLAG_IO_STAT) |		\
 				 (1UL << QUEUE_FLAG_SAME_COMP) |	\
@@ -584,6 +588,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 	test_bit(QUEUE_FLAG_STABLE_WRITES, &(q)->queue_flags)
 #define blk_queue_io_stat(q)	test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
 #define blk_queue_add_random(q)	test_bit(QUEUE_FLAG_ADD_RANDOM, &(q)->queue_flags)
+#define blk_queue_copy(q)	test_bit(QUEUE_FLAG_COPY, &(q)->queue_flags)
 #define blk_queue_zone_resetall(q)	\
 	test_bit(QUEUE_FLAG_ZONE_RESETALL, &(q)->queue_flags)
 #define blk_queue_dax(q)	test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
@@ -902,6 +907,8 @@ extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_max_segments(struct request_queue *, unsigned short);
 extern void blk_queue_max_discard_segments(struct request_queue *,
 		unsigned short);
+extern void blk_queue_max_copy_sectors_hw(struct request_queue *q,
+		unsigned int max_copy_sectors);
 void blk_queue_max_secure_erase_sectors(struct request_queue *q,
 		unsigned int max_sectors);
 extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
@@ -1221,6 +1228,11 @@ static inline unsigned int bdev_discard_granularity(struct block_device *bdev)
 	return bdev_get_queue(bdev)->limits.discard_granularity;
 }
 
+static inline unsigned int bdev_max_copy_sectors(struct block_device *bdev)
+{
+	return bdev_get_queue(bdev)->limits.max_copy_sectors;
+}
+
 static inline unsigned int
 bdev_max_secure_erase_sectors(struct block_device *bdev)
 {
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7b56871029c..b3ad173f619c 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -64,6 +64,9 @@ struct fstrim_range {
 	__u64 minlen;
 };
 
+/* maximum total copy length */
+#define MAX_COPY_TOTAL_LENGTH	(1 << 27)
+
 /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
 #define FILE_DEDUPE_RANGE_SAME		0
 #define FILE_DEDUPE_RANGE_DIFFERS	1
-- 
2.35.1.500.gb896f729e2

On 3/27/23 17:40, Anuj Gupta wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
> 
> Add device limits as sysfs entries,
>         - copy_offload (RW)
>         - copy_max_bytes (RW)
>         - copy_max_bytes_hw (RO)
> 
> Above limits help to split the copy payload in block layer.
> copy_offload: used for setting copy offload(1) or emulation(0).
> copy_max_bytes: maximum total length of copy in single payload.
> copy_max_bytes_hw: Reflects the device supported maximum limit.
> 
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> ---
>  Documentation/ABI/stable/sysfs-block | 36 ++++++++++++++++
>  block/blk-settings.c                 | 24 +++++++++++
>  block/blk-sysfs.c                    | 64 ++++++++++++++++++++++++++++
>  include/linux/blkdev.h               | 12 ++++++
>  include/uapi/linux/fs.h              |  3 ++
>  5 files changed, 139 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
> index c57e5b7cb532..f5c56ad91ad6 100644
> --- a/Documentation/ABI/stable/sysfs-block
> +++ b/Documentation/ABI/stable/sysfs-block
> @@ -155,6 +155,42 @@ Description:
>  		last zone of the device which may be smaller.
>  
>  
> +What:		/sys/block/<disk>/queue/copy_offload
> +Date:		November 2022
> +Contact:	linux-block@vger.kernel.org
> +Description:
> +		[RW] When read, this file shows whether offloading copy to
> +		device is enabled (1) or disabled (0). Writing '0' to this

...to a device...

> +		file will disable offloading copies for this device.
> +		Writing any '1' value will enable this feature. If device

If the device does...

> +		does not support offloading, then writing 1, will result in
> +		error.
> +
> +
> +What:		/sys/block/<disk>/queue/copy_max_bytes
> +Date:		November 2022
> +Contact:	linux-block@vger.kernel.org
> +Description:
> +		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
> +		device, 'copy_max_bytes' setting is the software limit.
> +		Setting this value lower will make Linux issue smaller size
> +		copies from block layer.

		This is the maximum number of bytes that the block
                layer will allow for a copy request. Must be smaller than
                or equal to the maximum size allowed by the hardware indicated
		by copy_max_bytes_hw. Write 0 to use the default kernel
		settings.

