text: /****************************************************************************
   * fs/dirent/fs_opendir.c
   *
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.  The
   * ASF licenses this file to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance with the
   * License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
   * License for the specific language governing permissions and limitations
   * under the License.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <stdbool.h>
  #include <string.h>
  #include <dirent.h>
  #include <assert.h>
  #include <errno.h>
  
  #include <nuttx/kmalloc.h>
  #include <nuttx/fs/fs.h>
  #include <nuttx/fs/dirent.h>
  
  #include "inode/inode.h"
  
  /****************************************************************************
   * Private Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: open_mountpoint
   *
   * Description:
   *   Handle the case where the inode to be opened is within a mountpoint.
   *
   * Input Parameters:
   *   inode -- the inode of the mountpoint to open
   *   relpath -- the relative path within the mountpoint to open
   *   dir -- the dirent structure to be initialized
   *
   * Returned Value:
   *   On success, OK is returned; Otherwise, a positive errno is returned.
   *
   ****************************************************************************/
  
  #ifndef CONFIG_DISABLE_MOUNTPOINT
  static inline int open_mountpoint(FAR struct inode *inode,
                                    FAR const char *relpath,
                                    FAR struct fs_dirent_s *dir)
  {
    int ret;
  
    /* The inode itself as the 'root' of mounted volume.  The actually
     * directory is at relpath into the* mounted filesystem.
     *
     * Verify that the mountpoint inode  supports the opendir() method
     */
  
    if (!inode->u.i_mops || !inode->u.i_mops->opendir)
      {
        return -ENOSYS;
      }
  
    /* Take reference to the mountpoint inode.  Note that we do not use
     * inode_addref() because we already hold the tree semaphore.
     */
  
    inode->i_crefs++;
  
    /* Perform the opendir() operation */
  
    ret = inode->u.i_mops->opendir(inode, relpath, dir);
    if (ret < 0)
      {
        /* We now need to back off our reference to the inode.  We can't
         * call inode_release() to do that unless we release the tree
         * semaphore.  The following should be safe because:  (1) after the
         * reference count was incremented above it should be >=1 so it should
         * not decrement below zero, and (2) we hold the tree semaphore so no
         * other thread should be able to change the reference count.
         */
  
        inode->i_crefs--;
        DEBUGASSERT(inode->i_crefs >= 0);
  
        /* Negate the error value so that it can be used to set errno */
  
        return ret;
      }
  
    return OK;
  }
  #endif
  
  /****************************************************************************
   * Name: open_pseudodir
   *
   * Description:
   *   Handle the case where the inode to be opened is within the top-level
   *   pseudo-file system.
   *
   * Input Parameters:
   *   inode -- the inode of the mountpoint to open
   *   dir -- the dirent structure to be initialized
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  static void open_pseudodir(FAR struct inode *inode,
                             FAR struct fs_dirent_s *dir)
  {
    /* We have a valid pseudo-filesystem node.  Take two references on the
     * inode -- one for the parent (fd_root) and one for the child (fd_next).
     * Note that we do not call inode_addref because we are holding the tree
     * semaphore and that would result in deadlock.
     */
  
    inode->i_crefs       += 2;
    dir->fd_root          = inode; /* Save the inode where we start */
    dir->u.pseudo.fd_next = inode; /* This is the next node to use for readdir() */
  
    /* Flag the inode as belonging to the pseudo-filesystem */
  
  #ifndef CONFIG_DISABLE_MOUNTPOINT
    DIRENT_SETPSEUDONODE(dir->fd_flags);
  #endif
  }
  
  /****************************************************************************
   * Name: open_emptydir
   *
   * Description:
   *   Handle the case where the inode to be opened is an empty, directory node
   *   within the top-level pseudo-file system.  That is, it has no operations
   *   and, therefore, it must be a directory node.  But is has no children
   *   to be enumerated either.
   *
   * Input Parameters:
   *   dir -- the dirent structure to be initialized
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  static inline void open_emptydir(FAR struct fs_dirent_s *dir)
  {
    /* We have a valid, but empty pseudo-filesystem node.  fd_next is NULL
     * meaning that we are already at the end of the list of its children.
     * fd_root is NULL so that if the directory is rewound, it will still be
     * at the end of the list.
     */
  
  #if 0 /* Already nullified by kumm_zalloc */
    dir->fd_root          = NULL; /* Save the inode where we start */
    dir->u.pseudo.fd_next = NULL; /* We are at the end of the list */
  #endif
  
