The SAS transport class ABI is currently undocumented.

Some systemd issues have been raised for SAS device support [1], [2].

Because of this, distros using systemd may have broken symlinks, like
/dev/disk/by-path

Unfortunately it is challenging to support SAS devices as the ABI is not well
documented and is not always intuitive, so add a stable ABI definition.

[1] https://github.com/systemd/systemd/issues/3943#issuecomment-240982482
[2] https://github.com/systemd/systemd/issues/7157

Signed-off-by: John Garry <[email protected]>
--

I am sending this as an incomplete RFC to ensure it's the right thing to do, so
I don't bother writing the document to find it later rejected.

For now, this is just a minimal effort.

diff --git a/Documentation/ABI/stable/sysfs-transport-sas 
b/Documentation/ABI/stable/sysfs-transport-sas
new file mode 100644
index 0000000..6df6ffe
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-transport-sas
@@ -0,0 +1,21 @@
+What:          /sys/class/sas_phy/phy-<host>:<phy identifier>,
+                                  phy-<host>:<scsi target id>:<phy identifier>
+Date:          Nov, 2018
+KernelVersion: 2.6.13
+Contact:       [email protected]
+Description:   SAS PHY entry directory, which includes interfaces to control
+               the PHY, physical layer information on the PHY, and other SAS
+               fabric management information asscoiated with the PHY.
+
+What:          /sys/class/sas_port/port-<host>:<port identifier>,
+                                   port-<host>:<scsi target id>:<port 
identifier>
+Date:          Nov, 2018
+KernelVersion: 2.6.13
+Contact:       [email protected]
+Description:   SAS Port entry directory, with constituient PHY count and
+               other SAS fabric management information asscoiated with the
+               Port.
+
+
+
+
-- 
1.9.1

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