> +
> +
> +What:		/sys/block/<disk>/queue/copy_max_bytes_hw
> +Date:		November 2022
> +Contact:	linux-block@vger.kernel.org
> +Description:
> +		[RO] Devices that support offloading copy functionality may have
> +		internal limits on the number of bytes that can be offloaded
> +		in a single operation. The `copy_max_bytes_hw`
> +		parameter is set by the device driver to the maximum number of
> +		bytes that can be copied in a single operation. Copy
> +		requests issued to the device must not exceed this limit.
> +		A value of 0 means that the device does not
> +		support copy offload.

		[RO] This is the maximum number of kilobytes supported in a
                single data copy offload operation. A value of 0 means that the
		device does not support copy offload.

> +
> +
>  What:		/sys/block/<disk>/queue/crypto/
>  Date:		February 2022
>  Contact:	linux-block@vger.kernel.org
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 896b4654ab00..350f3584f691 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -59,6 +59,8 @@ void blk_set_default_limits(struct queue_limits *lim)
>  	lim->zoned = BLK_ZONED_NONE;
>  	lim->zone_write_granularity = 0;
>  	lim->dma_alignment = 511;
> +	lim->max_copy_sectors_hw = 0;
> +	lim->max_copy_sectors = 0;
>  }
>  
>  /**
> @@ -82,6 +84,8 @@ void blk_set_stacking_limits(struct queue_limits *lim)
>  	lim->max_dev_sectors = UINT_MAX;
>  	lim->max_write_zeroes_sectors = UINT_MAX;
>  	lim->max_zone_append_sectors = UINT_MAX;
> +	lim->max_copy_sectors_hw = ULONG_MAX;
> +	lim->max_copy_sectors = ULONG_MAX;
>  }
>  EXPORT_SYMBOL(blk_set_stacking_limits);
>  
> @@ -183,6 +187,22 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
>  }
>  EXPORT_SYMBOL(blk_queue_max_discard_sectors);
>  
> +/**
> + * blk_queue_max_copy_sectors_hw - set max sectors for a single copy payload
> + * @q:  the request queue for the device
> + * @max_copy_sectors: maximum number of sectors to copy
> + **/
> +void blk_queue_max_copy_sectors_hw(struct request_queue *q,
> +		unsigned int max_copy_sectors)
> +{
> +	if (max_copy_sectors >= MAX_COPY_TOTAL_LENGTH)

Confusing name as LENGTH may be interpreted as bytes. MAX_COPY_SECTORS would be
better.

> +		max_copy_sectors = MAX_COPY_TOTAL_LENGTH;
> +
> +	q->limits.max_copy_sectors_hw = max_copy_sectors;
> +	q->limits.max_copy_sectors = max_copy_sectors;
> +}
> +EXPORT_SYMBOL_GPL(blk_queue_max_copy_sectors_hw);


-- 
Damien Le Moal
Western Digital Research

On Wed, Mar 29, 2023 at 05:40:09PM +0900, Damien Le Moal wrote:
> On 3/27/23 17:40, Anuj Gupta wrote:
> > From: Nitesh Shetty <nj.shetty@samsung.com>
> > 
> > Add device limits as sysfs entries,
> >         - copy_offload (RW)
> >         - copy_max_bytes (RW)
> >         - copy_max_bytes_hw (RO)
> > 
> > Above limits help to split the copy payload in block layer.
> > copy_offload: used for setting copy offload(1) or emulation(0).
> > copy_max_bytes: maximum total length of copy in single payload.
> > copy_max_bytes_hw: Reflects the device supported maximum limit.
> > 
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
> > Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> > Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> > Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> > ---
> >  Documentation/ABI/stable/sysfs-block | 36 ++++++++++++++++
> >  block/blk-settings.c                 | 24 +++++++++++
> >  block/blk-sysfs.c                    | 64 ++++++++++++++++++++++++++++
> >  include/linux/blkdev.h               | 12 ++++++
> >  include/uapi/linux/fs.h              |  3 ++
> >  5 files changed, 139 insertions(+)
> > 
> > diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
> > index c57e5b7cb532..f5c56ad91ad6 100644
> > --- a/Documentation/ABI/stable/sysfs-block
> > +++ b/Documentation/ABI/stable/sysfs-block
> > @@ -155,6 +155,42 @@ Description:
> >  		last zone of the device which may be smaller.
> >  
> >  
> > +What:		/sys/block/<disk>/queue/copy_offload
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RW] When read, this file shows whether offloading copy to
> > +		device is enabled (1) or disabled (0). Writing '0' to this
> 
> ...to a device...
> 
acked

> > +		file will disable offloading copies for this device.
> > +		Writing any '1' value will enable this feature. If device
> 
> If the device does...
> 
acked

> > +		does not support offloading, then writing 1, will result in
> > +		error.
> > +
> > +
> > +What:		/sys/block/<disk>/queue/copy_max_bytes
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
> > +		device, 'copy_max_bytes' setting is the software limit.
> > +		Setting this value lower will make Linux issue smaller size
> > +		copies from block layer.
> 
> 		This is the maximum number of bytes that the block
>                 layer will allow for a copy request. Must be smaller than
>                 or equal to the maximum size allowed by the hardware indicated

Looks good.  Will update in next version. We took reference from discard. 

