[PATCH v2 8/8] null_blk: Support configuring the maximum segment size

Bart Van Assche
2022-11-23T20:58:31Z

Add support for configuring the maximum segment size.

Add support for segments smaller than the page size.

This patch enables testing segments smaller than the page size with a
driver that does not call blk_rq_map_sg().

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
drivers/block/null_blk/main.c | 20 +++++++++++++++++---
drivers/block/null_blk/null_blk.h | 1 +
2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 1f154f92f4c2..bc811ab52c4a 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -157,6 +157,10 @@ static int g_max_sectors;
module_param_named(max_sectors, g_max_sectors, int, 0444);
MODULE_PARM_DESC(max_sectors, "Maximum size of a command (in 512B sectors)");

+static unsigned int g_max_segment_size = 1UL << 31;
+module_param_named(max_segment_size, g_max_segment_size, int, 0444);
+MODULE_PARM_DESC(max_segment_size, "Maximum size of a segment in bytes");
+
static unsigned int nr_devices = 1;
module_param(nr_devices, uint, 0444);
MODULE_PARM_DESC(nr_devices, "Number of devices to register");
@@ -409,6 +413,7 @@ 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_segment_size, uint, NULL);
NULLB_DEVICE_ATTR(irqmode, uint, NULL);
NULLB_DEVICE_ATTR(hw_queue_depth, uint, NULL);
NULLB_DEVICE_ATTR(index, uint, NULL);
@@ -532,6 +537,7 @@ 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_segment_size,
&nullb_device_attr_irqmode,
&nullb_device_attr_hw_queue_depth,
&nullb_device_attr_index,
@@ -610,7 +616,8 @@ static ssize_t memb_group_features_show(struct config_item *item, char *page)
return snprintf(page, PAGE_SIZE,
"badblocks,blocking,blocksize,cache_size,"
"completion_nsec,discard,home_node,hw_queue_depth,"
- "irqmode,max_sectors,mbps,memory_backed,no_sched,"
+ "irqmode,max_sectors,max_segment_size,mbps,"
+ "memory_backed,no_sched,"
"poll_queues,power,queue_mode,shared_tag_bitmap,size,"
"submit_queues,use_per_node_hctx,virt_boundary,zoned,"
"zone_capacity,zone_max_active,zone_max_open,"
@@ -673,6 +680,7 @@ 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_segment_size = g_max_segment_size;
dev->irqmode = g_irqmode;
dev->hw_queue_depth = g_hw_queue_depth;
dev->blocking = g_blocking;
@@ -1214,6 +1222,8 @@ static int null_transfer(struct nullb *nullb, struct page *page,
unsigned int valid_len = len;
int err = 0;

+ WARN_ONCE(len > dev->max_segment_size, "%u > %u\n", len,
+ dev->max_segment_size);
if (!is_write) {
if (dev->zoned)
valid_len = null_zone_valid_read_len(nullb,
@@ -1249,7 +1259,8 @@ static int null_handle_rq(struct nullb_cmd *cmd)

spin_lock_irq(&nullb->lock);
rq_for_each_segment(bvec, rq, iter) {
- len = bvec.bv_len;
+ len = min(bvec.bv_len, nullb->dev->max_segment_size);
+ bvec.bv_len = len;
err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset,
op_is_write(req_op(rq)), sector,
rq->cmd_flags & REQ_FUA);
@@ -1276,7 +1287,8 @@ static int null_handle_bio(struct nullb_cmd *cmd)

spin_lock_irq(&nullb->lock);
bio_for_each_segment(bvec, bio, iter) {
- len = bvec.bv_len;
+ len = min(bvec.bv_len, nullb->dev->max_segment_size);
+ bvec.bv_len = len;
err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset,
op_is_write(bio_op(bio)), sector,
bio->bi_opf & REQ_FUA);
@@ -2088,6 +2100,7 @@ static int null_add_dev(struct nullb_device *dev)
nullb->q->queuedata = nullb;
blk_queue_flag_set(QUEUE_FLAG_NONROT, nullb->q);
blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, nullb->q);
+ blk_queue_flag_set(QUEUE_FLAG_SUB_PAGE_SEGMENTS, nullb->q);

mutex_lock(&lock);
rv = ida_simple_get(&nullb_indexes, 0, 0, GFP_KERNEL);
@@ -2106,6 +2119,7 @@ static int null_add_dev(struct nullb_device *dev)
dev->max_sectors = min_t(unsigned int, dev->max_sectors,
BLK_DEF_MAX_SECTORS);
blk_queue_max_hw_sectors(nullb->q, dev->max_sectors);
+ blk_queue_max_segment_size(nullb->q, dev->max_segment_size);

if (dev->virt_boundary)
blk_queue_virt_boundary(nullb->q, PAGE_SIZE - 1);
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 94ff68052b1e..6784ee9f5fda 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_segment_size; /* Max size of a single DMA segment. */
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 */