[PATCH v12 2/3] blk-sysfs: add max_bio_bytes

[Changheun Lee]

Add max_bio_bytes block sysfs node to show current maximum bio size.

Signed-off-by: Changheun Lee <nanich.lee@xxxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-block | 10 ++++++++++
 Documentation/block/queue-sysfs.rst   |  7 +++++++
 block/blk-sysfs.c                     |  7 +++++++
 3 files changed, 24 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index e34cdeeeb9d4..8c8a793c04b4 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -316,3 +316,13 @@ Description:
 		does not complete in this time then the block driver timeout
 		handler is invoked. That timeout handler can decide to retry
 		the request, to fail it or to start a device recovery strategy.
+
+What:		/sys/block/<disk>/queue/max_bio_bytes
+Date:		June 2021
+Contact:	Changheun Lee <nanich.lee@xxxxxxxxxxx>
+Description:
+		max_bio_bytes is the maximum bio size to be submitted in bytes.
+		It shows current maximum bio size, and bio size to be submitted
+		will be limited with this. Default value is UINT_MAX, and
+		the minimum value is 1MB. 1MB(=BIO_MAX_VECS * PAGE_SIZE) is
+		legacy maximum bio size.
diff --git a/Documentation/block/queue-sysfs.rst b/Documentation/block/queue-sysfs.rst
index 4dc7f0d499a8..90af56899aa9 100644
--- a/Documentation/block/queue-sysfs.rst
+++ b/Documentation/block/queue-sysfs.rst
@@ -286,4 +286,11 @@ sequential zones of zoned block devices (devices with a zoned attributed
 that reports "host-managed" or "host-aware"). This value is always 0 for
 regular block devices.
 
+max_bio_bytes (RO)
+---------------------------
+This is the maximum number of bytes that bio size to be submitted will be
+limited. A value of 4,294,967,295(UINT_MAX) means no limit of bio size,
+and it's a default value. The minimum value is 1MB. It's legacy maximum
+bio size. (=BIO_MAX_VECS * PAGE_SIZE)
+
 Jens Axboe <jens.axboe@xxxxxxxxxx>, February 2009
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e03bedf180ab..c4cae6bbcb3b 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -108,6 +108,11 @@ queue_ra_store(struct request_queue *q, const char *page, size_t count)
 	return ret;
 }
 
+static ssize_t queue_max_bio_bytes_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(q->limits.max_bio_bytes, (page));
+}
+
 static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
 {
 	int max_sectors_kb = queue_max_sectors(q) >> 1;
@@ -577,6 +582,7 @@ static struct queue_sysfs_entry _prefix##_entry = {	\
 
 QUEUE_RW_ENTRY(queue_requests, "nr_requests");
 QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb");
+QUEUE_RO_ENTRY(queue_max_bio_bytes, "max_bio_bytes");
 QUEUE_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
 QUEUE_RO_ENTRY(queue_max_hw_sectors, "max_hw_sectors_kb");
 QUEUE_RO_ENTRY(queue_max_segments, "max_segments");
@@ -635,6 +641,7 @@ QUEUE_RW_ENTRY(queue_stable_writes, "stable_writes");
 static struct attribute *queue_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
+	&queue_max_bio_bytes_entry.attr,
 	&queue_max_hw_sectors_entry.attr,
 	&queue_max_sectors_entry.attr,
 	&queue_max_segments_entry.attr,
-- 
2.29.0