cgroups: fix cgroup_event_listener error handling

The error handling in cgroup_event_listener.c did not correctly deal
with either an error opening either <control_file> or
cgroup.event_control.  Due to an uninitialized variable the program
exit code was undefined if either of these opens failed.

This patch simplifies and corrects cgroup_event_listener.c error
handling by:
1. using err*() rather than printf(),exit()
2. depending on process exit to close open files

With this patch failures always return non-zero error.

Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/tools/cgroup/cgroup_event_listener.c b/tools/cgroup/cgroup_event_listener.c
index 3e082f9..4eb5507 100644 (file)
--- a/tools/cgroup/cgroup_event_listener.c
+++ b/tools/cgroup/cgroup_event_listener.c
@@ -5,6 +5,7 @@
  */
 
 #include <assert.h>
+#include <err.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
@@ -15,7 +16,7 @@
 
 #include <sys/eventfd.h>
 
-#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>\n"
+#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
 
 int main(int argc, char **argv)
 {
@@ -26,49 +27,33 @@ int main(int argc, char **argv)
        char line[LINE_MAX];
        int ret;
 
-       if (argc != 3) {
-               fputs(USAGE_STR, stderr);
-               return 1;
-       }
+       if (argc != 3)
+               errx(1, "%s", USAGE_STR);
 
        cfd = open(argv[1], O_RDONLY);
-       if (cfd == -1) {
-               fprintf(stderr, "Cannot open %s: %s\n", argv[1],
-                               strerror(errno));
-               goto out;
-       }
+       if (cfd == -1)
+               err(1, "Cannot open %s", argv[1]);
 
        ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
                        dirname(argv[1]));
-       if (ret >= PATH_MAX) {
-               fputs("Path to cgroup.event_control is too long\n", stderr);
-               goto out;
-       }
+       if (ret >= PATH_MAX)
+               errx(1, "Path to cgroup.event_control is too long");
 
        event_control = open(event_control_path, O_WRONLY);
-       if (event_control == -1) {
-               fprintf(stderr, "Cannot open %s: %s\n", event_control_path,
-                               strerror(errno));
-               goto out;
-       }
+       if (event_control == -1)
+               err(1, "Cannot open %s", event_control_path);
 
        efd = eventfd(0, 0);
-       if (efd == -1) {
-               perror("eventfd() failed");
-               goto out;
-       }
+       if (efd == -1)
+               err(1, "eventfd() failed");
 
        ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
-       if (ret >= LINE_MAX) {
-               fputs("Arguments string is too long\n", stderr);
-               goto out;
-       }
+       if (ret >= LINE_MAX)
+               errx(1, "Arguments string is too long");
 
        ret = write(event_control, line, strlen(line) + 1);
-       if (ret == -1) {
-               perror("Cannot write to cgroup.event_control");
-               goto out;
-       }
+       if (ret == -1)
+               err(1, "Cannot write to cgroup.event_control");
 
        while (1) {
                uint64_t result;
@@ -77,34 +62,21 @@ int main(int argc, char **argv)
                if (ret == -1) {
                        if (errno == EINTR)
                                continue;
-                       perror("Cannot read from eventfd");
-                       break;
+                       err(1, "Cannot read from eventfd");
                }
                assert(ret == sizeof(result));
 
                ret = access(event_control_path, W_OK);
                if ((ret == -1) && (errno == ENOENT)) {
-                               puts("The cgroup seems to have removed.");
-                               ret = 0;
-                               break;
-               }
-
-               if (ret == -1) {
-                       perror("cgroup.event_control "
-                                       "is not accessible any more");
+                       puts("The cgroup seems to have removed.");
                        break;
                }
 
+               if (ret == -1)
+                       err(1, "cgroup.event_control is not accessible any more");
+
                printf("%s %s: crossed\n", argv[1], argv[2]);
        }
 
-out:
-       if (efd >= 0)
-               close(efd);
-       if (event_control >= 0)
-               close(event_control);
-       if (cfd >= 0)
-               close(cfd);
-
-       return (ret != 0);
+       return 0;
 }