tomof at acm.org wrote on Sun, 19 Aug 2007 00:14 +0900:
> From: Pete Wyckoff <pw at osc.edu>
> Subject: Re: [Stgt-devel] [PATCH] iscsi fix xmit param
> Date: Sat, 18 Aug 2007 10:52:00 -0400
>
> > 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.
>
> session_keys[i].def doesn't change (it is always the iSCSI default
> value).
Understood, I wasn't assuming that. In fact, I toyed with adding
lots of "const" to enforce this, but it causes a big diff for not a
lot of benefit.
-- Pete
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