Filesystem: Reference counting for locations

 o A new data structure rtems_filesystem_global_location_t was
   introduced to be used for
    o the mount point location in the mount table entry,
    o the file system root location in the mount table entry,
    o the root directory location in the user environment, and
    o the current directory location in the user environment.
   During the path evaluation global start locations are obtained to
   ensure that the current file system instance will be not unmounted in
   the meantime.
 o The user environment uses now reference counting and is protected
   from concurrent access.
 o The path evaluation process was completely rewritten and simplified.
   The IMFS, RFS, NFS, and DOSFS use now a generic path evaluation
   method.  Recursive calls in the path evaluation have been replaced
   with iteration to avoid stack overflows.  Only the evaluation of
   symbolic links is recursive.  No dynamic memory allocations and
   intermediate buffers are used in the high level path evaluation.  No
   global locks are held during the file system instance specific path
   evaluation process.
 o Recursive symbolic link evaluation is now limited by
   RTEMS_FILESYSTEM_SYMLOOP_MAX.  Applications can retrieve this value
   via sysconf().
 o The device file system (devFS) uses now no global variables and
   allocation from the workspace.  Node names are allocated from the
   heap.
 o The upper layer lseek() performs now some parameter checks.
 o The upper layer ftruncate() performs now some parameter checks.
 o unmask() is now restricted to the RWX flags and protected from
   concurrent access.
 o The fchmod_h and rmnod_h file system node handlers are now a file
   system operation.
 o The unlink_h operation has been removed.  All nodes are now destroyed
   with the rmnod_h operation.
 o New lock_h, unlock_h, clonenod_h, and are_nodes_equal_h file system
   operations.
 o The path evaluation and file system operations are now protected by
   per file system instance lock and unlock operations.
 o Fix and test file descriptor duplicate in fcntl().
 o New test fstests/fsnofs01.

