Re: ISCSI: CmdSN in non-leading login

["Mark S. Edwards" <marke@muttsnuts.com>]

At 09:13 AM 5/10/2002 -0700, Bill Studenmund wrote:
>On Fri, 10 May 2002, Mark S. Edwards wrote:
>
> > There are a couple of problems here for the target.  At what point is a
> > non-leading connection considered to be part of the session ?  Is it the
> > moment that the login request is received with a non-zero TSIH ?  Or is it
> > only when the non-leading login succeeds and it enters full feature phase ?
>
>I think the target shouldn't let anything from a new connection influence
>things until after at least the security phase has been passed. Otherwise
>we have a security hole. After operational negotiation would probably be
>best.

Good, as far as I can see, a new connection should not be allowed to 
influence any session context until the connection reached full-feature 
phase.  But this is a problem if we have to follow the CmdSN rules of 
9.12.8.   See next comment.


> > So, should an initiator set the CmdSN in the first login request to zero
> > and only synchronise with the session command stream after full feature
> > phase is established ?  This is my preferred option.
> >
> > What happens if the initiator tries using the current session command
> > sequence number is that whilst the login negotiation occurs, other
> > connections within the session can be issuing new commands, so by the time
> > that the login is finished the CmdSN exchanged in the initial request is
> > invalid anyway.
> >
> > I would like to see something along the lines that for a non-leading
> > connection, the CmdSN field MUST be zero and that the connection can not be
> > considered part of the session until full feature phase is entered, at
> > which point any commands issued on the connection are now synchronised with
> > the session command sequence number as observed by all other existing
> > connections on the session.
>
>I thought login counted as a command, so it got its own command number, in
>the stream of all other commands. ??


For a leading connection the CmdSN, whether zero or non-zero, is regarded 
as a primer with which to set the initial session command sequence number, 
all the login requests exchanged in the negotiation, no matter how many 
carry the same CmdSN as does the first non-immediate command.  In other 
words, the first pdu in a leading connection does influence session state.

So if we agree that a non-leading connection can not influence session 
state until full-feature phase, then we have to also state that the rule in 
9.12.8 about the first non-immediate command carrying the same CmdSN as the 
initial login request can not work for a non-leading connection.  In this 
case, the first non-immediate command must be set from the next logical 
value in the session context.  I would like the spec to have this added and 
to explicitly say that the CmdSN in a login request for a non-leading 
connection is ignored by the target.  I'd really prefer that the actual 
value be zero, but that's not necessary from a protocol perspective if the 
target ignores the field.

Mark.