PATCH udev-106 /proc/stat buffer to small

I am assuming that this is the correct place to post udev patches for consideration, feel free to inform me otherwise :-).

George

This came up on a system with 1024cores (well 768cpus and 256 hyper-threads) where the buffer size for reading /proc/stat was not large enough causing udev to fail during the boot process. The read_proc_stat(void) eliminates this problem.

routine makes sure that the

@@ -357,25 +357,58 @@
 	return memsize / 1024;
 }
 
-static int cpu_count(void)
+/*
+ * Use the same buffer for cpu_count() and running_processes()
+ */
+
+static char* stat_buf = NULL;
+static int   stat_buf_size = 4096;
+
+static int read_proc_stat(void)
 {
 	int f;
-	char buf[32768];
 	int len;
-	const char *pos;
-	int count = 0;
 
-	f = open("/proc/stat", O_RDONLY);
-	if (f == -1)
-		return -1;
+	if (stat_buf == NULL) {
+		stat_buf = malloc(stat_buf_size);
+		if (stat_buf == NULL)
+			return -1;
+	}
 
-	len = read(f, buf, sizeof(buf)-1);
+	do {
+		f = open("/proc/stat", O_RDONLY);
+		if (f == -1)
+			return -1;
+
+		len = read(f, stat_buf, stat_buf_size-1);
+		if (len < stat_buf_size-1)
+			break;
+
+		stat_buf_size *= 2;
+		stat_buf = realloc(stat_buf, stat_buf_size);
+		if (stat_buf == NULL)
+			return -1;
+	} while (1);
 	close(f);
+
 	if (len <= 0)
 		return -1;
-	buf[len] = '\0';
+	stat_buf[len] = '\0';
+	return len;
+}
+
 
-	pos = strstr(buf, "cpu");
+static int cpu_count(void)
+{
+	int len;
+	const char *pos;
+	int count = 0;
+
+	len = read_proc_stat();
+	if (len <= 0)
+		return -1;
+
+	pos = strstr(stat_buf, "cpu");
 	if (pos == NULL)
 		return -1;
 

@@ -392,23 +425,15 @@
 
 static int running_processes(void)
 {
-	int f;
-	char buf[32768];
 	int len;
 	int running;
 	const char *pos;
 
-	f = open("/proc/stat", O_RDONLY);
-	if (f == -1)
-		return -1;
-
-	len = read(f, buf, sizeof(buf)-1);
-	close(f);
+	len = read_proc_stat();
 	if (len <= 0)
 		return -1;
-	buf[len] = '\0';
 
-	pos = strstr(buf, "procs_running ");
+	pos = strstr(stat_buf, "procs_running ");
 	if (pos == NULL)
 		return -1;
 

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sigh...

Never answer the phone in the middle of preparing a post :-( s/to/too/ is subject

Delete:

The actual patch should be good :-).

George

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"fail"? What fails? How? It should still find hundreds of your CPU's, right?

Just curious, what size is the content of /proc/stat on this box?

Thanks,
Kay

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First, I will post an improved patch as I completely forgot udev was threaded (duh..).

Yes and no as it turns out because udev also looks at procs_running which is at
the end of the list. If the buffer isn't big enough it returns an error, does a lame
boot, and puts FAILED rather than OK in the syslog.

Aprox 48000 is my memory -- well above the 32768 that the buffer size was. Really want this to scale to 4k or so without doing anything terrible to the 1p 128meg systems that still exist.

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Threaded?

Well, I rather switch to fgets(), that should leave all that buffered IO crap to glibc. As we are reading a seq proc-file here, it doesn't really make sense to put the whole file into a local buffer before reading it, right?

Thanks,
Kay

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