[PATCH v2] scsi_debug: Support configuring the maximum segment size

[Bart Van Assche <bvanassche@acm.org>]

Add a kernel module parameter for configuring the maximum segment size.
Note: blk_validate_limits() considers zero as the default and changes it
into a valid value. Values between 1 and BLK_MIN_SEGMENT_SIZE are rejected
by blk_validate_limits().

This patch enables testing SCSI support for segments smaller than the
page size.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
Cc: John Garry <john.g.garry@oracle.com>
Cc: Doug Gilbert <dgilbert@interlog.com>

Changes compared to v1:
 - Removed sdebug_driver_template.max_segment_size.
 - Changed the default max_segment_size value from BLK_MAX_SEGMENT_SIZE into
   UINT_MAX (this is the same as the current limit, -1U).
 - Explained in the patch description that blk_validate_limits() rejects
   values between 1 and BLK_MIN_SEGMENT_SIZE.

 drivers/scsi/scsi_debug.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 1515495fd9ea..44309a16eb68 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 */
@@ -7366,6 +7367,7 @@ 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_segment_size, sdebug_max_segment_size, uint, 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 +7451,7 @@ 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 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 +9542,6 @@ 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 +9568,7 @@ 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;