> 		by copy_max_bytes_hw. Write 0 to use the default kernel
> 		settings.
> 

Nack, writing 0 will not set it to default value. (default value is
copy_max_bytes = copy_max_bytes_hw)

> > +
> > +
> > +What:		/sys/block/<disk>/queue/copy_max_bytes_hw
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RO] Devices that support offloading copy functionality may have
> > +		internal limits on the number of bytes that can be offloaded
> > +		in a single operation. The `copy_max_bytes_hw`
> > +		parameter is set by the device driver to the maximum number of
> > +		bytes that can be copied in a single operation. Copy
> > +		requests issued to the device must not exceed this limit.
> > +		A value of 0 means that the device does not
> > +		support copy offload.
> 
> 		[RO] This is the maximum number of kilobytes supported in a
>                 single data copy offload operation. A value of 0 means that the
> 		device does not support copy offload.
> 

Nack, value is in bytes. Same as discard.

> > +
> > +
> >  What:		/sys/block/<disk>/queue/crypto/
> >  Date:		February 2022
> >  Contact:	linux-block@vger.kernel.org
> > diff --git a/block/blk-settings.c b/block/blk-settings.c
> > index 896b4654ab00..350f3584f691 100644
> > --- a/block/blk-settings.c
> > +++ b/block/blk-settings.c
> > @@ -59,6 +59,8 @@ void blk_set_default_limits(struct queue_limits *lim)
> >  	lim->zoned = BLK_ZONED_NONE;
> >  	lim->zone_write_granularity = 0;
> >  	lim->dma_alignment = 511;
> > +	lim->max_copy_sectors_hw = 0;
> > +	lim->max_copy_sectors = 0;
> >  }
> >  
> >  /**
> > @@ -82,6 +84,8 @@ void blk_set_stacking_limits(struct queue_limits *lim)
> >  	lim->max_dev_sectors = UINT_MAX;
> >  	lim->max_write_zeroes_sectors = UINT_MAX;
> >  	lim->max_zone_append_sectors = UINT_MAX;
> > +	lim->max_copy_sectors_hw = ULONG_MAX;
> > +	lim->max_copy_sectors = ULONG_MAX;
> >  }
> >  EXPORT_SYMBOL(blk_set_stacking_limits);
> >  
> > @@ -183,6 +187,22 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
> >  }
> >  EXPORT_SYMBOL(blk_queue_max_discard_sectors);
> >  
> > +/**
> > + * blk_queue_max_copy_sectors_hw - set max sectors for a single copy payload
> > + * @q:  the request queue for the device
> > + * @max_copy_sectors: maximum number of sectors to copy
> > + **/
> > +void blk_queue_max_copy_sectors_hw(struct request_queue *q,
> > +		unsigned int max_copy_sectors)
> > +{
> > +	if (max_copy_sectors >= MAX_COPY_TOTAL_LENGTH)
> 
> Confusing name as LENGTH may be interpreted as bytes. MAX_COPY_SECTORS would be
> better.
> 

Agreed, we will make MAX_COPY_TOTAL_LENGTH explicit to bytes.
We also check this limit against user payload length which is in bytes(patch 2).
So there is a inconsistency from our end (patch 1 and 2). We will fix this
in next version.

