tools api fs: Diet cgroupfs_find_mountpoint()

Reduce the number of buffers and hopefully make it more efficient. :)

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201216090556.813996-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/api/fs/cgroup.c b/tools/lib/api/fs/cgroup.c
index 813236d..262a422 100644 (file)
--- a/tools/lib/api/fs/cgroup.c
+++ b/tools/lib/api/fs/cgroup.c
@@ -11,9 +11,10 @@
 int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
 {
        FILE *fp;
-       char mountpoint[PATH_MAX + 1], tokens[PATH_MAX + 1], type[PATH_MAX + 1];
-       char path_v2[PATH_MAX + 1];
-       char *token, *saved_ptr = NULL;
+       char *line = NULL;
+       size_t len = 0;
+       char *p, *path;
+       char mountpoint[PATH_MAX];
 
        fp = fopen("/proc/mounts", "r");
        if (!fp)
@@ -25,38 +26,57 @@ int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
         * the given subsystem.  If we found v1, just use it.  If not we can
         * use v2 path as a fallback.
         */
-       path_v2[0] = '\0';
+       mountpoint[0] = '\0';
 
-       while (fscanf(fp, "%*s %"__stringify(PATH_MAX)"s %"__stringify(PATH_MAX)"s %"
-                               __stringify(PATH_MAX)"s %*d %*d\n",
-                               mountpoint, type, tokens) == 3) {
+       /*
+        * The /proc/mounts has the follow format:
+        *
+        *   <devname> <mount point> <fs type> <options> ...
+        *
+        */
+       while (getline(&line, &len, fp) != -1) {
+               /* skip devname */
+               p = strchr(line, ' ');
+               if (p == NULL)
+                       continue;
 
-               if (!strcmp(type, "cgroup")) {
+               /* save the mount point */
+               path = ++p;
+               p = strchr(p, ' ');
+               if (p == NULL)
+                       continue;
 
-                       token = strtok_r(tokens, ",", &saved_ptr);
+               *p++ = '\0';
 
-                       while (token != NULL) {
-                               if (subsys && !strcmp(token, subsys)) {
-                                       /* found */
-                                       fclose(fp);
+               /* check filesystem type */
+               if (strncmp(p, "cgroup", 6))
+                       continue;
 
-                                       if (strlen(mountpoint) < maxlen) {
-                                               strcpy(buf, mountpoint);
-                                               return 0;
-                                       }
-                                       return -1;
-                               }
-                               token = strtok_r(NULL, ",", &saved_ptr);
-                       }
+               if (p[6] == '2') {
+                       /* save cgroup v2 path */
+                       strcpy(mountpoint, path);
+                       continue;
                }
 
-               if (!strcmp(type, "cgroup2"))
-                       strcpy(path_v2, mountpoint);
+               /* now we have cgroup v1, check the options for subsystem */
+               p += 7;
+
+               p = strstr(p, subsys);
+               if (p == NULL)
+                       continue;
+
+               /* sanity check: it should be separated by a space or a comma */
+               if (!strchr(" ,", p[-1]) || !strchr(" ,", p[strlen(subsys)]))
+                       continue;
+
+               strcpy(mountpoint, path);
+               break;
        }
+       free(line);
        fclose(fp);
 
-       if (path_v2[0] && strlen(path_v2) < maxlen) {
-               strcpy(buf, path_v2);
+       if (mountpoint[0] && strlen(mountpoint) < maxlen) {
+               strcpy(buf, mountpoint);
                return 0;
        }
        return -1;