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>

1 files changed, 44 insertions, 28 deletions

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index d5efa5092ce6..023dd3548a94 100644
--- 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;
 }