mappedfile: only release the buffer if fd changed (github #5)

lib/mappedfile.c

@@ -90,7 +90,6 @@ struct mappedfile {
     size_t map_size;
 
     /* the file itself */
-    ino_t map_ino;
     int fd;
 
     /* tracking */
@@ -226,6 +225,7 @@ EXPORTED int mappedfile_readlock(struct mappedfile *mf)
             return -EIO;
         }
         if (sbuf.st_ino == sbuffile.st_ino) break;
+        buf_free(&mf->map_buf);
 
         newfd = open(mf->fname, O_RDWR, 0644);
         if (newfd == -1) {
@@ -240,11 +240,6 @@ EXPORTED int mappedfile_readlock(struct mappedfile *mf)
 
     mf->lock_status = MF_READLOCKED;
 
-    /* XXX - can we guarantee the fd isn't reused? */
-    if (mf->map_ino != sbuf.st_ino) {
-        buf_free(&mf->map_buf);
-    }
-
     _ensure_mapped(mf, sbuf.st_size, /*update*/0);
 
     return 0;
@@ -255,23 +250,21 @@ EXPORTED int mappedfile_writelock(struct mappedfile *mf)
     int r;
     struct stat sbuf;
     const char *lockfailaction;
+    int changed = 0;
 
     assert(mf->lock_status == MF_UNLOCKED);
     assert(mf->fd != -1);
     assert(mf->is_rw);
     assert(!mf->dirty);
 
-    r = lock_reopen(mf->fd, mf->fname, &sbuf, &lockfailaction);
+    r = lock_reopen_ex(mf->fd, mf->fname, &sbuf, &lockfailaction, &changed);
     if (r < 0) {
         syslog(LOG_ERR, "IOERROR: %s %s: %m", lockfailaction, mf->fname);
         return r;
     }
     mf->lock_status = MF_WRITELOCKED;
 
-    /* XXX - can we guarantee the fd isn't reused? */
-    if (mf->map_ino != sbuf.st_ino) {
-        buf_free(&mf->map_buf);
-    }
+    if (changed) buf_free(&mf->map_buf);
 
     _ensure_mapped(mf, sbuf.st_size, /*update*/0);