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, 125 insertions, 162 deletions

diff --git a/cpukit/libcsupport/src/privateenv.c b/cpukit/libcsupport/src/privateenv.c
index 89137200b7..28f866272b 100644
--- a/cpukit/libcsupport/src/privateenv.c
+++ b/cpukit/libcsupport/src/privateenv.c
@@ -1,3 +1,9 @@
+/**
+ * @file
+ *
+ * @ingroup LibIOEnv
+ */
+
 /*
  *  Instantiate a private user environment for the calling thread.
  *
@@ -14,191 +20,148 @@
  */
 
 #if HAVE_CONFIG_H
-#include "config.h"
+  #include "config.h"
 #endif
 
-#include <stdlib.h> /* free */
+#define __RTEMS_VIOLATE_KERNEL_VISIBILITY__
+
+#include <stdlib.h>
 
-#include <rtems.h>
-#include <rtems/chain.h>
 #include <rtems/libio_.h>
+#include <rtems/score/thread.h>
 
-/* cleanup a user environment
- * NOTE: this must be called with
- *       thread dispatching disabled!
- */
-static void
-free_user_env(void *venv)
+static void free_user_env(void *arg)
 {
-  rtems_user_env_t *env = (rtems_user_env_t*) venv ;
-
-  if (env != &rtems_global_user_env
-  #ifdef HAVE_USERENV_REFCNT
-      && --env->refcnt <= 0
-  #endif
-  ) {
-    rtems_filesystem_freenode( &env->current_directory);
-    rtems_filesystem_freenode( &env->root_directory);
-    free(env);
+  rtems_user_env_t *env = arg;
+  bool uses_global_env = env == &rtems_global_user_env;
+
+  if (!uses_global_env) {
+    if (env->reference_count == 1) {
+      rtems_filesystem_global_location_release(env->current_directory);
+      rtems_filesystem_global_location_release(env->root_directory);
+      free(env);
+    } else {
+      --env->reference_count;
+    }
   }
 }
 
+static void free_user_env_protected(rtems_user_env_t *env)
+{
+  _Thread_Disable_dispatch();
+  free_user_env(env);
+  _Thread_Enable_dispatch();
+}
+
 rtems_status_code rtems_libio_set_private_env(void)
 {
   rtems_status_code sc = RTEMS_SUCCESSFUL;
-  rtems_id task_id = rtems_task_self();
-  rtems_filesystem_location_info_t root_loc;
-  rtems_filesystem_location_info_t current_loc;
-  rtems_user_env_t *new_env = NULL;
-  int rv = 0;
-
-  rv = rtems_filesystem_evaluate_path("/", 1, 0, &root_loc, 0);
-  if (rv != 0)
-    goto error_0;
-
-  rv = rtems_filesystem_evaluate_path("/", 1, 0, &current_loc, 0);
-  if (rv != 0)
-    goto error_1;
-
-  /* 
-   * Malloc is necessary whenever the current task does not
-   * have its own environment in place. This could be:
-   * a) it never had one
-   * OR
-   * b) it shared another task's environment
-   */
-
-  /* 
-   * Bharath: I'm not sure if the check can be reduced to
-   * if( rtems_current_user_env->task_id != task_id ) {
-   */
-
-  if (
-    rtems_current_user_env == &rtems_global_user_env
-      || rtems_current_user_env->task_id != task_id
-  ) {
-    new_env = malloc(sizeof(rtems_user_env_t));
-    if (new_env == NULL)
-      goto error_2;
-
-    #ifdef HAVE_USERENV_REFCNT
-      new_env->refcnt = 1;
-    #endif
-
-    sc = rtems_task_variable_add(
-      RTEMS_SELF,
-      (void*)&rtems_current_user_env,
-      (void(*)(void *))free_user_env
-    );
-    if (sc != RTEMS_SUCCESSFUL)
-      goto error_3;
-
-    rtems_current_user_env = new_env;
+  rtems_id self_task_id = rtems_task_self();
+  rtems_user_env_t *old_env = rtems_current_user_env;
+  bool uses_global_env = old_env == &rtems_global_user_env;
+  bool uses_shared_env = old_env->task_id != self_task_id;
+
+  if (uses_global_env || uses_shared_env) {
+    rtems_user_env_t *new_env = calloc(1, sizeof(*new_env));
+
+    if (new_env != NULL) {
+      *new_env = *old_env;
+      new_env->reference_count = 1;
+      new_env->task_id = self_task_id;
+      new_env->root_directory =
+        rtems_filesystem_global_location_obtain(&old_env->root_directory);
+      new_env->current_directory =
+        rtems_filesystem_global_location_obtain(&old_env->current_directory);
+
+      if (
+        !rtems_filesystem_global_location_is_null(new_env->root_directory)
+          && !rtems_filesystem_global_location_is_null(new_env->current_directory)
+      ) {
+        sc = rtems_task_variable_add(
+          RTEMS_SELF,
+          (void **) &rtems_current_user_env,
+          free_user_env
+        );
+        if (sc == RTEMS_SUCCESSFUL) {
+          free_user_env_protected(old_env);
+          rtems_current_user_env = new_env;
+        } else {
+          sc = RTEMS_TOO_MANY;
+        }
+      } else {
+        sc = RTEMS_UNSATISFIED;
+      }
+
+      if (sc != RTEMS_SUCCESSFUL) {
+        free_user_env(new_env);
+      }
+    } else {
+      sc = RTEMS_NO_MEMORY;
+    }
   }
 
