text: /****************************************************************************
   * fs/vfs/fs_read.c
   *
   *   Copyright (C) 2007-2009, 2012-2014, 2016-2017 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 <sys/socket.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <sched.h>
  #include <errno.h>
  
  #include <nuttx/cancelpt.h>
  #include <nuttx/net/net.h>
  
  #include "inode/inode.h"
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: file_read
   *
   * Description:
   *   file_read() is an interanl OS interface.  It is functionally similar to
   *   the standard read() interface except:
   *
   *    - It does not modify the errno variable,
   *    - It is not a cancellation point,
   *    - It does not handle socket descriptors, and
   *    - It accepts a file structure instance instead of file descriptor.
   *
   * Input Parameters:
   *   filep  - File structure instance
   *   buf    - User-provided to save the data
   *   nbytes - The maximum size of the user-provided buffer
   *
   * Returned Value:
   *   The positive non-zero number of bytes read on success, 0 on if an
   *   end-of-file condition, or a negated errno value on any failure.
   *
   ****************************************************************************/
  
  ssize_t file_read(FAR struct file *filep, FAR void *buf, size_t nbytes)
  {
    FAR struct inode *inode;
    int ret = -EBADF;
  
    DEBUGASSERT(filep);
    inode = filep->f_inode;
  
    /* Was this file opened for read access? */
  
    if ((filep->f_oflags & O_RDOK) == 0)
      {
        /* No.. File is not read-able */
  
        ret = -EACCES;
      }
  
    /* Is a driver or mountpoint registered? If so, does it support the read
     * method?
     */
  
    else if (inode != NULL && inode->u.i_ops && inode->u.i_ops->read)
      {
        /* Yes.. then let it perform the read.  NOTE that for the case of the
         * mountpoint, we depend on the read methods being identical in
         * signature and position in the operations vtable.
         */
  
        ret = (int)inode->u.i_ops->read(filep, (FAR char *)buf, (size_t)nbytes);
      }
  
    /* Return the number of bytes read (or possibly an error code) */
  
    return ret;
  }
  
  /****************************************************************************
   * Name: nx_read
   *
   * Description:
   *   nx_read() is an internal OS interface.  It is functionally similar to
   *   the standard read() interface except:
   *
   *    - It does not modify the errno variable, and
   *    - It is not a cancellation point.
   *
   * Input Parameters:
   *   fd     - File descriptor to read from
   *   buf    - User-provided to save the data
   *   nbytes - The maximum size of the user-provided buffer
   *
   * Returned Value:
   *   The positive non-zero number of bytes read on success, 0 on if an
   *   end-of-file condition, or a negated errno value on any failure.
   *
   ****************************************************************************/
  
  ssize_t nx_read(int fd, FAR void *buf, size_t nbytes)
  {
    /* Did we get a valid file descriptor? */
  
  #if CONFIG_NFILE_DESCRIPTORS > 0
    if ((unsigned int)fd >= CONFIG_NFILE_DESCRIPTORS)
  #endif
      {
  #if defined(CONFIG_NET) && CONFIG_NSOCKET_DESCRIPTORS > 0
        /* No.. If networking is enabled, read() is the same as recv() with
         * the flags parameter set to zero.
         */
  
        return nx_recv(fd, buf, nbytes, 0);
  #else
        /* No networking... it is a bad descriptor in any event */
  
        return -EBADF;
  #endif
      }
  
  #if CONFIG_NFILE_DESCRIPTORS > 0
    else
      {
        FAR struct file *filep;
        ssize_t ret;
  
        /* The descriptor is in a valid range to file descriptor... do the
         * read.  First, get the file structure.  Note that on failure,
         * fs_getfilep() will set the errno variable.
         */
  
        ret = (ssize_t)fs_getfilep(fd, &filep);
        if (ret < 0)
          {
            return ret;
          }
  
        /* Then let file_read do all of the work. */
  
        return file_read(filep, buf, nbytes);
      }
  #else
    /* I don't think we can get here */
  
    return -ENOSYS;
  #endif
  }
  
  /****************************************************************************
   * Name: read
   *
   * Description:
   *   The standard, POSIX read interface.
   *
   * Input Parameters:
   *   fd     - File descriptor to read from
   *   buf    - User-provided to save the data
   *   nbytes - The maximum size of the user-provided buffer
   *
   * Returned Value:
   *   The positive non-zero number of bytes read on success, 0 on if an
   *   end-of-file condition, or -1 on failure with errno set appropriately.
   *
   ****************************************************************************/
  
  ssize_t read(int fd, FAR void *buf, size_t nbytes)
  {
    ssize_t ret;
  
    /* read() is a cancellation point */
  
    (void)enter_cancellation_point();
  
    /* Let nx_read() do the real work */
  
    ret = nx_read(fd, buf, nbytes);
    if (ret < 0)
      {
        set_errno(-ret);
        ret = ERROR;
      }
  
    leave_cancellation_point();
    return ret;
  }
  