On an RSCN event, the nodes specified in RSCN payload and in MAPPED state
are moved to NPR state in order to revalidate the login. This triggers an
immediate unregister from SCSI/NVMe backend. The assumption is that the
node may be missing. The re-registration with the backend happens after
either relogin (PLOGI/PRLI; if ADISC is disabled or login truly lost) or
when ADISC completes successfully (rediscover with ADISC enabled).

However, the NVMe-FC standard provides for an RSCN to be triggered when
the remote port supports a discovery controller and there was a change
of discovery log content. As the remote port typically also supports
storage subsystems, this unregister causes all storage controller
connections to fail and require reconnect.

Correct by reworking the code to ensure that the unregistration only occurs
when a login state is truly terminated, thereby leaving the NVMe storage
controllers in place.

The changes made are:

 - Retain node state in ADISC_ISSUE when scheduling ADISC ELS retry.

 - Do not clear wwpn/wwnn values upon ADISC failure.

 - Move MAPPED nodes to NPR during RSCN processing, but do not unregister
   with transport.  On GIDFT completion, identify missing nodes (not marked
   NLP_NPR_2B_DISC) and unregister them.

 - Perform unregistration for nodes that will go through ADISC processing
   if ADISC completion fails.

 - Successful ADISC completion will move node back to MAPPED state.

Link: https://lore.kernel.org/r/20210707184351.67872-16-jsmart2021@gmail.comCo-developed-by: NJustin Tee <justin.tee@broadcom.com>
Signed-off-by: NJustin Tee <justin.tee@broadcom.com>
Signed-off-by: NJames Smart <jsmart2021@gmail.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>