PDU use serial32 arithmetic for cmdsn, maxcmdsn and expcmdsn.

RFC3720 says that cmdsn comparison must be done using
serial32 arithmetic. This will definetly avoid a deadlock
if cmdsn wraps from 2^32-1 to 0.

Signed-off-by: Peter Lieven <pl@kamp.de>

include/iscsi-private.h

@@ -325,6 +325,9 @@ iscsi_log_message(struct iscsi_context *iscsi, int level, const char *format, ..
 void
 iscsi_add_to_outqueue(struct iscsi_context *iscsi, struct iscsi_pdu *pdu);
 
+int
+iscsi_serial32_compare(u_int32_t s1, u_int32_t s2);
+
 #ifdef __cplusplus
 }
 #endif

lib/iscsi-command.c

@@ -335,7 +335,7 @@ iscsi_process_scsi_reply(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
 	}
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}
 
@@ -452,7 +452,7 @@ iscsi_process_scsi_data_in(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
 	}
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}
 
@@ -542,7 +542,7 @@ iscsi_process_r2t(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
 	len    = scsi_get_uint32(&in->hdr[44]);
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}
 

lib/login.c

@@ -950,10 +950,10 @@ iscsi_process_login_reply(struct iscsi_context *iscsi, struct iscsi_pdu *pdu,
 	iscsi->statsn = scsi_get_uint16(&in->hdr[24]);
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}
-
+	
 	/* XXX here we should parse the data returned in case the target
 	 * renegotiated some some parameters.
 	 *  we should also do proper handshaking if the target is not yet
@@ -1136,7 +1136,7 @@ struct iscsi_in_pdu *in)
 	uint32_t maxcmdsn;
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}
 

lib/pdu.c

@@ -30,6 +30,24 @@
 #include "scsi-lowlevel.h"
 #include "slist.h"
 
+/* This adds 32-bit serial comparision as defined in RFC1982.
+ * It returns 0 for equality, 1 if s1 is greater than s2 and
+ * -1 if s1 is less than s2. According to RFC1982 section 3.2
+ * there are rare cases where the result of the comparision is
+ * undefined e.g. when s1 = 0 and s2=2^31. This cases should
+ * not happen in iSCSI protocol.
+ */
+int
+iscsi_serial32_compare(u_int32_t s1, u_int32_t s2) {
+	if (s1 == s2) return 0;
+	if (s1 < s2 && s2-s1 < (u_int32_t)1<<31) return -1;
+	if (s1 > s2 && s1-s2 < (u_int32_t)1<<31) return 1;
+	if (s1 > s2 && s1-s2 > (u_int32_t)1<<31) return -1;
+	if (s1 < s2 && s2-s1 > (u_int32_t)1<<31) return 1;
+	/* undefined result */
+	return -1;
+}
+
 struct iscsi_pdu *
 iscsi_allocate_pdu_with_itt_flags_size(struct iscsi_context *iscsi, enum iscsi_opcode opcode,
 				  enum iscsi_opcode response_opcode, uint32_t itt, uint32_t flags, size_t payload_size)

lib/socket.c

@@ -302,7 +302,7 @@ iscsi_which_events(struct iscsi_context *iscsi)
 {
 	int events = iscsi->is_connected ? POLLIN : POLLOUT;
 
-	if (iscsi->outqueue && iscsi->outqueue->cmdsn <= iscsi->maxcmdsn) {
+	if (iscsi->outqueue && iscsi_serial32_compare(iscsi->outqueue->cmdsn,iscsi->maxcmdsn) <= 0) {
 	 	events |= POLLOUT;
 	}
 	return events;
@@ -442,7 +442,7 @@ iscsi_write_to_socket(struct iscsi_context *iscsi)
 	while (iscsi->outqueue) {
 		ssize_t total;
 
-		if (iscsi->outqueue->cmdsn > iscsi->maxcmdsn) {
+		if (iscsi_serial32_compare(iscsi->outqueue->cmdsn,iscsi->maxcmdsn) > 0) {
 			/* stop sending. maxcmdsn is reached */
 			return 0;
 		}

lib/task_mgmt.c

@@ -88,7 +88,7 @@ iscsi_process_task_mgmt_reply(struct iscsi_context *iscsi, struct iscsi_pdu *pdu
 	response = in->hdr[2];
 
 	maxcmdsn = scsi_get_uint32(&in->hdr[32]);
-	if (maxcmdsn > iscsi->maxcmdsn) {
+	if (iscsi_serial32_compare(maxcmdsn,iscsi->maxcmdsn) > 0) {
 		iscsi->maxcmdsn = maxcmdsn;
 	}