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>

1 files changed, 22 insertions, 50 deletions

diff --git a/tools/cgroup/cgroup_event_listener.c b/tools/cgroup/cgroup_event_listener.c
index 3e082f96dc12..4eb5507205c9 100644
--- 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;
 }