[PATCH v4 14/22] sg: rework debug info

[Douglas Gilbert <dgilbert@interlog.com>]

Since the version 2 driver, the state of the driver can be found
with 'cat /proc/scsi/sg/debug'. As the driver becomes more
threaded and IO faster (e.g. scsi_debug with a command timer
of 5 microseconds), the existing state dump can become
misleading as the state can change during the "snapshot". The
new approach in this patch is to allocate a buffer of
SG_PROC_DEBUG_SZ bytes and use scnprintf() to populate it. Only
when the whole state is captured (or the buffer fills) is the
output to the caller's terminal performed. The previous
approach was line based: assemble a line of information and
then output it.

Locks are taken as required for short periods and should not
interfere with a disk IO intensive program. Operations
such as closing a sg file descriptor or removing a sg device
may be held up for a short while (microseconds).

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/sg.c | 235 +++++++++++++++++++++++++++++++---------------
 1 file changed, 157 insertions(+), 78 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 3da326677de4..79eb9089dc2c 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -3769,115 +3769,194 @@ sg_proc_seq_show_devstrs(struct seq_file *s, void *v)
 	return 0;
 }
 
-/* must be called while holding sg_index_lock */
-static void
-sg_proc_debug_helper(struct seq_file *s, struct sg_device *sdp)
+/* Writes debug info for one sg_request in obp buffer */
+static int
+sg_proc_debug_sreq(struct sg_request *srp, int to, char *obp, int len)
 {
-	int k;
+	bool is_v3v4, v4, is_dur;
+	int n = 0;
+	u32 dur;
+	enum sg_rq_state rq_st;
+	const char *cp;
+
+	if (len < 1)
+		return 0;
+	v4 = test_bit(SG_FRQ_IS_V4I, srp->frq_bm);
+	is_v3v4 = v4 ? true : (srp->s_hdr3.interface_id != '\0');
+	if (srp->parentfp->rsv_srp == srp)
+		cp = (is_v3v4 && (srp->rq_flags & SG_FLAG_MMAP_IO)) ?
+				"     mmap>> " : "     rsv>> ";
+	else
+		cp = (srp->rq_info & SG_INFO_DIRECT_IO_MASK) ?
+				"     dio>> " : "     ";
+	rq_st = atomic_read(&srp->rq_st);
+	dur = sg_get_dur(srp, &rq_st, &is_dur);
+	n += scnprintf(obp + n, len - n, "%s%s: dlen=%d/%d id=%d", cp,
+		       sg_rq_st_str(rq_st, false), srp->sgat_h.dlen,
+		       srp->sgat_h.buflen, (int)srp->pack_id);
+	if (is_dur)	/* cmd/req has completed, waiting for ... */
+		n += scnprintf(obp + n, len - n, " dur=%ums", dur);
+	else if (dur < U32_MAX)	/* in-flight or busy (so ongoing) */
+		n += scnprintf(obp + n, len - n, " t_o/elap=%us/%ums",
+			       to / 1000, dur);
+	n += scnprintf(obp + n, len - n, " sgat=%d op=0x%02x\n",
+		       srp->sgat_h.num_sgat, srp->cmd_opcode);
+	return n;
+}
+
+/* Writes debug info for one sg fd (including its sg requests) in obp buffer */
+static int
+sg_proc_debug_fd(struct sg_fd *fp, char *obp, int len)
+{
+	bool first_fl;
+	int n = 0;
+	int to;
 	struct sg_request *srp;
-	struct sg_fd *fp;
-	const char * cp;
-	unsigned int ms;
 
