dosfs: Remove fat_file_datasync()

The fat_file_datasync() read every cluster of the file into the cache
and then synchronized it step-by-step.  For unmodified buffers this is a
non-operation.  For modified buffers this will wake-up the swapout task
which performs then a single buffer write operation.  This is usually
quite inefficient.  Firstly we do single buffer writes, secondly we
may perform a lot of unnecessary read operations (for huge files this is
really bad), and thirdly this leads likely to cache evictions.

The synchronization procedure is replaced by a simple
rtems_bdbuf_sync_dev().  This has the side-effect that also buffers not
related to the file are synchronized, but since the modified list is
normally short this should be acceptable.

1 files changed, 31 insertions, 0 deletions

diff --git a/cpukit/libfs/src/dosfs/msdos_misc.c b/cpukit/libfs/src/dosfs/msdos_misc.c
index d11bd83f52..511ac44dda 100644
--- a/cpukit/libfs/src/dosfs/msdos_misc.c
+++ b/cpukit/libfs/src/dosfs/msdos_misc.c
@@ -1646,3 +1646,34 @@ int msdos_find_node_by_cluster_num_in_fat_file(
     }
     return MSDOS_NAME_NOT_FOUND_ERR;
 }
+
+int
+msdos_sync_unprotected(msdos_fs_info_t *fs_info)
+{
+    int rc = fat_buf_release(&fs_info->fat);
+    rtems_status_code sc = rtems_bdbuf_syncdev(fs_info->fat.vol.dd);
+    if (sc != RTEMS_SUCCESSFUL) {
+	errno = EIO;
+	rc = -1;
+    }
+
+    return rc;
+}
+
+int
+msdos_sync(rtems_libio_t *iop)
+{
+    int                rc = RC_OK;
+    rtems_status_code  sc = RTEMS_SUCCESSFUL;
+    msdos_fs_info_t   *fs_info = iop->pathinfo.mt_entry->fs_info;
+
+    sc = rtems_semaphore_obtain(fs_info->vol_sema, RTEMS_WAIT,
+                                MSDOS_VOLUME_SEMAPHORE_TIMEOUT);
+    if (sc != RTEMS_SUCCESSFUL)
+        rtems_set_errno_and_return_minus_one(EIO);
+
+    rc = msdos_sync_unprotected(fs_info);
+
+    rtems_semaphore_release(fs_info->vol_sema);
+    return rc;
+}