docs: sysfs-block: document virt_boundary_mask

/sys/block/<disk>/queue/virt_boundary_mask is completely undocumented.
Document it.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20211209003833.6396-7-ebiggers@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 288626e8cb5323ffc7049e1b0fe3e24ac21bd2eb..8dd3e84a8aade7f47140c2b0fdb39e986caa0913 100644 (file)
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -544,6 +544,18 @@ Description:
                CONFIG_BLK_DEV_THROTTLING_LOW is enabled.
 
 
+What:          /sys/block/<disk>/queue/virt_boundary_mask
+Date:          April 2021
+Contact:       linux-block@vger.kernel.org
+Description:
+               [RO] This file shows the I/O segment memory alignment mask for
+               the block device.  I/O requests to this device will be split
+               between segments wherever either the memory address of the end
+               of the previous segment or the memory address of the beginning
+               of the current segment is not aligned to virt_boundary_mask + 1
+               bytes.
+
+
 What:          /sys/block/<disk>/queue/wbt_lat_usec
 Date:          November 2016
 Contact:       linux-block@vger.kernel.org