text: /****************************************************************************
   * fs/vfs/fs_lseek.c
   *
   *   Copyright (C) 2008, 2017 Gregory Nutt. All rights reserved.
   *   Author: Gregory Nutt <gnutt@nuttx.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <sys/types.h>
  #include <unistd.h>
  #include <sched.h>
  #include <errno.h>
  #include <assert.h>
  
  #include "inode/inode.h"
  
  #if CONFIG_NFILE_DESCRIPTORS > 0
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: file_seek
   *
   * Description:
   *   This is the internal implementation of lseek.  See the comments in
   *   lseek() for further information.
   *
   * Input Parameters:
   *   file     File structure instance
   *   offset   Defines the offset to position to
   *   whence   Defines how to use offset
   *
   * Returned Value:
   *   The resulting offset on success.  A negated errno value is returned on
   *   any failure (see lseek comments).
   *
   ****************************************************************************/
  
  off_t file_seek(FAR struct file *filep, off_t offset, int whence)
  {
    FAR struct inode *inode;
    int ret;
  
    DEBUGASSERT(filep);
    inode =  filep->f_inode;
  
    /* Invoke the file seek method if available */
  
    if (inode && inode->u.i_ops && inode->u.i_ops->seek)
      {
        ret = (int)inode->u.i_ops->seek(filep, offset, whence);
        if (ret < 0)
          {
            return ret;
          }
      }
    else
      {
        /* No... Just set the common file position value */
  
        switch (whence)
          {
            case SEEK_CUR:
              offset += filep->f_pos;
  
              /* FALLTHROUGH */
  
            case SEEK_SET:
              if (offset >= 0)
                {
                  filep->f_pos = offset; /* Might be beyond the end-of-file */
                  break;
                }
              else
                {
                  return -EINVAL;
                }
              break;
  
            case SEEK_END:
              return -ENOSYS;
  
            default:
              return -EINVAL;
          }
      }
  
    return filep->f_pos;
  }
  
  /****************************************************************************
   * Name: lseek
   *
   * Description:
   *   The lseek() function repositions the offset of the open file associated
   *   with the file descriptor fd to the argument 'offset' according to the
   *   directive 'whence' as follows:
   *
   *   SEEK_SET
   *      The offset is set to offset bytes.
   *   SEEK_CUR
   *      The offset is set to its current location plus offset bytes.
   *   SEEK_END
   *      The offset is set to the size of the file plus offset bytes.
   *
   *  The lseek() function allows the file offset to be set beyond the end of the
   *  file (but this does not change the size of the file). If data is later written
   *  at this point, subsequent reads of the data in the gap (a "hole") return null
   *  bytes ('\0') until data is actually written into the gap.
   *
   * Input Parameters:
   *   fd       File descriptor of device
   *   offset   Defines the offset to position to
   *   whence   Defines how to use offset
   *
   * Returned Value:
   *   The resulting offset on success.  -1 on failure withi errno set properly:
   *
   *   EBADF      fd is not an open file descriptor.
   *   EINVAL     whence  is  not one of SEEK_SET, SEEK_CUR, SEEK_END; or the
   *              resulting file offset would be negative, or beyond the end of a
   *              seekable device.
   *   EOVERFLOW  The resulting file offset cannot be represented in an off_t.
   *   ESPIPE     fd is associated with a pipe, socket, or FIFO.
   *
   ****************************************************************************/
  
  off_t lseek(int fd, off_t offset, int whence)
  {
    FAR struct file *filep;
    off_t newpos;
    int errcode;
    int ret;
  
    /* Get the file structure corresponding to the file descriptor. */
  
    ret = fs_getfilep(fd, &filep);
    if (ret < 0)
      {
        errcode = -ret;
        goto errout;
      }
  
    DEBUGASSERT(filep != NULL);
  
    /* Then let file_seek do the real work */
  
    newpos = file_seek(filep, offset, whence);
    if (newpos < 0)
      {
        errcode = (int)-newpos;
        goto errout;
      }
  
     return newpos;
  
  errout:
    set_errno(errcode);
    return (off_t)ERROR;
  }
  
  #endif
  