Some storage devices report a maximum transfer length which indicates
the maximum size of an I/O request that the device can process. This
limit is enforced in combination with the controller's max_hw_sectors
and DMA constraints to ensure that we do not issue a command too big for
the device.
Export the max_dev_sectors_kb queue limit in sysfs and update the
documentation accordingly.
Signed-off-by: Martin K. Petersen <martin.peter...@oracle.com>
---
Documentation/ABI/testing/sysfs-block | 9 +++++++++
Documentation/block/queue-sysfs.txt | 11 +++++++++--
block/blk-settings.c | 4 +++-
block/blk-sysfs.c | 13 +++++++++++++
4 files changed, 34 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-block
b/Documentation/ABI/testing/sysfs-block
index 71d184dbb70d..4f284d38c085 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -235,3 +235,12 @@ Description:
write_same_max_bytes is 0, write same is not supported
by the device.
+What: /sys/block/<disk>/queue/max_dev_sectors_kb
+Date: December 2015
+Contact: Martin K. Petersen <martin.peter...@oracle.com>
+Description:
+ Some storage devices report the maximum size that the
+ device can process in a single READ or WRITE
+ request. This limit is used in combination with
+ constraints set by the controller driver to limit the
+ size of filesystem requests.
diff --git a/Documentation/block/queue-sysfs.txt
b/Documentation/block/queue-sysfs.txt
index e5d914845be6..a078995f3eae 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -55,9 +55,15 @@ logical_block_size (RO)
-----------------------
This is the logcal block size of the device, in bytes.
+max_dev_sectors_kb (R)
+----------------------
+This is the maximum number of kilobytes supported by the storage device
+for a READ or WRITE request.
+
max_hw_sectors_kb (RO)
----------------------
-This is the maximum number of kilobytes supported in a single data transfer.
+This is the maximum number of kilobytes supported by the storage
+controller in a single data transfer.
max_integrity_segments (RO)
---------------------------
@@ -68,7 +74,8 @@ max_sectors_kb (RW)
-------------------
This is the maximum number of kilobytes that the block layer will allow
for a filesystem request. Must be smaller than or equal to the maximum
-size allowed by the hardware.
+size allowed by the storage controller (max_hw_sectors_kb) and the
+maximum size allowed by the storage device (max_dev_sectors_kb).
max_segments (RO)
-----------------
diff --git a/block/blk-settings.c b/block/blk-settings.c
index dd4973583978..362b0179c86a 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -232,7 +232,9 @@ EXPORT_SYMBOL(blk_queue_bounce_limit);
* max_sectors is a soft limit imposed by the block layer for
* filesystem type requests. This value can be overridden on a
* per-device basis in /sys/block/<device>/queue/max_sectors_kb.
- * The soft limit can not exceed max_hw_sectors.
+ *
+ * The soft limit's lower bound is the page cache size and it can not
+ * exceed neither max_hw_sectors, nor max_dev_sectors.
**/
void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int
max_hw_sectors)
{
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e140cc487ce1..c289f9f6dcd9 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -225,6 +225,13 @@ static ssize_t queue_max_hw_sectors_show(struct
request_queue *q, char *page)
return queue_var_show(max_hw_sectors_kb, (page));
}
+static ssize_t queue_max_dev_sectors_show(struct request_queue *q, char *page)
+{
+ int max_dev_sectors_kb = q->limits.max_dev_sectors >> 1;
+
+ return queue_var_show(max_dev_sectors_kb, (page));
+}
+
#define QUEUE_SYSFS_BIT_FNS(name, flag, neg) \
static ssize_t \
queue_show_##name(struct request_queue *q, char *page) \
@@ -371,6 +378,11 @@ static struct queue_sysfs_entry queue_max_hw_sectors_entry
= {
.show = queue_max_hw_sectors_show,
};
+static struct queue_sysfs_entry queue_max_dev_sectors_entry = {
+ .attr = {.name = "max_dev_sectors_kb", .mode = S_IRUGO },
+ .show = queue_max_dev_sectors_show,
+};
+
static struct queue_sysfs_entry queue_max_segments_entry = {
.attr = {.name = "max_segments", .mode = S_IRUGO },
.show = queue_max_segments_show,
@@ -483,6 +495,7 @@ static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
&queue_max_hw_sectors_entry.attr,
+ &queue_max_dev_sectors_entry.attr,
&queue_max_sectors_entry.attr,
&queue_max_segments_entry.attr,
&queue_max_integrity_segments_entry.attr,
--
2.5.0
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