-	k = 0;
-	list_for_each_entry(fp, &sdp->sfds, sfd_entry) {
-		k++;
-		spin_lock(&fp->rq_list_lock); /* irqs already disabled */
-		seq_printf(s, "   FD(%d): timeout=%dms bufflen=%d "
-			   "(res)sgat=%d low_dma=%d\n", k,
-			   jiffies_to_msecs(fp->timeout),
-			   fp->rsv_srp->sgat_h.buflen,
-			   (int)fp->rsv_srp->sgat_h.num_sgat,
-			   (int) sdp->device->host->unchecked_isa_dma);
-		seq_printf(s, "   cmd_q=%d f_packid=%d k_orphan=%d closed=0\n",
-			   (int)test_bit(SG_FFD_CMD_Q, fp->ffd_bm),
-			   (int)test_bit(SG_FFD_FORCE_PACKID, fp->ffd_bm),
-			   (int)test_bit(SG_FFD_KEEP_ORPHAN, fp->ffd_bm));
-		seq_printf(s, "   submitted=%d waiting=%d\n",
-			   atomic_read(&fp->submitted),
-			   atomic_read(&fp->waiting));
-		list_for_each_entry(srp, &fp->rq_list, rq_entry) {
-			const struct sg_slice_hdr3 *sh3p = &srp->s_hdr3;
-			bool is_v3 = (sh3p->interface_id != '\0');
-			enum sg_rq_state rq_st = atomic_read(&srp->rq_st);
-
-			if (srp->parentfp->rsv_srp == srp) {
-				if (is_v3 && (SG_FLAG_MMAP_IO & sh3p->flags))
-					cp = "     mmap>> ";
-				else
-					cp = "     rb>> ";
-			} else {
-				if (SG_INFO_DIRECT_IO_MASK & srp->rq_info)
-					cp = "     dio>> ";
-				else
-					cp = "     ";
-			}
-			seq_puts(s, cp);
-			seq_puts(s, sg_rq_st_str(rq_st, false));
-			seq_printf(s, ": id=%d len/blen=%d/%d",
-				   srp->pack_id, srp->sgat_h.dlen,
-				   srp->sgat_h.buflen);
-			if (rq_st == SG_RS_AWAIT_RD || rq_st == SG_RS_DONE_RD) {
-				seq_printf(s, " dur=%d", srp->duration);
-				goto fin_line;
-			}
-			ms = jiffies_to_msecs(jiffies);
-			seq_printf(s, " t_o/elap=%d/%d",
-				   (is_v3 ? sh3p->timeout :
-					    jiffies_to_msecs(fp->timeout)),
-				   (ms > srp->duration ?  ms - srp->duration :
-							  0));
-fin_line:
-			seq_printf(s, "ms sgat=%d op=0x%02x\n",
-				   srp->sgat_h.num_sgat, (int)srp->cmd_opcode);
+	/* sgat=-1 means unavailable */
+	to = jiffies_to_msecs(fp->timeout);
+	if (to % 1000)
+		n += scnprintf(obp + n, len - n, "timeout=%dms rs", to);
+	else
+		n += scnprintf(obp + n, len - n, "timeout=%ds rs", to / 1000);
+	n += scnprintf(obp + n, len - n, "v_buflen=%d\n   cmd_q=%d ",
+		       fp->rsv_srp->sgat_h.buflen,
+		       (int)test_bit(SG_FFD_CMD_Q, fp->ffd_bm));
+	n += scnprintf(obp + n, len - n,
+		       "f_packid=%d k_orphan=%d ffd_bm=0x%lx\n",
+		       (int)test_bit(SG_FFD_FORCE_PACKID, fp->ffd_bm),
+		       (int)test_bit(SG_FFD_KEEP_ORPHAN, fp->ffd_bm),
+		       fp->ffd_bm[0]);
+	n += scnprintf(obp + n, len - n, "   mmap_called=%d\n",
+		       test_bit(SG_FFD_MMAP_CALLED, fp->ffd_bm));
+	n += scnprintf(obp + n, len - n,
+		       "   submitted=%d waiting=%d   open thr_id=%d\n",
+		       atomic_read(&fp->submitted),
+		       atomic_read(&fp->waiting), fp->tid);
+	list_for_each_entry_rcu(srp, &fp->rq_list, rq_entry) {
+		spin_lock(&srp->req_lck);
+		n += sg_proc_debug_sreq(srp, fp->timeout, obp + n, len - n);
+		spin_unlock(&srp->req_lck);
+	}
+	if (list_empty(&fp->rq_list))
+		n += scnprintf(obp + n, len - n, "     No requests active\n");
+	first_fl = true;
+	list_for_each_entry_rcu(srp, &fp->rq_fl, fl_entry) {
+		if (first_fl) {
+			n += scnprintf(obp + n, len - n, "   Free list:\n");
+			first_fl = false;
 		}
-		if (list_empty(&fp->rq_list))
-			seq_puts(s, "     No requests active\n");
-		spin_unlock(&fp->rq_list_lock);
+		spin_lock(&srp->req_lck);
+		n += sg_proc_debug_sreq(srp, fp->timeout, obp + n, len - n);
+		spin_unlock(&srp->req_lck);
+	}
+	return n;
+}
+
+/* Writes debug info for one sg device (including its sg fds) in obp buffer */
+static int
+sg_proc_debug_sdev(struct sg_device *sdp, char *obp, int len, int *fd_counterp)
+{
+	int n = 0;
+	int my_count = 0;
+	struct scsi_device *ssdp = sdp->device;
+	struct sg_fd *fp;
+	char *disk_name;
+	int *countp;
+
+	countp = fd_counterp ? fd_counterp : &my_count;
+	disk_name = (sdp->disk ? sdp->disk->disk_name : "?_?");
+	n += scnprintf(obp + n, len - n, " >>> device=%s ", disk_name);
+	n += scnprintf(obp + n, len - n, "%d:%d:%d:%llu ", ssdp->host->host_no,
+		       ssdp->channel, ssdp->id, ssdp->lun);
+	n += scnprintf(obp + n, len - n,
+		       "  max_sgat_sz,elems=2^%d,%d excl=%d open_cnt=%d\n",
+		       ilog2(sdp->max_sgat_sz), sdp->max_sgat_elems,
+		       SG_HAVE_EXCLUDE(sdp), atomic_read(&sdp->open_cnt));
+	list_for_each_entry(fp, &sdp->sfds, sfd_entry) {
+		++*countp;
+		rcu_read_lock(); /* assume irqs disabled */
+		n += scnprintf(obp + n, len - n, "  FD(%d): ", *countp);
+		n += sg_proc_debug_fd(fp, obp + n, len - n);
+		rcu_read_unlock();
 	}
+	return n;
 }
 
