[PATCH 2/3] trace-cmd: Remove error processing from write_file() use error_log instead

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

When write_file() fails to write the contents given to it, it reads the file
it tried to write to and prints that. This doesn't work for all intsance
files, and newer kernels now have an "error_log" that is written to when
something fails.

Move the processing of reading the file out of write_file() and check if
error_log exists, and read from that when possible, and then default back to
the file if error_log does not exist.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 tracecmd/trace-record.c | 135 +++++++++++++++++++++++++++++++++-------
 1 file changed, 114 insertions(+), 21 deletions(-)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index efa7f8787bb7..bfe4f7976cc2 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -790,28 +790,16 @@ static int set_ftrace(int set, int use_proc)
 	return 0;
 }
 
-static int write_file(const char *file, const char *str, const char *type)
+static int write_file(const char *file, const char *str)
 {
-	char buf[BUFSIZ];
-	int fd;
 	int ret;
+	int fd;
 
 	fd = open(file, O_WRONLY | O_TRUNC);
 	if (fd < 0)
 		die("opening to '%s'", file);
 	ret = write(fd, str, strlen(str));
 	close(fd);
-	if (ret < 0 && type) {
-		/* write failed */
-		fd = open(file, O_RDONLY);
-		if (fd < 0)
-			die("writing to '%s'", file);
-		/* the filter has the error */
-		while ((ret = read(fd, buf, BUFSIZ)) > 0)
-			fprintf(stderr, "%.*s", ret, buf);
-		die("Failed %s of %s\n", type, file);
-		close(fd);
-	}
 	return ret;
 }
 
@@ -1949,9 +1937,112 @@ static int find_trigger(const char *file, char *buf, int size, int fields)
 	return len;
 }
 
+static char *read_file(const char *file)
+{
+	char stbuf[BUFSIZ];
+	char *buf = NULL;
+	int size = 0;
+	char *nbuf;
+	int fd;
+	int r;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+
+	do {
+		r = read(fd, stbuf, BUFSIZ);
+		if (r <= 0)
+			continue;
+		nbuf = realloc(buf, size+r+1);
+		if (!nbuf) {
+			free(buf);
+			buf = NULL;
+			break;
+		}
+		buf = nbuf;
+		memcpy(buf+size, stbuf, r);
+		size += r;
+	} while (r > 0);
+
+	close(fd);
+	if (r == 0 && size > 0)
+		buf[size] = '\0';
+
+	return buf;
+}
+
+static void read_error_log(const char *log)
+{
+	char *buf, *line;
+	char *start = NULL;
+	char *p;
+
+	buf = read_file(log);
+	if (!buf)
+		return;
+
+	line = buf;
+
+	/* Only the last lines have meaning */
+	while ((p = strstr(line, "\n")) && p[1]) {
+		if (line[0] != ' ')
+			start = line;
+		line = p + 1;
+	}
+
+	if (start)
+		printf("%s", start);
+
+	free(buf);
+}
+
+static void show_error(const char *file, const char *type)
+{
+	struct stat st;
+	char *path = strdup(file);
+	char *p;
+	int ret;
+
+	if (!path)
+		die("Could not allocate memory");
+
+	p = strstr(path, "tracing");
+	if (p) {
+		if (strncmp(p + sizeof("tracing"), "instances", sizeof("instances") - 1) == 0) {
+			p = strstr(p + sizeof("tracing") + sizeof("instances"), "/");
+			if (!p)
+				goto read_file;
+		} else {
+			p += sizeof("tracing") - 1;
+		}
+		ret = asprintf(&p, "%.*s/error_log", (int)(p - path), path);
+		if (ret < 0)
+			die("Could not allocate memory");
+		ret = stat(p, &st);
+		if (ret < 0) {
+			free(p);
+			goto read_file;
+		}
+		read_error_log(p);
+		goto out;
+	}
+
+ read_file:
+	p = read_file(path);
+	if (p)
+		printf("%s", p);
+
+ out:
+	printf("Failed %s of %s\n", type, file);
+	free(path);
+	return;
+}
+
 static void write_filter(const char *file, const char *filter)
 {
-	write_file(file, filter, "filter");
+	if (write_file(file, filter) < 0)
+		show_error(file, "filter");
 }
 
 static void clear_filter(const char *file)
@@ -1961,12 +2052,14 @@ static void clear_filter(const char *file)
 
 static void write_trigger(const char *file, const char *trigger)
 {
-	write_file(file, trigger, "trigger");
+	if (write_file(file, trigger) < 0)
+		show_error(file, "trigger");
 }
 
 static void write_func_filter(const char *file, const char *trigger)
 {
-	write_file(file, trigger, "function filter");
+	if (write_file(file, trigger) < 0)
+		show_error(file, "function filter");
 }
 
 static void clear_trigger(const char *file)
@@ -2059,7 +2152,7 @@ static void update_reset_files(void)
 		reset_files = reset->next;
 
 		if (!keep)
-			write_file(reset->path, reset->reset, "reset");
+			write_file(reset->path, reset->reset);
 		free(reset->path);
 		free(reset->reset);
 		free(reset);
@@ -4193,7 +4286,7 @@ static unsigned long long find_time_stamp(struct tep_handle *tep)
 }
 
 
-static char *read_file(char *file, int *psize)
+static char *read_top_file(char *file, int *psize)
 {
 	return tracefs_instance_file_read(top_instance.tracefs, file, psize);
 }
@@ -4231,7 +4324,7 @@ static char *get_date_to_ts(void)
 
 	tep_set_file_bigendian(tep, tracecmd_host_bigendian());
 
-	buf = read_file("events/header_page", &size);
+	buf = read_top_file("events/header_page", &size);
 	if (!buf)
 		goto out_pevent;
 	ret = tep_parse_header_page(tep, buf, size, sizeof(unsigned long));
@@ -4596,7 +4689,7 @@ static void check_plugin(const char *plugin)
 	if (strcmp(plugin, "nop") == 0)
 		return;
 
-	buf = read_file("available_tracers", NULL);
+	buf = read_top_file("available_tracers", NULL);
 	if (!buf)
 		die("No plugins available");
 
-- 
2.24.1