perf tools: Use readdir() instead of deprecated readdir_r()

Commit-ID:  7093b4c963cc4e344e490c774924a180602a7092
Gitweb:     http://git.kernel.org/tip/7093b4c963cc4e344e490c774924a180602a7092
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Fri, 8 Apr 2016 11:32:15 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Fri, 8 Apr 2016 11:32:15 -0300

perf tools: Use readdir() instead of deprecated readdir_r()

The readdir() function is thread safe as long as just one thread uses a DIR, which is the case when synthesizing events for pre-existing threads by traversing /proc, so, to avoid breaking the build with glibc-2.23.90 (upcoming 2.24), use it instead of readdir_r().

See: http://man7.org/linux/man-pages/man3/readdir.3.html

"However, in modern implementations (including the glibc implementation), concurrent calls to readdir() that specify different directory streams are thread-safe. In cases where multiple threads must read from the same directory stream, using readdir() with external synchronization is still preferable to the use of the deprecated readdir_r(3) function."

Noticed while building on a Fedora Rawhide docker container.

CC /tmp/build/perf/util/event.o
util/event.c: In function '__event__synthesize_thread':
util/event.c:466:2: error: 'readdir_r' is deprecated [-Werror=deprecated-declarations]

    while (!readdir_r(tasks, &dirent, &next) && next) {
    ^~~~~
  In file included from /usr/include/features.h:368:0,
                   from /usr/include/stdint.h:25,
                   from /usr/lib/gcc/x86_64-redhat-linux/6.0.0/include/stdint.h:9,
                   from /git/linux/tools/include/linux/types.h:6,
                   from util/event.c:1:

/usr/include/dirent.h:189:12: note: declared here

---
 tools/perf/util/event.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

index b689590..f6fcc68 100644
@@ -434,7 +434,7 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 {
 	char filename[PATH_MAX];
 	DIR *tasks;
-	struct dirent dirent, *next;
+	struct dirent *dirent;
 	pid_t tgid, ppid;
 	int rc = 0;
 

@@ -463,11 +463,11 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 		return 0;
 	}
 
-	while (!readdir_r(tasks, &dirent, &next) && next) {
+	while ((dirent = readdir(tasks)) != NULL) {
 		char *end;
 		pid_t _pid;
 
-		_pid = strtol(dirent.d_name, &end, 10);
+		_pid = strtol(dirent->d_name, &end, 10);
 		if (*end)
 			continue;
 

@@ -576,7 +576,7 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
 {
 	DIR *proc;
 	char proc_path[PATH_MAX];
-	struct dirent dirent, *next;
+	struct dirent *dirent;
 	union perf_event *comm_event, *mmap_event, *fork_event;
 	int err = -1;
 

@@ -601,9 +601,9 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
 	if (proc == NULL)
 		goto out_free_fork;
 
-	while (!readdir_r(proc, &dirent, &next) && next) {
+	while ((dirent = readdir(proc)) != NULL) {
 		char *end;
-		pid_t pid = strtol(dirent.d_name, &end, 10);
+		pid_t pid = strtol(dirent->d_name, &end, 10);
 
 		if (*end) /* only interested in proper numerical dirents */
 			continue;