libmount: introduce reference counting for libmnt_lock

[thirdparty/util-linux.git] / libmount / src / lock.c

diff --git a/libmount/src/lock.c b/libmount/src/lock.c
index cbc74a6034cc265b8142ebb5848bcd92da377d3d..8aca8a7768d3af6a36517f4e3754d87441034fe4 100644 (file)
--- a/libmount/src/lock.c
+++ b/libmount/src/lock.c
@@ -36,6 +36,7 @@
  * lock handler
  */
 struct libmnt_lock {
+       int     refcount;       /* reference counter */
        char    *lockfile;      /* path to lock file (e.g. /etc/mtab~) */
        int     lockfile_fd;    /* lock file descriptor */
 
@@ -73,6 +74,7 @@ struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id __attribute__((_
        if (!ml)
                goto err;
 
+       ml->refcount = 1;
        ml->lockfile_fd = -1;
        ml->lockfile = lo;
 
@@ -89,17 +91,56 @@ err:
  * mnt_free_lock:
  * @ml: struct libmnt_lock handler
  *
- * Deallocates mnt_lock.
+ * Deallocates libmnt_lock. This function does not care about reference count. Don't
+ * use this function directly -- it's better to use mnt_unref_lock().
+ *
+ * The reference counting is supported since util-linux v2.40.
  */
 void mnt_free_lock(struct libmnt_lock *ml)
 {
        if (!ml)
                return;
-       DBG(LOCKS, ul_debugobj(ml, "free%s", ml->locked ? " !!! LOCKED !!!" : ""));
+
+       DBG(LOCKS, ul_debugobj(ml, "free%s [refcount=%d]",
+                                       ml->locked ? " !!! LOCKED !!!" : "",
+                                       ml->refcount));
        free(ml->lockfile);
        free(ml);
 }
 
+/**
+ * mnt_ref_lock:
+ * @ml: lock pointer
+ *
+ * Increments reference counter.
+ *
+ * Since: 2.40
+ */
+void mnt_ref_lock(struct libmnt_lock *ml)
+{
+       if (ml) {
+               ml->refcount++;
+               /*DBG(FS, ul_debugobj(fs, "ref=%d", ml->refcount));*/
+       }
+}
+
+/**
+ * mnt_unref_lock:
+ * @ml: lock pointer
+ *
+ * De-increments reference counter, on zero the @ml is automatically
+ * deallocated by mnt_free_lock).
+ */
+void mnt_unref_lock(struct libmnt_lock *ml)
+{
+       if (ml) {
+               ml->refcount--;
+               /*DBG(FS, ul_debugobj(fs, "unref=%d", ml->refcount));*/
+               if (ml->refcount <= 0)
+                       mnt_free_lock(ml);
+       }
+}
+
 /**
  * mnt_lock_block_signals:
  * @ml: struct libmnt_lock handler
@@ -286,7 +327,7 @@ static void clean_lock(void)
        if (!lock)
                return;
        mnt_unlock_file(lock);
-       mnt_free_lock(lock);
+       mnt_unref_lock(lock);
 }
 
 static void __attribute__((__noreturn__)) sig_handler(int sig)
@@ -367,7 +408,7 @@ static int test_lock(struct libmnt_test *ts __attribute__((unused)),
                increment_data(datafile, verbose, l);
 
                mnt_unlock_file(lock);
-               mnt_free_lock(lock);
+               mnt_unref_lock(lock);
                lock = NULL;
 
                /* The mount command usually finishes after a mtab update. We