[PATCH v1 1/1] blktrace/events: Add an option to stop blktrace upon a number of events

It is useful to be able to run blktrace in a way that it stops when a
certain number of events is reached. This patch adds a new -e/--events
command line argument. Note this limit is per block device and can be
used in combination with the -w/--stopwatch argument.

Documentation is updated to include the new argument.

Signed-off-by: Stephen Bates <[email protected]>
---
 README           |  3 ++-
 blktrace.c       | 49 +++++++++++++++++++++++++++++++++++++++++++++++-
 doc/blktrace.8   | 15 +++++++++++++--
 doc/blktrace.tex |  7 ++++++-
 4 files changed, 69 insertions(+), 5 deletions(-)

diff --git a/README b/README
index d7d1fbf..7fd803b 100644
--- a/README
+++ b/README
@@ -38,7 +38,7 @@ Usage
 -----
 
 $ blktrace -d <dev> [ -r debug_path ] [ -o output ] [ -k ] [ -w time ]
-		    [ -a action ] [ -A action mask ]
+		    [ -e events] [ -a action ] [ -A action mask ]
 
 	-d Use specified device. May also be given last after options.
 	-r Path to mounted debugfs, defaults to /sys/kernel/debug.
@@ -46,6 +46,7 @@ $ blktrace -d <dev> [ -r debug_path ] [ -o output ] [ -k ] [ -w time ]
 	-D Directory to prepend to output file names.
 	-k Kill running trace.
 	-w Stop after defined time, in seconds.
+	-e Stop after defined captured trace events.
 	-a Only trace specific actions (use more -a options to add actions).
 	   Available actions are:
 
diff --git a/blktrace.c b/blktrace.c
index 038b2cb..bc3fe84 100644
--- a/blktrace.c
+++ b/blktrace.c
@@ -282,6 +282,8 @@ static int pagesize;
 static int act_mask = ~0U;
 static int kill_running_trace;
 static int stop_watch;
+static unsigned long long  events;
+static volatile int events_done;
 static int piped_output;
 
 static char *debugfs_path = "/sys/kernel/debug";
@@ -329,7 +331,7 @@ static int *cl_fds;
 static int (*handle_pfds)(struct tracer *, int, int);
 static int (*handle_list)(struct tracer_devpath_head *, struct list_head *);
 
-#define S_OPTS	"d:a:A:r:o:kw:vVb:n:D:lh:p:sI:"
+#define S_OPTS	"d:a:A:e:r:o:kw:vVb:n:D:lh:p:sI:"
 static struct option l_opts[] = {
 	{
 		.name = "dev",
@@ -355,6 +357,12 @@ static struct option l_opts[] = {
 		.flag = NULL,
 		.val = 'A'
 	},
+	{
+		.name = "events",
+		.has_arg = required_argument,
+		.flag = NULL,
+		.val = 'e'
+	},
 	{
 		.name = "relay",
 		.has_arg = required_argument,
@@ -444,6 +452,7 @@ static char usage_str[] = "\n\n" \
         "[ -o <file>          | --output=<file>]\n" \
         "[ -D <dir>           | --output-dir=<dir>\n" \
         "[ -w <time>          | --stopwatch=<time>]\n" \
+        "[ -e <events>        | --events=<number>]\n" \
         "[ -a <action field>  | --act-mask=<action field>]\n" \
         "[ -A <action mask>   | --set-mask=<action mask>]\n" \
         "[ -b <size>          | --buffer-size]\n" \
@@ -461,6 +470,7 @@ static char usage_str[] = "\n\n" \
 	"\t-o File(s) to send output to\n" \
 	"\t-D Directory to prepend to output file names\n" \
 	"\t-w Stop after defined time, in seconds\n" \
+	"\t-e Stop after defined number of trace events\n" \
 	"\t-a Only trace specified actions. See documentation\n" \
 	"\t-A Give trace mask as a single value. See documentation\n" \
 	"\t-b Sub buffer size in KiB (default 512)\n" \
@@ -1862,6 +1872,34 @@ static void *thread_main(void *arg)
 		else if (ndone < 0 && errno != EINTR)
 			fprintf(stderr, "Thread %d poll failed: %d/%s\n",
 				tp->cpu, errno, strerror(errno));
+
+		if (ndone && events) {
+			struct list_head *p;
+			unsigned long long nevents;
+
+			__list_for_each(p, &devpaths) {
+				int cpu;
+				struct pdc_stats *sp;
+				struct devpath *dpp = list_entry(p, struct devpath, head);
+				nevents = 0;
+
+				for (cpu = 0, sp = dpp->stats; cpu < dpp->ncpus; cpu++, sp++) {
+					/*
+					 * Estimate events if not known...
+					 */
+					if (sp->nevents == 0) {
+						nevents += sp->data_read /
+							sizeof(struct blk_io_trace);
+					} else
+						nevents += sp->nevents;
+
+				}
+				if (events && (nevents >= events))
+					events_done = 1;
+			}
+			if (events_done)
+				tp->is_done = 1;
+		}
 	}
 
