Re: how to do fc_remote_port_delete correctly

[Joe Eykholt <jeykholt-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

James Smart wrote:
> 
> James Smart wrote:
>> You never do set it to NULL. This is the role of the transport, and it 
>> will do so after calling the devloss_tmo_callbk(), which is the 
>> "end-of-life" indicator for the rport.
>>
>> If you are changing it - it can cause problems as the transport still 
>> has the rport active, may make other calls, etc until 
>> devloss_tmo_callbk() would occur.
>>
>>   
> Actually, it can cause other problems if you're changing dd_data.  The 
> transport will set it when it allocates the rport. As the rport can also 
> be used as a container for the scsi tgt id bindings, and later reused if 
> the same device comes back post devloss_tmo (in which case, it "appears" 
> as a new rport to the LLDD). In this case, if you are NULL-ing the 
> dd_data value, you've hosed the structure for the later use.  Let the 
> tansport manage the dd_data value, you can manage the contents pointed 
> to by dd_data.

I see what you mean and agree.

It seems like there are two slightly different sets of rules depending
on whether dd_fcrport_size is zero or not, as specified by the LLDD.

In the first model, where dd_fcrport_size is zero, the transport
never sets dd_data at all.  My understanding now is that its OK
for the LLDD to set it non-NULL, but not OK to change it after that.
I guess it would be OK but unnecessary to NULL it at dev_loss timeout
just before freeing the attached context.  These are the usage rules
I didn't fully understand. These rules are really established by
how the LLDDs I/O routines use dd_data.

In the second model, it doesn't seem like the LLDD has full control over
the contents pointed to by dd_data either, since when the remote
port is re-added the area pointed to by dd_data is cleared by the
transport, so we always start fresh.  This is fine, but has
implications on how the context is used during devloss.  For example,
it shouldn't be used for list linkage unless it's unlinked
before fc_remote_port_add.  All that's in the LLDDs control, so it's OK.

For libfc, I'm leaning towards continuing to use a non-zero dd_fcrport_size
and the fc_rport_libfc_priv struct.   libfc could use a separately
allocated struct like fc_disc_rport for the discovery and
rport (PLOGI, PRLI, etc.) state machines.

This is all an effort to clean up some issues caused by creating "rogue"
fc_rports in libfc so that we would always have both an fc_rport_libfc_priv
and an fc_rport allocated together, even before fc_remote_port_add().
It causes issues when we do remote_port_add and have to transition
the state from the rogue to the "real" rport.
In the meantime, the rogue could still be accessed by incoming requests,
or new RSCNs, and those changes wouldn't get reflected to the real rport.
It's messy, and hard to analyze all the potential problems, so I'm
trying to fix that.

I really appreciate your help!  Thanks a bunch!

	Joe