Re: [PATCH v3 6/6] scsi_debug: Support configuring the maximum segment size

[John Garry <john.g.garry@oracle.com>]

>   drivers/scsi/scsi_debug.c | 26 +++++++++++++++++++++++++-
>   1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 1515495fd9ea..7e5e171bfcda 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -915,6 +915,7 @@ 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_segment_size = UINT_MAX;
>   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 */
> @@ -1041,6 +1042,26 @@ static const int condition_met_result = SAM_STAT_CONDITION_MET;
>   static struct dentry *sdebug_debugfs_root;
>   static ASYNC_DOMAIN_EXCLUSIVE(sdebug_async_domain);
>   
> +static int sdebug_set_max_segment_size(const char *val,
> +				       const struct kernel_param *kp)

I don't know why you just don't have code in sdebug_driver_probe() like 
the following instead:

hpnt->max_segment_size = max(sdebug_max_segment_size, BLK_MIN_SEGMENT_SIZE);


> +{
> +	int res;
> +
> +	res = kstrtouint(val, 0, &sdebug_max_segment_size);
> +	if (res < 0)
> +		return res;
> +
> +	if (sdebug_max_segment_size < BLK_MIN_SEGMENT_SIZE)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static const struct kernel_param_ops max_segment_size_ops = {
> +	.set = sdebug_set_max_segment_size,
> +	.get = param_get_uint,
> +};
> +
>   static u32 sdebug_get_devsel(struct scsi_device *sdp)
>   {
>   	unsigned char devtype = sdp->type;
> @@ -7366,6 +7387,8 @@ 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_cb(max_segment_size, &max_segment_size_ops,
> +		&sdebug_max_segment_size, S_IRUGO);
>   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,
> @@ -7449,6 +7472,7 @@ 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_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(max_segment_size, "max bytes in a single DMA segment");
>   MODULE_PARM_DESC(medium_error_count, "count of sectors to return follow on MEDIUM error");
>   MODULE_PARM_DESC(medium_error_start, "starting sector number to return MEDIUM error");
>   MODULE_PARM_DESC(ndelay, "response delay in nanoseconds (def=0 -> ignore)");
> @@ -9539,7 +9563,6 @@ static const struct scsi_host_template sdebug_driver_template = {
>   	.sg_tablesize =		SG_MAX_SEGMENTS,
>   	.cmd_per_lun =		DEF_CMD_PER_LUN,
>   	.max_sectors =		-1U,
> -	.max_segment_size =	-1U,
>   	.module =		THIS_MODULE,
>   	.skip_settle_delay =	1,
>   	.track_queue_depth =	1,
> @@ -9566,6 +9589,7 @@ static int sdebug_driver_probe(struct device *dev)
>   	}
>   	hpnt->can_queue = sdebug_max_queue;
>   	hpnt->cmd_per_lun = sdebug_max_queue;
> +	hpnt->max_segment_size = sdebug_max_segment_size;
>   	if (!sdebug_clustering)
>   		hpnt->dma_boundary = PAGE_SIZE - 1;
>