 	/*
@@ -2155,6 +2193,15 @@ static int handle_args(int argc, char *argv[])
 			break;
 		}
 
+		case 'e':
+			events = strtoull(optarg, NULL, 10);
+			if (events == 0) {
+				fprintf(stderr,
+					"Invalid events value (%llu)\n",
+					events);
+				return 1;
+			}
+			break;
 		case 'r':
 			debugfs_path = optarg;
 			break;
diff --git a/doc/blktrace.8 b/doc/blktrace.8
index 820b03a..b32cede 100644
--- a/doc/blktrace.8
+++ b/doc/blktrace.8
@@ -6,7 +6,7 @@ blktrace \- generate traces of the i/o traffic on block devices
 
 
 .SH SYNOPSIS
-.B blktrace \-d \fIdev\fR [ \-r \fIdebugfs_path\fR ] [ \-o \fIoutput\fR ] [ \-w \fItime\fR ] [ \-a \fIaction\fR ] [ \-A \fIaction_mask\fR ] [ \-v ]
+.B blktrace \-d \fIdev\fR [ \-r \fIdebugfs_path\fR ] [ \-o \fIoutput\fR ] [ \-w \fItime\fR ] [ \-e \fIevents\fR ] [ \-a \fIaction\fR ] [ \-A \fIaction_mask\fR ] [ \-v ]
 .br
 
 
@@ -69,7 +69,11 @@ The default behaviour for blktrace is to run forever until explicitly
 killed by the user (via a control-C, or sending SIGINT signal to the
 process via invocation the kill (1) utility). Also you can specify a
 run-time duration for blktrace via the \fB\-w\fR option -- then
-blktrace will run for the specified number of seconds, and then halt.
+blktrace will run for the specified number of seconds, and then
+halt. Or you can specify a number of records to capture via the
+\fB-e\fR option. Note that this will cause blktrace to stop when the
+first block device reaches this. The \fB-w\fR and \fB-e\fR options can
+be combined with the first one to be reached taking prescident.
 
 
 .SH OPTIONS
@@ -191,6 +195,13 @@ Outputs version
 Sets run time to the number of seconds specified  
 .RE
 
+\-e \fIevents\fR
+.br
+\-\-events=\fIevents\fR
+.RS
+Sets run to stop when the specifed number of events are captured for any one block device
+.RE
+
 
 .SH FILTER MASKS
 The following masks may be passed with the \fI\-a\fR command line
diff --git a/doc/blktrace.tex b/doc/blktrace.tex
index 836ac4a..d78de8b 100644
--- a/doc/blktrace.tex
+++ b/doc/blktrace.tex
@@ -377,7 +377,12 @@ of the more arcane command line options:
     \item You can specify a run-time duration for blktrace via the
     \emph{-w} option -- then blktrace will run for the specified number
     of seconds, and then halt.
-  \end{enumerate}
+
+    \item You can specify a record entry duration for blktrace via the
+    \emph{-e} option -- then blktrace will run until the specified
+    number of records are captured for any of the block devices, and
+    then halt.
+\end{enumerate}
 \end{itemize}
 
 \subsection{\label{sec:blktrace-args}Command line arguments}
-- 
2.43.0