[Stgt-devel] [PATCH] iscsi fix xmit param

[Pete Wyckoff]

tomof at acm.org wrote on Sat, 18 Aug 2007 14:10 +0900:
> From: Pete Wyckoff <pw at osc.edu>
> Subject: Re: [Stgt-devel] [PATCH] iscsi fix xmit param
> Date: Wed, 15 Aug 2007 11:15:59 -0500
>
> > True.  There are a few cases.
> > 
> > 1.  ini sends mrdsl > target mxdsl.  Apply minimum, use target max.
> > 2.  ini sends mrdsl < target mxdsl.  Apply minimum, use ini max.
> > 3.  ini does not mention mrdsl.  Target should set its mxdsl to the
> >     standard default (8192), not use its default max.
> > 
> > This last case was broken before my earlier patch "iscsi param
> > cleanup".  Now it is fixed but I changed the target default to 8k.
> > I want the target to agree to use a larger value if the initiator is
> > willing, but still get case #3 correct if the initiator does not
> > specify.
> 
> Really?
> 
> I think that if ini does not mention mrdsl and target doesn't use the
> standard default mxdsl value (a target admin sets non default value),
> text_check_param() sets xmdsl to the default value.

It really was broken.  But this is an odd case as open-iscsi at
least always sends mrdsl, even if it is set to use the default.

If you roll back to 92d767a711ed82791b171ce7c9b722263076c519 or so,
just before "iscsi param cleanup" you'll see:

iscsi/param.c:   mxdsl = 262144
iscsi/target.c:  mxdsl = 8192

and this code in iscsi/iscsid.c:

	if (p[i].state == KEY_STATE_START && p[i].val != session_keys[i].def) {
		if (conn->state == STATE_LOGIN) {
			if (i == ISCSI_PARAM_MAX_XMIT_DLENGTH) {
				if (p[i].val > session_keys[i].def)
					p[i].val = session_keys[i].def;
				p[i].state = KEY_STATE_DONE;
				continue;
			}
			memset(buf, 0, sizeof(buf));
			param_val_to_str(session_keys, i, p[i].val,
					 buf);
			text_key_add(conn, session_keys[i].name, buf);
			p[i].state = KEY_STATE_REQUEST;
		}
		cnt++;
	}

(p[] is conn->session_param, which is initialized from target params
then modified by negotiation.)

If target admin does not change target mxdsl, and initiator does not
send mrdsl, this code will see 8192 != 262144 and use 8192.  Fine,
that's the default.

If target admin changes target mxdsl to 16384 using tgtadm, and
initiator does not send mrdsl, this code will see 16384 != 262144
and use 16384 without negotiation.  Bad, should use the default.

With the "iscsi param cleanup" patch and this new "iscsi fix xmit
param", I think everything works as it should.

		-- Pete