[PATCH] scsi_debug: Make max_sectors configurable

[PATCH] scsi_debug: Make max_sectors configurable

[Bart Van Assche]

Make the SCSI debug host parameter max_sectors configurable to make it
easier to trigger request splitting in the block layer. If this parameter
is not set then the following SCSI core code will set max sectors to 1024:

	if (sht->max_sectors)
		shost->max_sectors = sht->max_sectors;
	else
		shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS;

Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_debug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index aef33d1e346a..101a96530b11 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -913,6 +913,7 @@ static int sdebug_host_max_queue;	/* per host */
 static int sdebug_lowest_aligned = DEF_LOWEST_ALIGNED;
 static int sdebug_max_luns = DEF_MAX_LUNS;
 static int sdebug_max_queue = SDEBUG_CANQUEUE;	/* per submit queue */
+static unsigned int sdebug_max_sectors;
 static unsigned int sdebug_medium_error_start = OPT_MEDIUM_ERR_ADDR;
 static int sdebug_medium_error_count = OPT_MEDIUM_ERR_NUM;
 static int sdebug_ndelay = DEF_NDELAY;	/* if > 0 then unit is nanoseconds */
@@ -7314,6 +7315,7 @@ module_param_named(lowest_aligned, sdebug_lowest_aligned, int, S_IRUGO);
 module_param_named(lun_format, sdebug_lun_am_i, int, S_IRUGO | S_IWUSR);
 module_param_named(max_luns, sdebug_max_luns, int, S_IRUGO | S_IWUSR);
 module_param_named(max_queue, sdebug_max_queue, int, S_IRUGO | S_IWUSR);
+module_param_named(max_sectors, sdebug_max_sectors, uint, 0444);
 module_param_named(medium_error_count, sdebug_medium_error_count, int,
 		   S_IRUGO | S_IWUSR);
 module_param_named(medium_error_start, sdebug_medium_error_start, int,
@@ -7395,6 +7397,7 @@ MODULE_PARM_DESC(lbpws10, "enable LBP, support WRITE SAME(10) with UNMAP bit (de
 MODULE_PARM_DESC(atomic_write, "enable ATOMIC WRITE support, support WRITE ATOMIC(16) (def=0)");
 MODULE_PARM_DESC(lowest_aligned, "lowest aligned lba (def=0)");
 MODULE_PARM_DESC(lun_format, "LUN format: 0->peripheral (def); 1 --> flat address method");
+MODULE_PARM_DESC(max_sectors, "maximum sectors per command");
 MODULE_PARM_DESC(max_luns, "number of LUNs per target to simulate(def=1)");
 MODULE_PARM_DESC(max_queue, "max number of queued commands (1 to max(def))");
 MODULE_PARM_DESC(medium_error_count, "count of sectors to return follow on MEDIUM error");
@@ -9465,6 +9468,7 @@ static int sdebug_driver_probe(struct device *dev)
 	hpnt->cmd_per_lun = sdebug_max_queue;
 	if (!sdebug_clustering)
 		hpnt->dma_boundary = PAGE_SIZE - 1;
+	hpnt->max_sectors = sdebug_max_sectors;
 
 	if (submit_queues > nr_cpu_ids) {
 		pr_warn("%s: trim submit_queues (was %d) to nr_cpu_ids=%u\n",

Re: [PATCH] scsi_debug: Make max_sectors configurable

[John Garry]

On 15/05/2025 18:35, Bart Van Assche wrote:
> Make the SCSI debug host parameter max_sectors configurable to make it
> easier to trigger request splitting in the block layer.

Obviously we can do that via sysfs with the max_sectors file.

Is that really not good enough?

> If this parameter
> is not set then the following SCSI core code will set max sectors to 1024:
> 
> 	if (sht->max_sectors)
> 		shost->max_sectors = sht->max_sectors;
> 	else
> 		shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS;
> 
> Cc: John Garry <john.g.garry@oracle.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   drivers/scsi/scsi_debug.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index aef33d1e346a..101a96530b11 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -913,6 +913,7 @@ static int sdebug_host_max_queue;	/* per host */
>   static int sdebug_lowest_aligned = DEF_LOWEST_ALIGNED;
>   static int sdebug_max_luns = DEF_MAX_LUNS;
>   static int sdebug_max_queue = SDEBUG_CANQUEUE;	/* per submit queue */
> +static unsigned int sdebug_max_sectors;
>   static unsigned int sdebug_medium_error_start = OPT_MEDIUM_ERR_ADDR;
>   static int sdebug_medium_error_count = OPT_MEDIUM_ERR_NUM;
>   static int sdebug_ndelay = DEF_NDELAY;	/* if > 0 then unit is nanoseconds */
> @@ -7314,6 +7315,7 @@ module_param_named(lowest_aligned, sdebug_lowest_aligned, int, S_IRUGO);
>   module_param_named(lun_format, sdebug_lun_am_i, int, S_IRUGO | S_IWUSR);
>   module_param_named(max_luns, sdebug_max_luns, int, S_IRUGO | S_IWUSR);
>   module_param_named(max_queue, sdebug_max_queue, int, S_IRUGO | S_IWUSR);
> +module_param_named(max_sectors, sdebug_max_sectors, uint, 0444);
>   module_param_named(medium_error_count, sdebug_medium_error_count, int,
>   		   S_IRUGO | S_IWUSR);
>   module_param_named(medium_error_start, sdebug_medium_error_start, int,
> @@ -7395,6 +7397,7 @@ MODULE_PARM_DESC(lbpws10, "enable LBP, support WRITE SAME(10) with UNMAP bit (de
>   MODULE_PARM_DESC(atomic_write, "enable ATOMIC WRITE support, support WRITE ATOMIC(16) (def=0)");
>   MODULE_PARM_DESC(lowest_aligned, "lowest aligned lba (def=0)");
>   MODULE_PARM_DESC(lun_format, "LUN format: 0->peripheral (def); 1 --> flat address method");
> +MODULE_PARM_DESC(max_sectors, "maximum sectors per command");
>   MODULE_PARM_DESC(max_luns, "number of LUNs per target to simulate(def=1)");
>   MODULE_PARM_DESC(max_queue, "max number of queued commands (1 to max(def))");
>   MODULE_PARM_DESC(medium_error_count, "count of sectors to return follow on MEDIUM error");
> @@ -9465,6 +9468,7 @@ static int sdebug_driver_probe(struct device *dev)
>   	hpnt->cmd_per_lun = sdebug_max_queue;
>   	if (!sdebug_clustering)
>   		hpnt->dma_boundary = PAGE_SIZE - 1;
> +	hpnt->max_sectors = sdebug_max_sectors;
>   
>   	if (submit_queues > nr_cpu_ids) {
>   		pr_warn("%s: trim submit_queues (was %d) to nr_cpu_ids=%u\n",

Regardless of my view on the merit of this patch, we still have 
max_sectors = -1 in the sht - is that still required?

Thanks,
John

Re: [PATCH] scsi_debug: Make max_sectors configurable

[Bart Van Assche]

On 5/15/25 11:04 AM, John Garry wrote:
> On 15/05/2025 18:35, Bart Van Assche wrote:
>> Make the SCSI debug host parameter max_sectors configurable to make it
>> easier to trigger request splitting in the block layer.
> 
> Obviously we can do that via sysfs with the max_sectors file.

That sounds like a good enough alternative to me. I will look further
into this approach.

Bart.