Application A has registered a diag buffer and looking for particular event
to happen to release & read the trace buffer. Meanwhile application B has
unregistered the diag buffer and now Application A can't get the required
diag buffer. So proper diag buffer ownership is missing.

Each application has to maintain its own Unique ID. Now driver has to save
the Application's UniqueID for each diag buffer type when diag buffer is
registered. And driver has to allow 'release', 'read' & 'unregister' diag
commands only if application's UniqueID matches with saved UniqueID for the
corresponding diag buffer type.

When diag buffer is registered by the driver, then the UniqueID saved by
the driver is "BRCM" (i.e. 0x4252434D) for SAS3 and above generations HBA
devices. For SAS2 HBAs, driver keeps the legacy UniqueID 0x07075900 for
maintaining compatibility with the legacy SAS2 application and this
improvement won't be applicable for SAS2 HBA devices.

Any application can own the buffer registered by the driver by sending
diag register request to driver with same buffer type and size
(Application can get the buffer size by sending 'query' command). Then
driver changes the ownership of the buffer by saving application's
UniqueID for that corresponding buffer type.

Also, application can re-register the diag buffer with same size without
un-registering it, but diag buffer should be released before re-registering
it. By allowing this, driver no need to deallocate and allocate a new
buffer for re-register command, same buffer can be re-used.

Link: https://lore.kernel.org/r/1568379890-18347-6-git-send-email-sreekanth.reddy@broadcom.comSigned-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>