workaround low mtime resolution by reloading isasl db few times

If isasl.pw is changed several times during one second (which is
resolution of mtime in struct stat), then we'll have stale password
database.

To prevent that we keep reloading isasl password for 2 mtime check
cycles. If mtime is still same, we can be sure that we haven't missed
updates.

Change-Id: Ia299aba6296b86ec0e569cf1d13bc9fbede0303a

1 files changed, 16 insertions, 3 deletions

diff --git a/daemon/isasl.c b/daemon/isasl.c
index 5ca1a39..bbc66d4 100644
--- a/daemon/isasl.c
+++ b/daemon/isasl.c
@@ -15,7 +15,10 @@
 #include "isasl.h"
 #include "memcached.h"
 
+#define MTIME_STABILITY_THRESHOLD 2
+
 static struct stat prev_stat = { 0 };
+static int mtime_stability_counter;
 
 static pthread_mutex_t uhash_lock = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t sasl_db_thread_lock = PTHREAD_MUTEX_INITIALIZER;
@@ -190,7 +193,7 @@ void sasl_dispose(sasl_conn_t **pconn)
 
 static bool isasl_is_fresh(void)
 {
-    bool rv = false;
+    bool rv = true;
     struct stat st;
     const char *filename = get_isasl_filename();
 
@@ -198,7 +201,17 @@ static bool isasl_is_fresh(void)
         if (stat(get_isasl_filename(), &st) < 0) {
             perror(get_isasl_filename());
         } else {
-            rv = prev_stat.st_mtime == st.st_mtime;
+            rv = (prev_stat.st_mtime != st.st_mtime);
+            if (rv) {
+                /* if mtime changes, reset stability counter */
+                mtime_stability_counter = MTIME_STABILITY_THRESHOLD;
+            } else if (mtime_stability_counter) {
+                /* if mtime haven't changed, but counter hasn't
+                 * reached zero, reply true (fresh data) and
+                 * decrement counter */
+                mtime_stability_counter--;
+                rv = true;
+            }
             prev_stat = st;
         }
     }
@@ -219,7 +232,7 @@ static void* check_isasl_db_thread(void* arg)
     while (run) {
         sleep(sleep_time);
 
-        if (!isasl_is_fresh()) {
+        if (isasl_is_fresh()) {
             load_user_db();
         }