scsi: zfcp: fix capping of unsuccessful GPN_FT SAN response trace records

v4.9 commit aceeffbb59bb ("zfcp: trace full payload of all SAN records
(req,resp,iels)") fixed trace data loss of 2.6.38 commit 2c55b750a884
("[SCSI] zfcp: Redesign of the debug tracing for SAN records.")
necessary for problem determination, e.g. to see the
currently active zone set during automatic port scan.

While it already saves space by not dumping any empty residual entries
of the large successful GPN_FT response (4 pages), there are seldom cases
where the GPN_FT response is unsuccessful and likely does not have
FC_NS_FID_LAST set in fp_flags so we did not cap the trace record.
We typically see such case for an initiator WWPN, which is not in any zone.

Cap unsuccessful responses to at least the actual basic CT_IU response
plus whatever fits the SAN trace record built-in "payload" buffer
just in case there's trailing information
of which we would at least see the existence and its beginning.

In order not to erroneously cap successful responses, we need to swap
calling the trace function and setting the CT / ELS status to success (0).

Example trace record pair formatted with zfcpdbf:

Timestamp      : ...
Area           : SAN
Subarea        : 00
Level          : 1
Exception      : -
CPU ID         : ..
Caller         : 0x...
Record ID      : 1
Tag            : fssct_1
Request ID     : 0x<request_id>
Destination ID : 0x00fffffc
SAN req short  : 01000000 fc020000 01720ffc 00000000
                 00000008
SAN req length : 20
|
Timestamp      : ...
Area           : SAN
Subarea        : 00
Level          : 1
Exception      : -
CPU ID         : ..
Caller         : 0x...
Record ID      : 2
Tag            : fsscth2
Request ID     : 0x<request_id>
Destination ID : 0x00fffffc
SAN resp short : 01000000 fc020000 80010000 00090700
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
SAN resp length: 16384
San resp info  : 01000000 fc020000 80010000 00090700
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]
                 00000000 00000000 00000000 00000000 [trailing info]

The fix saves all but one of the previously associated 64 PAYload trace
record chunks of size 256 bytes each.

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Fixes: aceeffbb59bb ("zfcp: trace full payload of all SAN records (req,resp,iels)")
Fixes: 2c55b750a884 ("[SCSI] zfcp: Redesign of the debug tracing for SAN records.")
Cc: <stable@vger.kernel.org> #2.6.38+
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_dbf.c

@@ -3,7 +3,7 @@
  *
  * Debug traces for zfcp.
  *
- * Copyright IBM Corp. 2002, 2016
+ * Copyright IBM Corp. 2002, 2017
  */
 
 #define KMSG_COMPONENT "zfcp"
@@ -447,6 +447,7 @@ static u16 zfcp_dbf_san_res_cap_len_if_gpn_ft(char *tag,
 	struct fc_ct_hdr *reqh = sg_virt(ct_els->req);
 	struct fc_ns_gid_ft *reqn = (struct fc_ns_gid_ft *)(reqh + 1);
 	struct scatterlist *resp_entry = ct_els->resp;
+	struct fc_ct_hdr *resph;
 	struct fc_gpn_ft_resp *acc;
 	int max_entries, x, last = 0;
 
@@ -473,6 +474,13 @@ static u16 zfcp_dbf_san_res_cap_len_if_gpn_ft(char *tag,
 		return len; /* not GPN_FT response so do not cap */
 
 	acc = sg_virt(resp_entry);
+
+	/* cap all but accept CT responses to at least the CT header */
+	resph = (struct fc_ct_hdr *)acc;
+	if ((ct_els->status) ||
+	    (resph->ct_cmd != cpu_to_be16(FC_FS_ACC)))
+		return max(FC_CT_HDR_LEN, ZFCP_DBF_SAN_MAX_PAYLOAD);
+
 	max_entries = (reqh->ct_mr_size * 4 / sizeof(struct fc_gpn_ft_resp))
 		+ 1 /* zfcp_fc_scan_ports: bytes correct, entries off-by-one
 		     * to account for header as 1st pseudo "entry" */;

drivers/s390/scsi/zfcp_fsf.c

@@ -928,8 +928,8 @@ static void zfcp_fsf_send_ct_handler(struct zfcp_fsf_req *req)
 
 	switch (header->fsf_status) {
         case FSF_GOOD:
-		zfcp_dbf_san_res("fsscth2", req);
 		ct->status = 0;
+		zfcp_dbf_san_res("fsscth2", req);
 		break;
         case FSF_SERVICE_CLASS_NOT_SUPPORTED:
 		zfcp_fsf_class_not_supp(req);
@@ -1108,8 +1108,8 @@ static void zfcp_fsf_send_els_handler(struct zfcp_fsf_req *req)
 
 	switch (header->fsf_status) {
 	case FSF_GOOD:
-		zfcp_dbf_san_res("fsselh1", req);
 		send_els->status = 0;
+		zfcp_dbf_san_res("fsselh1", req);
 		break;
 	case FSF_SERVICE_CLASS_NOT_SUPPORTED:
 		zfcp_fsf_class_not_supp(req);