liblog: cache getuid() syscall

BUG: 15315766
Change-Id: I8f889a1c6ede74f2621f1b8ea5fda666c4b9cba2

1 files changed, 10 insertions, 7 deletions

diff --git a/liblog/logd_write.c b/liblog/logd_write.c
index 121d84d..f10eb8e 100644
--- a/liblog/logd_write.c
+++ b/liblog/logd_write.c
@@ -159,10 +159,14 @@ static int __write_to_log_kernel(log_id_t log_id, struct iovec *vec, size_t nr)
     struct timespec ts;
     log_time realtime_ts;
     size_t i, payload_size;
+    static uid_t last_uid = AID_ROOT; /* logd *always* starts up as AID_ROOT */
 
-    if (getuid() == AID_LOGD) {
+    if (last_uid == AID_ROOT) { /* have we called to get the UID yet? */
+        last_uid = getuid();
+    }
+    if (last_uid == AID_LOGD) { /* logd, after initialization and priv drop */
         /*
-         * ignore log messages we send to ourself.
+         * ignore log messages we send to ourself (logd).
          * Such log messages are often generated by libraries we depend on
          * which use standard Android logging.
          */
@@ -193,6 +197,10 @@ static int __write_to_log_kernel(log_id_t log_id, struct iovec *vec, size_t nr)
      *  };
      */
 
+    clock_gettime(CLOCK_REALTIME, &ts);
+    realtime_ts.tv_sec = ts.tv_sec;
+    realtime_ts.tv_nsec = ts.tv_nsec;
+
     log_id_buf = log_id;
     tid = gettid();
 
@@ -200,11 +208,6 @@ static int __write_to_log_kernel(log_id_t log_id, struct iovec *vec, size_t nr)
     newVec[0].iov_len    = sizeof_log_id_t;
     newVec[1].iov_base   = (unsigned char *) &tid;
     newVec[1].iov_len    = sizeof(tid);
-
-    clock_gettime(CLOCK_REALTIME, &ts);
-    realtime_ts.tv_sec = ts.tv_sec;
-    realtime_ts.tv_nsec = ts.tv_nsec;
-
     newVec[2].iov_base   = (unsigned char *) &realtime_ts;
     newVec[2].iov_len    = sizeof(log_time);