perf tools: Refactor comm/tgid lookup

Rather than parsing /proc/pid/status file one line at a time, read it
into a buffer in one shot and search for all strings in one pass.

tgid conversion also simplified -- removing the isspace walk. As noted
by Arnaldo those are not needed for atoi == strtol calls.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Joe Mario <jmario@redhat.com>
Link: http://lkml.kernel.org/r/1427747758-18510-1-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index d5efa5092ce6a578b5edc2824adc4c4d799c5699..023dd3548a942c635f6533bbfc2f8529c807d854 100644 (file)
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -49,48 +49,64 @@ static struct perf_sample synth_sample = {
        .period    = 1,
 };
 
+/*
+ * Assumes that the first 4095 bytes of /proc/pid/stat contains
+ * the comm and tgid.
+ */
 static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
 {
        char filename[PATH_MAX];
-       char bf[BUFSIZ];
-       FILE *fp;
-       size_t size = 0;
+       char bf[4096];
+       int fd;
+       size_t size = 0, n;
        pid_t tgid = -1;
+       char *nl, *name, *tgids;
 
        snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
 
-       fp = fopen(filename, "r");
-       if (fp == NULL) {
+       fd = open(filename, O_RDONLY);
+       if (fd < 0) {
                pr_debug("couldn't open %s\n", filename);
                return 0;
        }
 
-       while (!comm[0] || (tgid < 0)) {
-               if (fgets(bf, sizeof(bf), fp) == NULL) {
-                       pr_warning("couldn't get COMM and pgid, malformed %s\n",
-                                  filename);
-                       break;
-               }
+       n = read(fd, bf, sizeof(bf) - 1);
+       close(fd);
+       if (n <= 0) {
+               pr_warning("Couldn't get COMM and tgid for pid %d\n",
+                          pid);
+               return -1;
+       }
+       bf[n] = '\0';
 
-               if (memcmp(bf, "Name:", 5) == 0) {
-                       char *name = bf + 5;
-                       while (*name && isspace(*name))
-                               ++name;
-                       size = strlen(name) - 1;
-                       if (size >= len)
-                               size = len - 1;
-                       memcpy(comm, name, size);
-                       comm[size] = '\0';
-
-               } else if (memcmp(bf, "Tgid:", 5) == 0) {
-                       char *tgids = bf + 5;
-                       while (*tgids && isspace(*tgids))
-                               ++tgids;
-                       tgid = atoi(tgids);
-               }
+       name = strstr(bf, "Name:");
+       tgids = strstr(bf, "Tgid:");
+
+       if (name) {
+               name += 5;  /* strlen("Name:") */
+
+               while (*name && isspace(*name))
+                       ++name;
+
+               nl = strchr(name, '\n');
+               if (nl)
+                       *nl = '\0';
+
+               size = strlen(name);
+               if (size >= len)
+                       size = len - 1;
+               memcpy(comm, name, size);
+               comm[size] = '\0';
+       } else {
+               pr_debug("Name: string not found for pid %d\n", pid);
        }
 
-       fclose(fp);
+       if (tgids) {
+               tgids += 5;  /* strlen("Tgid:") */
+               tgid = atoi(tgids);
+       } else {
+               pr_debug("Tgid: string not found for pid %d\n", pid);
+       }
 
        return tgid;
 }