+static void grab_lockfile(void);
+static void release_lockfile(void);
+
+static const char *lockfile = EXP_LOCKFILE;
+static int _lockfd = -1;
+
+/*
+ * If we aren't careful, changes made by exportfs can be lost
+ * when multiple exports process run at once:
+ *
+ * exportfs process 1 exportfs process 2
+ * ------------------------------------------
+ * reads etab version A reads etab version A
+ * adds new export B adds new export C
+ * writes A+B writes A+C
+ *
+ * The locking in support/export/xtab.c will prevent mountd from
+ * seeing a partially written version of etab, and will prevent
+ * the two writers above from writing simultaneously and
+ * corrupting etab, but to prevent problems like the above we
+ * need these additional lockfile() routines.
+ */
+static void
+grab_lockfile()
+{
+ _lockfd = open(lockfile, O_CREAT|O_RDWR, 0666);
+ if (_lockfd != -1)
+ lockf(_lockfd, F_LOCK, 0);
+}
+static void
+release_lockfile()
+{
+ if (_lockfd != -1)
+ lockf(_lockfd, F_ULOCK, 0);
+}