[v4,1/3] trace-cmd: Make read_proc() to return int status via OUT arg
diff mbox series

Message ID 20180116195343.12800-2-vladislav.valtchev@gmail.com
State New, archived
Headers show
Series
  • Integrate stack tracer status in 'stat'
Related show

Commit Message

Vladislav Valtchev (VMware) Jan. 16, 2018, 7:53 p.m. UTC
This patch changes both the implementation and the interface of read_proc()
in trace-stack.c. First, it makes the function to read a string from the proc
file and then parse it as an integer using strtol(). Then, it makes the function
to return the integer read from the proc file using the int *status OUT
parameter, in order to make possible its return value to be used by the caller
to check if the operation succeeded.

This new implementation relaxes the external contraints the function relies on,
making it possible to be used by trace stat. The point is that 'stat' should not
fail in case there is something wrong with the stack tracer. Only the call to
die() in case the file is empty has been left in this patch: it will be removed
as well in a separate commit.

Signed-off-by: Vladislav Valtchev (VMware) <vladislav.valtchev@gmail.com>
---
 trace-stack.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 57 insertions(+), 15 deletions(-)

Comments

Steven Rostedt Jan. 19, 2018, 9:58 p.m. UTC | #1
Just to let you know. I accepted all three of your patches. I have one
comment, (and changed this myself).

On Tue, 16 Jan 2018 21:53:41 +0200
"Vladislav Valtchev (VMware)" <vladislav.valtchev@gmail.com> wrote:

> file and then parse it as an integer using strtol(). Then, it makes the function

This line is 80 characters. For commit logs, we recommend no more than
76 characters (some people suggest 74). The reason is that a git show
will add 4 characters, to each line of the log, and this will cause an
overflow like this:

commit 68f00f512883fa7f1d04a7d88defff5e687bd98f
Author: Vladislav Valtchev (VMware) <vladislav.valtchev@gmail.com>
Date:   Tue Jan 16 21:53:41 2018 +0200

    trace-cmd: Make read_proc() to return int status via OUT arg

    This patch changes both the implementation and the interface of read_proc()
    in trace-stack.c. First, it makes the function to read a string from the pro
c
    file and then parse it as an integer using strtol(). Then, it makes the func
tion
    to return the integer read from the proc file using the int *status OUT
    parameter, in order to make possible its return value to be used by the call
er
    to check if the operation succeeded.

    This new implementation relaxes the external contraints the function relies
on,
    making it possible to be used by trace stat. The point is that 'stat' should
 not
    fail in case there is something wrong with the stack tracer. Only the call t
o
    die() in case the file is empty has been left in this patch: it will be remo
ved
    as well in a separate commit.


When editing a git log with the vim editor, I usually do :set tw=76

Thanks!

-- Steve
Steven Rostedt Jan. 19, 2018, 10:02 p.m. UTC | #2
On Fri, 19 Jan 2018 16:58:02 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> Just to let you know. I accepted all three of your patches. I have one
> comment, (and changed this myself).

Anyway,

Great job so far! I think I'm all set to start getting trace-cmd 2.7
out now. Unfortunately, I don't think I'll be able to get to that
before I leave on my next trip.

-- Steve
Vladislav Valtchev (VMware) Jan. 22, 2018, 9:03 a.m. UTC | #3
On Fri, 2018-01-19 at 17:02 -0500, Steven Rostedt wrote:
> On Fri, 19 Jan 2018 16:58:02 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > Just to let you know. I accepted all three of your patches. I have one
> > comment, (and changed this myself).
> 
> Anyway,
> 
> Great job so far! I think I'm all set to start getting trace-cmd 2.7
> out now. Unfortunately, I don't think I'll be able to get to that
> before I leave on my next trip.
> 
> -- Steve


Thanks Steven, I'm happy that you accepted my patches!
Sure, the next time I'll use 76 (or maybe even 74) as col limit
for the description.

Patch
diff mbox series

diff --git a/trace-stack.c b/trace-stack.c
index aa79ae3..fada62d 100644
--- a/trace-stack.c
+++ b/trace-stack.c
@@ -20,6 +20,7 @@ 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <limits.h>
 #include <getopt.h>
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -49,37 +50,74 @@  static void test_available(void)
 		die("stack tracer not configured on running kernel");
 }
 
-static char read_proc(void)
+/*
+ * Returns:
+ *   -1 - Something went wrong
+ *    0 - File does not exist (stack tracer not enabled)
+ *    1 - Success
+ */
+static int read_proc(int *status)
 {
-	char buf[1];
+	struct stat stat_buf;
+	char buf[64];
+	long num;
 	int fd;
 	int n;
 
+	if (stat(PROC_FILE, &stat_buf) < 0) {
+		/* stack tracer not configured on running kernel */
+		*status = 0; /* not configured means disabled */
+		return 0;
+	}
+
 	fd = open(PROC_FILE, O_RDONLY);
+
 	if (fd < 0)
-		die("reading %s", PROC_FILE);
-	n = read(fd, buf, 1);
+		return -1;
+
+	n = read(fd, buf, sizeof(buf));
 	close(fd);
-	if (n != 1)
+
+	if (n <= 0)
 		die("error reading %s", PROC_FILE);
 
-	return buf[0];
+	if (n >= sizeof(buf))
+		return -1;
+
+	buf[n] = 0;
+	errno = 0;
+	num = strtol(buf, NULL, 10);
+
+	/* Check for various possible errors */
+	if (num > INT_MAX || num < INT_MIN || (!num && errno))
+		return -1;
+
+	*status = num;
+	return 1; /* full success */
 }
 
-static void start_stop_trace(char val)
+/* NOTE: this implementation only accepts new_status in the range [0..9]. */
+static void change_stack_tracer_status(unsigned new_status)
 {
 	char buf[1];
+	int status;
 	int fd;
 	int n;
 
-	buf[0] = read_proc();
-	if (buf[0] == val)
+	if (new_status > 9) {
+		warning("invalid status %d\n", new_status);
 		return;
+	}
+
+	if (read_proc(&status) > 0 && status == new_status)
+		return; /* nothing to do */
 
 	fd = open(PROC_FILE, O_WRONLY);
 	if (fd < 0)
 		die("writing %s", PROC_FILE);
-	buf[0] = val;
+
+	buf[0] = new_status + '0';
+
 	n = write(fd, buf, 1);
 	if (n < 0)
 		die("writing into %s", PROC_FILE);
@@ -88,12 +126,12 @@  static void start_stop_trace(char val)
 
 static void start_trace(void)
 {
-	start_stop_trace('1');
+	change_stack_tracer_status(1);
 }
 
 static void stop_trace(void)
 {
-	start_stop_trace('0');
+	change_stack_tracer_status(0);
 }
 
 static void reset_trace(void)
@@ -118,13 +156,17 @@  static void reset_trace(void)
 
 static void read_trace(void)
 {
-	FILE *fp;
-	char *path;
 	char *buf = NULL;
+	int status;
+	char *path;
+	FILE *fp;
 	size_t n;
 	int r;
 
-	if (read_proc() == '1')
+	if (read_proc(&status) <= 0)
+		die("Invalid stack tracer state");
+
+	if (status > 0)
 		printf("(stack tracer running)\n");
 	else
 		printf("(stack tracer not running)\n");