On Wed, 2015-12-16 at 17:53 -0500, Martin K. Petersen wrote:
> 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.petersen@xxxxxxxxxx>
> ---
> 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.petersen@xxxxxxxxxx>
> +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;
Consider adding inline queue_max_dev_sectors() to blkdev.h and using it
in the line above?
> +
> + 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,
Reviewed-by: Ewan D. Milne <emilne@xxxxxxxxxx>
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