+/* Called via dbg_seq_ops once for each sg device */
 static int
 sg_proc_seq_show_debug(struct seq_file *s, void *v)
 {
+	bool found = false;
+	bool trunc = false;
+	const int bp_len = SG_PROC_DEBUG_SZ;
+	int n = 0;
+	int k = 0;
+	unsigned long iflags;
 	struct sg_proc_deviter *it = (struct sg_proc_deviter *)v;
 	struct sg_device *sdp;
-	unsigned long iflags;
+	int *fdi_p;
+	char *bp;
+	char *disk_name;
+	char b1[128];
 
+	b1[0] = '\0';
 	if (it && (0 == it->index))
 		seq_printf(s, "max_active_device=%d  def_reserved_size=%d\n",
-			   (int)it->max, sg_big_buff);
-
+			   (int)it->max, def_reserved_size);
+	fdi_p = it ? &it->fd_index : &k;
+	bp = kzalloc(bp_len, __GFP_NOWARN | GFP_KERNEL);
+	if (!bp) {
+		seq_printf(s, "%s: Unable to allocate %d on heap, finish\n",
+			   __func__, bp_len);
+		return -1;
+	}
 	read_lock_irqsave(&sg_index_lock, iflags);
 	sdp = it ? sg_lookup_dev(it->index) : NULL;
 	if (NULL == sdp)
 		goto skip;
 	read_lock(&sdp->sfd_lock);
 	if (!list_empty(&sdp->sfds)) {
-		seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
+		found = true;
+		disk_name = (sdp->disk ? sdp->disk->disk_name : "?_?");
 		if (SG_IS_DETACHING(sdp))
-			seq_puts(s, "detaching pending close ");
+			snprintf(b1, sizeof(b1), " >>> device=%s  %s\n",
+				 disk_name, "detaching pending close\n");
 		else if (sdp->device) {
-			struct scsi_device *scsidp = sdp->device;
-
-			seq_printf(s, "%d:%d:%d:%llu   em=%d",
-				   scsidp->host->host_no,
-				   scsidp->channel, scsidp->id,
-				   scsidp->lun,
-				   scsidp->host->hostt->emulated);
+			n = sg_proc_debug_sdev(sdp, bp, bp_len, fdi_p);
+			if (n >= bp_len - 1) {
+				trunc = true;
+				if (bp[bp_len - 2] != '\n')
+					bp[bp_len - 2] = '\n';
+			}
+		} else {
+			snprintf(b1, sizeof(b1), " >>> device=%s  %s\n",
+				 disk_name, "sdp->device==NULL, skip");
 		}
-		seq_printf(s, " max_sgat_elems=%d excl=%d open_cnt=%d\n",
-			   sdp->max_sgat_elems, SG_HAVE_EXCLUDE(sdp),
-			   atomic_read(&sdp->open_cnt));
-		sg_proc_debug_helper(s, sdp);
 	}
 	read_unlock(&sdp->sfd_lock);
 skip:
 	read_unlock_irqrestore(&sg_index_lock, iflags);
+	if (found) {
+		if (n > 0) {
+			seq_puts(s, bp);
+			if (seq_has_overflowed(s))
+				goto s_ovfl;
+			if (trunc)
+				seq_printf(s, "   >> Output truncated %s\n",
+					   "due to buffer size");
+		} else if (b1[0]) {
+			seq_puts(s, b1);
+			if (seq_has_overflowed(s))
+				goto s_ovfl;
+		}
+	}
+s_ovfl:
+	kfree(bp);
 	return 0;
 }
 
-#endif				/* CONFIG_SCSI_PROC_FS (~300 lines back) */
+#endif				/* CONFIG_SCSI_PROC_FS (~400 lines back) */
 
 module_init(init_sg);
 module_exit(exit_sg);
-- 
2.23.0