block/loop: add documentation for sysfs interface

Documentation has been compiled from git logs and by reading through
code.

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

diff --git a/Documentation/ABI/testing/sysfs-block-loop b/Documentation/ABI/testing/sysfs-block-loop
new file mode 100644 (file)
index 0000000..627f4eb
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+++ b/Documentation/ABI/testing/sysfs-block-loop
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+What:          /sys/block/loopX/loop/autoclear
+Date:          Aug, 2010
+KernelVersion: v2.6.37
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) Shows if the device is in autoclear mode or not ( "1" or
+               "0"). Autoclear (if set) indicates that the loopback device will
+               self-distruct after last close.
+
+What:          /sys/block/loopX/loop/backing_file
+Date:          Aug, 2010
+KernelVersion: v2.6.37
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) The path of the backing file that the loop device maps its
+               data blocks to.
+
+What:          /sys/block/loopX/loop/offset
+Date:          Aug, 2010
+KernelVersion: v2.6.37
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) Start offset (in bytes).
+
+What:          /sys/block/loopX/loop/sizelimit
+Date:          Aug, 2010
+KernelVersion: v2.6.37
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) The size (in bytes) that the block device maps, starting
+               from the offset.
+
+What:          /sys/block/loopX/loop/partscan
+Date:          Aug, 2011
+KernelVersion: v3.10
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) Shows if automatic partition scanning is enabled for the
+               device or not ("1" or "0"). This can be requested individually
+               per loop device during its setup by setting LO_FLAGS_PARTSCAN in
+               in the ioctl request. By default, no partition tables are
+               scanned.
+
+What:          /sys/block/loopX/loop/dio
+Date:          Aug, 2015
+KernelVersion: v4.10
+Contact:       linux-block@vger.kernel.org
+Description:
+               (RO) Shows if direct IO is being used to access backing file or
+               not ("1 or "0").