[PATCH V4 6/8] null_blk: add param to set max disacrd sectors

[Chaitanya Kulkarni]

Instead of hardcoding value for the maximum discard sector to
UINT_MAX >> 9, allow user to set the value with newly added module
parameter max_discard_sectors.

To retain the backward compatibility make set default value to
UINT_MAX >> 9.

Signed-off-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>
---
 drivers/block/null_blk/main.c     | 10 +++++++++-
 drivers/block/null_blk/null_blk.h |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 96b8aca5abda..2f787807cf63 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -216,6 +216,10 @@ static bool g_discard;
 module_param_named(discard, g_discard, bool, 0444);
 MODULE_PARM_DESC(discard, "Support discard operations (requires memory-backed null_blk device). Default: false");
 
+static unsigned int g_max_discard_sectors = UINT_MAX >> 9;
+module_param_named(max_discard_sectors, g_max_discard_sectors, uint, 0444);
+MODULE_PARM_DESC(max_discard_sectors, "Maximum size of a REQ_OP_DISCARD command (in 512B sectors).");
+
 static bool g_write_zeroes;
 module_param_named(write_zeroes, g_write_zeroes, bool, 0444);
 MODULE_PARM_DESC(write_zeroes, "Support write-zeores operations. Default: false");
@@ -420,6 +424,7 @@ NULLB_DEVICE_ATTR(home_node, uint, NULL);
 NULLB_DEVICE_ATTR(queue_mode, uint, NULL);
 NULLB_DEVICE_ATTR(blocksize, uint, NULL);
 NULLB_DEVICE_ATTR(max_sectors, uint, NULL);
+NULLB_DEVICE_ATTR(max_discard_sectors, uint, NULL);
 NULLB_DEVICE_ATTR(irqmode, uint, NULL);
 NULLB_DEVICE_ATTR(hw_queue_depth, uint, NULL);
 NULLB_DEVICE_ATTR(index, uint, NULL);
@@ -544,6 +549,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
 	&nullb_device_attr_queue_mode,
 	&nullb_device_attr_blocksize,
 	&nullb_device_attr_max_sectors,
+	&nullb_device_attr_max_discard_sectors,
 	&nullb_device_attr_irqmode,
 	&nullb_device_attr_hw_queue_depth,
 	&nullb_device_attr_index,
@@ -686,6 +692,7 @@ static struct nullb_device *null_alloc_dev(void)
 	dev->queue_mode = g_queue_mode;
 	dev->blocksize = g_bs;
 	dev->max_sectors = g_max_sectors;
+	dev->max_discard_sectors = g_max_discard_sectors;
 	dev->irqmode = g_irqmode;
 	dev->hw_queue_depth = g_hw_queue_depth;
 	dev->blocking = g_blocking;
@@ -1850,7 +1857,8 @@ static void null_config_discard(struct nullb *nullb)
 	}
 
 	nullb->q->limits.discard_granularity = nullb->dev->blocksize;
-	blk_queue_max_discard_sectors(nullb->q, UINT_MAX >> 9);
+	blk_queue_max_discard_sectors(nullb->q,
+				      nullb->dev->max_discard_sectors);
 }
 
 static void null_config_write_zeroes(struct nullb *nullb)
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 2c0c9c29158f..09940211326d 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -102,6 +102,7 @@ struct nullb_device {
 	unsigned int queue_mode; /* block interface */
 	unsigned int blocksize; /* block size */
 	unsigned int max_sectors; /* Max sectors per command */
+	unsigned int max_discard_sectors; /* Max discard sectors per command */
 	unsigned int irqmode; /* IRQ completion handler */
 	unsigned int hw_queue_depth; /* queue depth */
 	unsigned int index; /* index of the disk, only valid with a disk */
-- 
2.29.0