iSCSI: NOP-Out closing the command window

[Mark Bakke <mbakke@cisco.com>]

When sending a NOP-Out without the P bit set, there's
no response to update ExpCmdSN to keep the window open.

On an otherwise idle session, sending a long enough
sequence of these NOP-Outs can close the command window
permanently.

In case of a stuck command window, please break glass...

The easy solution is to turn on the P bit, and get the
responses to update the window, but that defaults the
purpose of allowing the P bit to not be set in the first
place.

Another easy solution (but I almost hate to mention it)
is not to have NOP-Out update the CmdSN.  This seems to
have the possibility of breaking other things.

I suppose we could come up with a more complicated rule,
like "if the NOP-Out's CmdSN would be the last (or perhaps
penultimate) CmdSN allowed by the current window, it MUST
set the P bit."  Or something like that.

Anyway, I see three possible solutions.  Any thoughts?

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054