-  /* Inherit the global values */
-  *rtems_current_user_env = rtems_global_user_env;
-
-  rtems_current_user_env->task_id = task_id;
-
-  /*
-   * Clone the pathlocs. In contrast to most other code we must _not_ free the
-   * original locs because what we are trying to do here is forking off clones.
-   * The reason is a pathloc can be allocated by the file system and needs to
-   * be freed when deleting the environment.
-   */
-  rtems_filesystem_root = root_loc;
-  rtems_filesystem_current = current_loc;
-
-  return RTEMS_SUCCESSFUL;
-
-error_3:
-  free(new_env);
-
-error_2:
-  rtems_filesystem_freenode(&current_loc);
-
-error_1:
-  rtems_filesystem_freenode(&root_loc);
-
-error_0:
-  return RTEMS_NO_MEMORY;
+  return sc;
 }
 
-/*
- *  Share the same private environment between two tasks:
- *      Task_id (remote) and RTEMS_SELF(current).
- */
-
-/* NOTE:
- *
- * THIS CODE HAS NO PROTECTION IMPLEMENTED
- *
- * Tasks who wish to share their environments must
- *
- *  a) assert that no participants are concurrently
- *     executing
- *     libio_share_private_env() and/or libio_set_private_env()
- *
- *  b) mutex access to rtems_filesystem_current, rtems_filesytem_root
- *     while changing any of those (chdir(), chroot()).
- */
-
 rtems_status_code rtems_libio_share_private_env(rtems_id task_id)
 {
-  rtems_status_code  sc;
-  rtems_user_env_t * shared_user_env;
-  rtems_id           current_task_id;
-
-  /* 
-   * get current task id 
-   */
-  current_task_id = rtems_task_self();
-
-  /*
-   * If this was an attempt to share the task with self,
-   * if somebody wanted to do it... Lets tell them, its shared
-   */
-
-  if( task_id == current_task_id )
-    return RTEMS_SUCCESSFUL;
-  /* 
-   * Try to get the requested user environment 
-   */
-  sc = rtems_task_variable_get(
-	 task_id,
-	 (void*)&rtems_current_user_env, 
-	 (void*)&shared_user_env );
-
-  /* 
-   * If it was not successful, return the error code 
-   */
-    if (sc != RTEMS_SUCCESSFUL)
-      return sc;
-
-    /* 
-     * If we are here, we have the required environment to be
-     * shared with the current task
-    */
+  rtems_status_code sc = RTEMS_SUCCESSFUL;
+  rtems_id self_task_id = rtems_task_self();
+
+  if (task_id != RTEMS_SELF && self_task_id != task_id) {
+    rtems_user_env_t *env;
 
     /*
-     * If we have a current environment in place, we need to 
-     * free it, since we will be sharing the variable with the
-     * shared_user_env
+     * We have to disable the thread dispatching to prevent deletion of the
+     * environment in the meantime.
      */
-
-  if (rtems_current_user_env->task_id==current_task_id) {
-    rtems_user_env_t  *tmp = rtems_current_user_env;
-    free_user_env( tmp );
+    _Thread_Disable_dispatch();
+    sc = rtems_task_variable_get(
+      task_id,
+      (void *) &rtems_current_user_env, 
+      (void *) &env
+    );
+    if (sc == RTEMS_SUCCESSFUL) {
+      ++env->reference_count;
+    } else {
+      sc = RTEMS_UNSATISFIED;
+    }
+    _Thread_Enable_dispatch();
+
+    if (sc == RTEMS_SUCCESSFUL) {
+      sc = rtems_task_variable_add(
+        RTEMS_SELF,
+        (void **) &rtems_current_user_env,
+        free_user_env
+      );
+      if (sc == RTEMS_SUCCESSFUL) {
+        free_user_env_protected(rtems_current_user_env);
+        rtems_current_user_env = env;
+      } else {
+        free_user_env_protected(env);
+        sc = RTEMS_TOO_MANY;
+      }
+    }
   }
 
-  /* the current_user_env is the same pointer that remote env */
-  rtems_current_user_env = shared_user_env;
+  return sc;
+}
 
-  /* increase the reference count */
-#ifdef HAVE_USERENV_REFCNT
-  rtems_current_user_env->refcnt++;
-#endif
+void rtems_libio_use_global_env(void)
+{
+  rtems_status_code sc = RTEMS_SUCCESSFUL;
+  rtems_user_env_t *env = rtems_current_user_env;
+  bool uses_private_env = env != &rtems_global_user_env;
 
-  return RTEMS_SUCCESSFUL;
+  if (uses_private_env) {
+    sc = rtems_task_variable_delete(
+      RTEMS_SELF,
+      (void **) &rtems_current_user_env
+    );
+    if (sc != RTEMS_SUCCESSFUL) {
+      rtems_fatal_error_occurred(0xdeadbeef);
+    }
+
+    rtems_current_user_env = &rtems_global_user_env;
+  }
 }