[PATCH v1 02/25] perf pmu: Avoid a path name copy

[Ian Rogers <irogers@google.com>]

Rather than read a base path and append into a 2nd path, read the base
path directly into output buffer and append to that.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/pmu.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index a7f05e4dda97..7683c6749d66 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -1756,17 +1756,19 @@ int perf_pmu__event_source_devices_fd(void)
  * then pathname will be filled with
  * "/sys/bus/event_source/devices/cs_etm/format"
  *
- * Return 0 if the sysfs mountpoint couldn't be found or if no
- * characters were written.
+ * Return 0 if the sysfs mountpoint couldn't be found, if no characters were
+ * written or if the buffer size is exceeded.
  */
 int perf_pmu__pathname_scnprintf(char *buf, size_t size,
 				 const char *pmu_name, const char *filename)
 {
-	char base_path[PATH_MAX];
+	size_t len;
 
-	if (!perf_pmu__event_source_devices_scnprintf(base_path, sizeof(base_path)))
+	len = perf_pmu__event_source_devices_scnprintf(buf, size);
+	if (!len || (len + strlen(pmu_name) + strlen(filename) + 1)  >= size)
 		return 0;
-	return scnprintf(buf, size, "%s%s/%s", base_path, pmu_name, filename);
+
+	return scnprintf(buf + len, size - len, "%s/%s", pmu_name, filename);
 }
 
 int perf_pmu__pathname_fd(int dirfd, const char *pmu_name, const char *filename, int flags)
-- 
2.42.0.rc1.204.g551eb34607-goog