[PATCH perf/core v7 07/21] perf symbol: Cleanup the code flow of dso__find_kallsyms

[Masami Hiramatsu]

Cleanup the code flow of dso__find_kallsyms() to remove
redundant checking code and add some comment for readability.

Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
 tools/perf/util/symbol.c |   60 +++++++++++++++++++++-------------------------
 1 file changed, 27 insertions(+), 33 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index e112bbd..b2b06b7 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1629,6 +1629,15 @@ static int find_matching_kcore(struct map *map, char 
*dir, size_t dir_sz)
        return ret;
 }
 
+static bool filename__readable(const char *file)
+{
+       int fd = open(file, O_RDONLY);
+       if (fd < 0)
+               return false;
+       close(fd);
+       return true;
+}
+
 static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 {
        u8 host_build_id[BUILD_ID_SIZE];
@@ -1648,45 +1657,33 @@ static char *dso__find_kallsyms(struct dso *dso, struct 
map *map)
                                 sizeof(host_build_id)) == 0)
                is_host = dso__build_id_equal(dso, host_build_id);
 
-       build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
-
-       scnprintf(path, sizeof(path), "%s/%s/%s", buildid_dir,
-                 DSO__NAME_KCORE, sbuild_id);
-
-       /* Use /proc/kallsyms if possible */
+       /* Try a fast path for /proc/kallsyms if possible */
        if (is_host) {
-               DIR *d;
-               int fd;
-
-               /* If no cached kcore go with /proc/kallsyms */
-               d = opendir(path);
-               if (!d)
-                       goto proc_kallsyms;
-               closedir(d);
-
                /*
-                * Do not check the build-id cache, until we know we cannot use
-                * /proc/kcore.
+                * Do not check the build-id cache, unless we know we cannot use
+                * /proc/kcore or module maps don't match to /proc/kallsyms.
                 */
-               fd = open("/proc/kcore", O_RDONLY);
-               if (fd != -1) {
-                       close(fd);
-                       /* If module maps match go with /proc/kallsyms */
-                       if (!validate_kcore_addresses("/proc/kallsyms", map))
-                               goto proc_kallsyms;
-               }
-
-               /* Find kallsyms in build-id cache with kcore */
-               if (!find_matching_kcore(map, path, sizeof(path)))
-                       return strdup(path);
-
-               goto proc_kallsyms;
+               if (filename__readable("/proc/kcore") &&
+                   !validate_kcore_addresses("/proc/kallsyms", map))
+                       goto proc_kallsyms;
        }
 
+       build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+
        /* Find kallsyms in build-id cache with kcore */
+       scnprintf(path, sizeof(path), "%s/%s/%s",
+                 buildid_dir, DSO__NAME_KCORE, sbuild_id);
+
        if (!find_matching_kcore(map, path, sizeof(path)))
                return strdup(path);
 
+       /* Use current /proc/kallsyms if possible */
+       if (is_host) {
+proc_kallsyms:
+               return strdup("/proc/kallsyms");
+       }
+
+       /* Finally, find a cache of kallsyms */
        scnprintf(path, sizeof(path), "%s/%s/%s",
                  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
 
@@ -1697,9 +1694,6 @@ static char *dso__find_kallsyms(struct dso *dso, struct 
map *map)
        }
 
        return strdup(path);
-
-proc_kallsyms:
-       return strdup("/proc/kallsyms");
 }
 
 static int dso__load_kernel_sym(struct dso *dso, struct map *map,