    /* Flag the inode as belonging to the pseudo-filesystem */
  
  #ifndef CONFIG_DISABLE_MOUNTPOINT
    DIRENT_SETPSEUDONODE(dir->fd_flags);
  #endif
  }
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: opendir
   *
   * Description:
   *   The  opendir() function opens a directory stream corresponding to the
   *   directory name, and returns a pointer to the directory stream. The
   *   stream is positioned at the first entry in the directory.
   *
   * Input Parameters:
   *   path -- the directory to open
   *
   * Returned Value:
   *   The opendir() function returns a pointer to the directory stream.  On
   *   error, NULL is returned, and errno is set appropriately.
   *
   *   EACCES  - Permission denied.
   *   EMFILE  - Too many file descriptors in use by process.
   *   ENFILE  - Too many files are currently open in the
   *             system.
   *   ENOENT  - Directory does not exist, or name is an empty
   *             string.
   *   ENOMEM  - Insufficient memory to complete the operation.
   *   ENOTDIR - 'path' is not a directory.
   *
   ****************************************************************************/
  
  FAR DIR *opendir(FAR const char *path)
  {
    FAR struct inode *inode = NULL;
    FAR struct fs_dirent_s *dir;
    struct inode_search_s desc;
  #ifndef CONFIG_DISABLE_MOUNTPOINT
    FAR const char *relpath = NULL;
  #endif
    int ret;
  
    /* If we are given 'nothing' then we will interpret this as
     * request for the root inode.
     */
  
    SETUP_SEARCH(&desc, path, false);
  
    ret = inode_semtake();
    if (ret < 0)
      {
        goto errout;
      }
  
    /* Find the node matching the path. */
  
    ret = inode_search(&desc);
    if (ret >= 0)
      {
        inode   = desc.node;
        DEBUGASSERT(inode != NULL);
  #ifndef CONFIG_DISABLE_MOUNTPOINT
        relpath = desc.relpath;
  #endif
      }
  
    /* Did we get an inode? */
  
    if (inode == NULL)
      {
        /* Inode for 'path' does not exist. */
  
        ret = -ENOTDIR;
        goto errout_with_semaphore;
      }
  
    /* Allocate a type DIR -- which is little more than an inode
     * container.
     */
  
    dir = (FAR struct fs_dirent_s *)kumm_zalloc(sizeof(struct fs_dirent_s));
    if (!dir)
      {
        /* Insufficient memory to complete the operation. */
  
        ret = -ENOMEM;
        goto errout_with_semaphore;
      }
  
    /* Populate the DIR structure and return it to the caller.  The way that
     * we do this depends on whenever this is a "normal" pseudo-file-system
     * inode or a file system mountpoint.
     */
  
    dir->fd_position = 0;      /* This is the position in the read stream */
  
    /* Is this a node in the pseudo filesystem? Or a mountpoint? */
  
  #ifndef CONFIG_DISABLE_MOUNTPOINT
    if (INODE_IS_MOUNTPT(inode))
      {
        /* Yes, the node is a file system mountpoint */
  
        dir->fd_root = inode;  /* Save the inode where we start */
  
        /* Open the directory at the relative path */
  
        ret = open_mountpoint(inode, relpath, dir);
        if (ret != OK)
          {
            goto errout_with_direntry;
          }
      }
    else
  #endif
      {
        /* The node is part of the root pseudo file system.  Does the inode
         * have a child? If so that the child would be the 'root' of a list
         * of nodes under the directory.
         */
  
        FAR struct inode *child = inode->i_child;
        if (child != NULL)
          {
            /* It looks we have a valid pseudo-filesystem directory node. */
  
            open_pseudodir(child, dir);
          }
        else if (!inode->u.i_ops)
          {
            /* This is a dangling node with no children and no operations. Set
             * up to enumerate an empty directory.
             */
  
            open_emptydir(dir);
          }
        else
          {
            ret = -ENOTDIR;
            goto errout_with_direntry;
          }
      }
  
    RELEASE_SEARCH(&desc);
    inode_semgive();
    return ((FAR DIR *)dir);
  
    /* Nasty goto's make error handling simpler */
  
  errout_with_direntry:
    kumm_free(dir);
  
  errout_with_semaphore:
    RELEASE_SEARCH(&desc);
    inode_semgive();
  
  errout:
    set_errno(-ret);
    return NULL;
  }
  