[PATCH 1/2] perf/tools: add read/write buildid dir locks

[Milos Vyletel <milos@redhat.com>]

Protect access to buildid dir by flock to prevent race conditions. This
patch adds buildid_dir_read/write_lock/unlock functions.

Signed-off-by: Milos Vyletel <milos@redhat.com>
---
 tools/perf/util/build-id.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/build-id.h |  5 +++++
 2 files changed, 61 insertions(+)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 61867df..46c41e1 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -536,3 +536,59 @@ bool perf_session__read_build_ids(struct perf_session *session, bool with_hits)
 
 	return ret;
 }
+
+static int buildid_dir_lock(int op)
+{
+	int lockfd, wait = 30;
+	const size_t size = PATH_MAX;
+	char *lockfile = zalloc(size);
+
+	scnprintf(lockfile, size, "%s/.lock", buildid_dir);
+
+	lockfd = open(lockfile, O_RDONLY|O_CREAT, S_IRUSR);
+	if (lockfd  == -1)
+		goto out;
+
+	while (1) {
+		if (flock(lockfd, op | LOCK_NB) == 0)
+			goto out;
+		else if (wait == 0) {
+			close(lockfd);
+			lockfd = -1;
+			goto out;
+		}
+		if (--wait % 10 == 0)
+			pr_info("Waiting for %s lock to be available\n", buildid_dir);
+		usleep(100);
+	}
+
+out:
+	free(lockfile);
+	return lockfd;
+}
+
+static void buildid_dir_unlock(int fd)
+{
+	flock(fd, LOCK_UN);
+	close(fd);
+}
+
+void buildid_dir_write_lock(int *fd)
+{
+	*fd = buildid_dir_lock(LOCK_EX);
+}
+
+void buildid_dir_read_lock(int *fd)
+{
+	*fd = buildid_dir_lock(LOCK_SH);
+}
+
+void buildid_dir_write_unlock(int fd)
+{
+	buildid_dir_unlock(fd);
+}
+
+void buildid_dir_read_unlock(int fd)
+{
+	buildid_dir_unlock(fd);
+}
diff --git a/tools/perf/util/build-id.h b/tools/perf/util/build-id.h
index 8501122..326cd2e 100644
--- a/tools/perf/util/build-id.h
+++ b/tools/perf/util/build-id.h
@@ -31,4 +31,9 @@ int build_id_cache__add_s(const char *sbuild_id,
 int build_id_cache__remove_s(const char *sbuild_id);
 void disable_buildid_cache(void);
 
+void buildid_dir_write_lock(int *);
+void buildid_dir_read_lock(int *);
+void buildid_dir_write_unlock(int);
+void buildid_dir_read_unlock(int);
+
 #endif
-- 
2.4.0