perf: Robustify proc and debugfs file recording

While attempting to create a timechart of boot up I found perf didn't
tolerate modules being loaded/unloaded.  This patch fixes this by
reading the file once and then writing the size read at the correct
point in the file.  It also simplifies the code somewhat.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Link: http://lkml.kernel.org/r/10011.1310614483@neuling.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/perf/util/trace-event-info.c

@@ -183,106 +183,59 @@ int bigendian(void)
 	return *ptr == 0x01020304;
 }
 
-static unsigned long long copy_file_fd(int fd)
+/* unfortunately, you can not stat debugfs or proc files for size */
+static void record_file(const char *file, size_t hdr_sz)
 {
 	unsigned long long size = 0;
-	char buf[BUFSIZ];
-	int r;
-
-	do {
-		r = read(fd, buf, BUFSIZ);
-		if (r > 0) {
-			size += r;
-			write_or_die(buf, r);
-		}
-	} while (r > 0);
-
-	return size;
-}
-
-static unsigned long long copy_file(const char *file)
-{
-	unsigned long long size = 0;
-	int fd;
+	char buf[BUFSIZ], *sizep;
+	off_t hdr_pos = lseek(output_fd, 0, SEEK_CUR);
+	int r, fd;
 
 	fd = open(file, O_RDONLY);
 	if (fd < 0)
 		die("Can't read '%s'", file);
-	size = copy_file_fd(fd);
-	close(fd);
 
-	return size;
-}
-
-static unsigned long get_size_fd(int fd)
-{
-	unsigned long long size = 0;
-	char buf[BUFSIZ];
-	int r;
+	/* put in zeros for file size, then fill true size later */
+	write_or_die(&size, hdr_sz);
 
 	do {
 		r = read(fd, buf, BUFSIZ);
-		if (r > 0)
+		if (r > 0) {
 			size += r;
+			write_or_die(buf, r);
+		}
 	} while (r > 0);
-
-	lseek(fd, 0, SEEK_SET);
-
-	return size;
-}
-
-static unsigned long get_size(const char *file)
-{
-	unsigned long long size = 0;
-	int fd;
-
-	fd = open(file, O_RDONLY);
-	if (fd < 0)
-		die("Can't read '%s'", file);
-	size = get_size_fd(fd);
 	close(fd);
 
-	return size;
+	/* ugh, handle big-endian hdr_size == 4 */
+	sizep = (char*)&size;
+	if (bigendian())
+		sizep += sizeof(u64) - hdr_sz;
+
+	if (pwrite(output_fd, sizep, hdr_sz, hdr_pos) < 0)
+		die("writing to %s", output_file);
 }
 
 static void read_header_files(void)
 {
-	unsigned long long size, check_size;
 	char *path;
-	int fd;
+	struct stat st;
 
 	path = get_tracing_file("events/header_page");
-	fd = open(path, O_RDONLY);
-	if (fd < 0)
+	if (stat(path, &st) < 0)
 		die("can't read '%s'", path);
 
-	/* unfortunately, you can not stat debugfs files for size */
-	size = get_size_fd(fd);
-
 	write_or_die("header_page", 12);
-	write_or_die(&size, 8);
-	check_size = copy_file_fd(fd);
-	close(fd);
-
-	if (size != check_size)
-		die("wrong size for '%s' size=%lld read=%lld",
-		    path, size, check_size);
+	record_file(path, 8);
 	put_tracing_file(path);
 
 	path = get_tracing_file("events/header_event");
-	fd = open(path, O_RDONLY);
-	if (fd < 0)
+	if (stat(path, &st) < 0)
 		die("can't read '%s'", path);
 
-	size = get_size_fd(fd);
-
 	write_or_die("header_event", 13);
-	write_or_die(&size, 8);
-	check_size = copy_file_fd(fd);
-	if (size != check_size)
-		die("wrong size for '%s'", path);
+	record_file(path, 8);
 	put_tracing_file(path);
-	close(fd);
 }
 
 static bool name_in_tp_list(char *sys, struct tracepoint_path *tps)
@@ -298,7 +251,6 @@ static bool name_in_tp_list(char *sys, struct tracepoint_path *tps)
 
 static void copy_event_system(const char *sys, struct tracepoint_path *tps)
 {
-	unsigned long long size, check_size;
 	struct dirent *dent;
 	struct stat st;
 	char *format;
@@ -338,14 +290,8 @@ static void copy_event_system(const char *sys, struct tracepoint_path *tps)
 		sprintf(format, "%s/%s/format", sys, dent->d_name);
 		ret = stat(format, &st);
 
-		if (ret >= 0) {
-			/* unfortunately, you can not stat debugfs files for size */
-			size = get_size(format);
-			write_or_die(&size, 8);
-			check_size = copy_file(format);
-			if (size != check_size)
-				die("error in size of file '%s'", format);
-		}
+		if (ret >= 0)
+			record_file(format, 8);
 
 		free(format);
 	}
@@ -426,7 +372,7 @@ static void read_event_files(struct tracepoint_path *tps)
 
 static void read_proc_kallsyms(void)
 {
-	unsigned int size, check_size;
+	unsigned int size;
 	const char *path = "/proc/kallsyms";
 	struct stat st;
 	int ret;
@@ -438,17 +384,12 @@ static void read_proc_kallsyms(void)
 		write_or_die(&size, 4);
 		return;
 	}
-	size = get_size(path);
-	write_or_die(&size, 4);
-	check_size = copy_file(path);
-	if (size != check_size)
-		die("error in size of file '%s'", path);
-
+	record_file(path, 4);
 }
 
 static void read_ftrace_printk(void)
 {
-	unsigned int size, check_size;
+	unsigned int size;
 	char *path;
 	struct stat st;
 	int ret;
@@ -461,11 +402,8 @@ static void read_ftrace_printk(void)
 		write_or_die(&size, 4);
 		goto out;
 	}
-	size = get_size(path);
-	write_or_die(&size, 4);
-	check_size = copy_file(path);
-	if (size != check_size)
-		die("error in size of file '%s'", path);
+	record_file(path, 4);
+
 out:
 	put_tracing_file(path);
 }