> > +		max_copy_sectors = MAX_COPY_TOTAL_LENGTH;
> > +
> > +	q->limits.max_copy_sectors_hw = max_copy_sectors;
> > +	q->limits.max_copy_sectors = max_copy_sectors;
> > +}
> > +EXPORT_SYMBOL_GPL(blk_queue_max_copy_sectors_hw);
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research
> 
> 

On 3/29/23 19:41, Nitesh Shetty wrote:
>>> +What:		/sys/block/<disk>/queue/copy_max_bytes
>>> +Date:		November 2022
>>> +Contact:	linux-block@vger.kernel.org
>>> +Description:
>>> +		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
>>> +		device, 'copy_max_bytes' setting is the software limit.
>>> +		Setting this value lower will make Linux issue smaller size
>>> +		copies from block layer.
>>
>> 		This is the maximum number of bytes that the block
>>                 layer will allow for a copy request. Must be smaller than
>>                 or equal to the maximum size allowed by the hardware indicated
> 
> Looks good.  Will update in next version. We took reference from discard. 
> 
>> 		by copy_max_bytes_hw. Write 0 to use the default kernel
>> 		settings.
>>
> 
> Nack, writing 0 will not set it to default value. (default value is
> copy_max_bytes = copy_max_bytes_hw)

It is trivial to make it work that way, which would match how max_sectors_kb
works. Write 0 to return copy_max_bytes being equal to the default
copy_max_bytes_hw.

The other possibility that is also interesting is "write 0 to disable copy
offload and use emulation". This one may actually be more useful.

> 
>>> +
>>> +
>>> +What:		/sys/block/<disk>/queue/copy_max_bytes_hw
>>> +Date:		November 2022
>>> +Contact:	linux-block@vger.kernel.org
>>> +Description:
>>> +		[RO] Devices that support offloading copy functionality may have
>>> +		internal limits on the number of bytes that can be offloaded
>>> +		in a single operation. The `copy_max_bytes_hw`
>>> +		parameter is set by the device driver to the maximum number of
>>> +		bytes that can be copied in a single operation. Copy
>>> +		requests issued to the device must not exceed this limit.
>>> +		A value of 0 means that the device does not
>>> +		support copy offload.
>>
>> 		[RO] This is the maximum number of kilobytes supported in a
>>                 single data copy offload operation. A value of 0 means that the
>> 		device does not support copy offload.
>>
> 
> Nack, value is in bytes. Same as discard.

Typo. I meant Bytes. Your text is too long an too convoluted, so unclear.

-- 
Damien Le Moal
Western Digital Research

On Wed, Mar 29, 2023 at 09:24:11PM +0900, Damien Le Moal wrote:
> On 3/29/23 19:41, Nitesh Shetty wrote:
> >>> +What:		/sys/block/<disk>/queue/copy_max_bytes
> >>> +Date:		November 2022
> >>> +Contact:	linux-block@vger.kernel.org
> >>> +Description:
> >>> +		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
> >>> +		device, 'copy_max_bytes' setting is the software limit.
> >>> +		Setting this value lower will make Linux issue smaller size
> >>> +		copies from block layer.
> >>
> >> 		This is the maximum number of bytes that the block
> >>                 layer will allow for a copy request. Must be smaller than
> >>                 or equal to the maximum size allowed by the hardware indicated
> > 
> > Looks good.  Will update in next version. We took reference from discard. 
> > 
> >> 		by copy_max_bytes_hw. Write 0 to use the default kernel
> >> 		settings.
> >>
> > 
> > Nack, writing 0 will not set it to default value. (default value is
> > copy_max_bytes = copy_max_bytes_hw)
> 
> It is trivial to make it work that way, which would match how max_sectors_kb
> works. Write 0 to return copy_max_bytes being equal to the default
> copy_max_bytes_hw.
>
> The other possibility that is also interesting is "write 0 to disable copy
> offload and use emulation". This one may actually be more useful.
>

We were following discard implementation.
I feel now both options are good. We can finalize based on community feedback.

> > 
> >>> +
> >>> +
> >>> +What:		/sys/block/<disk>/queue/copy_max_bytes_hw
> >>> +Date:		November 2022
> >>> +Contact:	linux-block@vger.kernel.org
> >>> +Description:
> >>> +		[RO] Devices that support offloading copy functionality may have
> >>> +		internal limits on the number of bytes that can be offloaded
> >>> +		in a single operation. The `copy_max_bytes_hw`
> >>> +		parameter is set by the device driver to the maximum number of
> >>> +		bytes that can be copied in a single operation. Copy
> >>> +		requests issued to the device must not exceed this limit.
> >>> +		A value of 0 means that the device does not
> >>> +		support copy offload.
> >>
> >> 		[RO] This is the maximum number of kilobytes supported in a
> >>                 single data copy offload operation. A value of 0 means that the
> >> 		device does not support copy offload.
> >>
> > 
> > Nack, value is in bytes. Same as discard.
> 
> Typo. I meant Bytes. Your text is too long an too convoluted, so unclear.
>
Acked, will update in next version

> -- 
> Damien Le Moal
> Western Digital Research
> 
>