1 files changed, 218 insertions, 0 deletions

diff --git a/cpukit/libcsupport/src/sup_fs_location.c b/cpukit/libcsupport/src/sup_fs_location.c
new file mode 100644
index 0000000000..5234c01ddc
--- /dev/null
+++ b/cpukit/libcsupport/src/sup_fs_location.c
@@ -0,0 +1,218 @@
+/*
+ * Copyright (c) 2012 embedded brains GmbH.  All rights reserved.
+ *
+ *  embedded brains GmbH
+ *  Obere Lagerstr. 30
+ *  82178 Puchheim
+ *  Germany
+ *  <rtems@embedded-brains.de>
+ *
+ * The license and distribution terms for this file may be
+ * found in the file LICENSE in this distribution or at
+ * http://www.rtems.com/license/LICENSE.
+ */
+
+#if HAVE_CONFIG_H
+  #include "config.h"
+#endif
+
+#define __RTEMS_VIOLATE_KERNEL_VISIBILITY__
+
+#include <stdlib.h>
+
+#include <rtems/libio_.h>
+#include <rtems/score/thread.h>
+
+static rtems_filesystem_global_location_t *deferred_released_global_locations;
+
+rtems_filesystem_location_info_t *rtems_filesystem_location_copy(
+  rtems_filesystem_location_info_t *dst,
+  const rtems_filesystem_location_info_t *src
+)
+{
+  dst->node_access = src->node_access;
+  dst->node_access_2 = src->node_access_2;
+  dst->handlers = src->handlers;
+  dst->ops = src->ops;
+  dst->mt_entry = src->mt_entry;
+  rtems_filesystem_location_add_to_mt_entry(dst);
+
+  return dst;
+}
+
+void rtems_filesystem_location_detach(
+  rtems_filesystem_location_info_t *detach
+)
+{
+  rtems_filesystem_location_free(detach);
+  rtems_filesystem_location_initialize_to_null(detach);
+}
+
+void rtems_filesystem_location_copy_and_detach(
+  rtems_filesystem_location_info_t *copy,
+  rtems_filesystem_location_info_t *detach
+)
+{
+  rtems_filesystem_location_copy(copy, detach);
+  rtems_filesystem_location_remove_from_mt_entry(detach);
+  rtems_filesystem_location_initialize_to_null(detach);
+}
+
+rtems_filesystem_global_location_t *rtems_filesystem_location_transform_to_global(
+  rtems_filesystem_location_info_t *loc
+)
+{
+  rtems_filesystem_global_location_t *global_loc = malloc(sizeof(*global_loc));
+
+  if (global_loc != NULL) {
+    global_loc->reference_count = 1;
+    global_loc->deferred_released_next = NULL;
+    global_loc->deferred_released_count = 0;
+    rtems_filesystem_location_copy(&global_loc->location, loc);
+    rtems_filesystem_location_remove_from_mt_entry(loc);
+  } else {
+    rtems_filesystem_location_free(loc);
+    global_loc = rtems_filesystem_global_location_obtain_null();
+    errno = ENOMEM;
+  }
+
+  return global_loc;
+}
+
+void rtems_filesystem_global_location_assign(
+  rtems_filesystem_global_location_t **lhs_global_loc_ptr,
+  rtems_filesystem_global_location_t *rhs_global_loc
+)
+{
+  rtems_filesystem_mt_entry_declare_lock_context(lock_context);
+  rtems_filesystem_global_location_t *lhs_global_loc;
+
+  rtems_filesystem_mt_entry_lock(lock_context);
+  lhs_global_loc = *lhs_global_loc_ptr;
+  *lhs_global_loc_ptr = rhs_global_loc;
+  rtems_filesystem_mt_entry_unlock(lock_context);
+
+  rtems_filesystem_global_location_release(lhs_global_loc);
+}
+
+static void release_with_count(
+  rtems_filesystem_global_location_t *global_loc,
+  int count
+)
+{
+  rtems_filesystem_mount_table_entry_t *mt_entry =
+    global_loc->location.mt_entry;
+  rtems_filesystem_mt_entry_declare_lock_context(lock_context);
+  bool do_free;
+  bool do_unmount;
+
+  rtems_filesystem_mt_entry_lock(lock_context);
+  global_loc->reference_count -= count;
+  do_free = global_loc->reference_count == 0;
+  do_unmount = rtems_filesystem_is_ready_for_unmount(mt_entry);
+  rtems_filesystem_mt_entry_unlock(lock_context);
+
+  if (do_free) {
+    rtems_filesystem_location_free(&global_loc->location);
+    free(global_loc);
+  }
+
+  if (do_unmount) {
+    rtems_filesystem_do_unmount(mt_entry);
+  }
+}
+
+static void deferred_release(void)
+{
+  rtems_filesystem_global_location_t *current = NULL;
+
+  do {
+    int count = 0;
+
+    _Thread_Disable_dispatch();
+    current = deferred_released_global_locations;
+    if (current != NULL) {
+      deferred_released_global_locations = current->deferred_released_next;
+      count = current->deferred_released_count;
+      current->deferred_released_next = NULL;
+      current->deferred_released_count = 0;
+    }
+    _Thread_Enable_dispatch();
+
+    if (current != NULL) {
+      release_with_count(current, count);
+    }
+  } while (current != NULL);
+}
+
+rtems_filesystem_global_location_t *rtems_filesystem_global_location_obtain(
+  rtems_filesystem_global_location_t *const *global_loc_ptr
+)
+{
+  rtems_filesystem_mt_entry_declare_lock_context(lock_context);
+  rtems_filesystem_global_location_t *global_loc;
+
+  if (deferred_released_global_locations != NULL) {
+    deferred_release();
+  }
+
+  rtems_filesystem_mt_entry_lock(lock_context);
+  global_loc = *global_loc_ptr;
+  if (global_loc == NULL || !global_loc->location.mt_entry->mounted) {
+    global_loc = &rtems_filesystem_global_location_null;
+    errno = ENXIO;
+  }
+  ++global_loc->reference_count;
+  rtems_filesystem_mt_entry_unlock(lock_context);
+
+  return global_loc;
+}
+
+void rtems_filesystem_global_location_release(
+  rtems_filesystem_global_location_t *global_loc
+)
+{
+  if (!_Thread_Dispatch_in_critical_section()) {
+    release_with_count(global_loc, 1);
+  } else {
+    if (global_loc->deferred_released_count == 0) {
+      rtems_filesystem_global_location_t *head =
+        deferred_released_global_locations;
+
+      global_loc->deferred_released_count = 1;
+      global_loc->deferred_released_next = head;
+      deferred_released_global_locations = global_loc;
+    } else {
+      ++global_loc->deferred_released_count;
+    }
+  }
+}
+
+void rtems_filesystem_location_remove_from_mt_entry(
+  rtems_filesystem_location_info_t *loc
+)
+{
+  rtems_filesystem_mt_entry_declare_lock_context(lock_context);
+  bool do_unmount;
+
+  rtems_filesystem_mt_entry_lock(lock_context);
+  rtems_chain_extract_unprotected(&loc->mt_entry_node);
+  do_unmount = rtems_filesystem_is_ready_for_unmount(loc->mt_entry);
+  rtems_filesystem_mt_entry_unlock(lock_context);
+
+  if (do_unmount) {
+    rtems_filesystem_do_unmount(loc->mt_entry);
+  }
+}
+
+void rtems_filesystem_do_unmount(
+  rtems_filesystem_mount_table_entry_t *mt_entry
+)
+{
+  rtems_filesystem_mt_lock();
+  rtems_chain_extract_unprotected(&mt_entry->mt_node);
+  rtems_filesystem_mt_unlock();
+  rtems_filesystem_global_location_release(mt_entry->mt_point_node);
+  (*mt_entry->mt_fs_root->location.ops->fsunmount_me_h)(mt_entry);
+  free(mt_entry);
+}