MFC r313854, r313963: Change the way MaxCmdSN is used.

Before this change MaxCmdSN was reported as CmdSN + delta, that made it
limit number of requests in transmission from the initiator to target,
that was pretty useless.  After this change MaxCmdSN limits number of
requests queued to CTL, i.e. maximal queue depth for the initiator.
The default limit is 256 outstanding requests per initiator at a time.

This code uses existing cs_outstanding_ctl_pdus counter to track queue
depth.  It's semantics doen't perfectly match, but close enough to not
add another counter.  Just don't set the maxtags below 2.

1 files changed, 6 insertions, 6 deletions

diff --git a/sys/cam/ctl/ctl_frontend_iscsi.c b/sys/cam/ctl/ctl_frontend_iscsi.c
index 72580e9..bd85576 100644
--- a/sys/cam/ctl/ctl_frontend_iscsi.c
+++ b/sys/cam/ctl/ctl_frontend_iscsi.c
@@ -95,10 +95,9 @@ SYSCTL_INT(_kern_cam_ctl_iscsi, OID_AUTO, ping_timeout, CTLFLAG_RWTUN,
 static int login_timeout = 60;
 SYSCTL_INT(_kern_cam_ctl_iscsi, OID_AUTO, login_timeout, CTLFLAG_RWTUN,
     &login_timeout, 60, "Time to wait for ctld(8) to finish Login Phase, in seconds");
-static int maxcmdsn_delta = 256;
-SYSCTL_INT(_kern_cam_ctl_iscsi, OID_AUTO, maxcmdsn_delta, CTLFLAG_RWTUN,
-    &maxcmdsn_delta, 256, "Number of commands the initiator can send "
-    "without confirmation");
+static int maxtags = 256;
+SYSCTL_INT(_kern_cam_ctl_iscsi, OID_AUTO, maxtags, CTLFLAG_RWTUN,
+    &maxtags, 0, "Max number of requests queued by initiator");
 
 #define	CFISCSI_DEBUG(X, ...)						\
 	do {								\
@@ -244,7 +243,7 @@ cfiscsi_pdu_update_cmdsn(const struct icl_pdu *request)
 		 * outside of this range.
 		 */
 		if (ISCSI_SNLT(cmdsn, cs->cs_cmdsn) ||
-		    ISCSI_SNGT(cmdsn, cs->cs_cmdsn + maxcmdsn_delta)) {
+		    ISCSI_SNGT(cmdsn, cs->cs_cmdsn - 1 + maxtags)) {
 			CFISCSI_SESSION_UNLOCK(cs);
 			CFISCSI_SESSION_WARN(cs, "received PDU with CmdSN %u, "
 			    "while expected %u", cmdsn, cs->cs_cmdsn);
@@ -399,7 +398,8 @@ cfiscsi_pdu_prepare(struct icl_pdu *response)
 	    (bhssr->bhssr_flags & BHSDI_FLAGS_S))
 		bhssr->bhssr_statsn = htonl(cs->cs_statsn);
 	bhssr->bhssr_expcmdsn = htonl(cs->cs_cmdsn);
-	bhssr->bhssr_maxcmdsn = htonl(cs->cs_cmdsn + maxcmdsn_delta);
+	bhssr->bhssr_maxcmdsn = htonl(cs->cs_cmdsn - 1 +
+	    imax(0, maxtags - cs->cs_outstanding_ctl_pdus));
 
 	if (advance_statsn)
 		cs->cs_statsn++;