/****************************************************************************
 * libc/stdio/lib_readv.c
 *
 *   Copyright (C) 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 <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: readv()
 *
 * Description:
 *   The readv() function is equivalent to read(), except as described below.
 *   The readv() function places the input data into the iovcnt buffers
 *   specified by the members of the iov array: iov[0], iov[1], ...,
 *   iov[iovcnt-1].  The iovcnt argument is valid if greater than 0 and less
 *   than or equal to IOV_MAX as defined in limits.h.
 *
 *   Each iovec entry specifies the base address and length of an area in
 *   memory where data should be placed.  The readv() function will always
 *   fill an area completely before proceeding to the next.
 *
 *   Upon successful completion, readv() will mark for update the st_atime
 *   field of the file.
 *
 * Input Parameters:
 *   filedes - The open file descriptor for the file to be read
 *   iov     - Array of read buffer descriptors
 *   iovcnt  - Number of elements in iov[]
 *
 * Returned Value:
 *   Upon successful completion, readv() will return a non-negative integer
 *   indicating the number of bytes actually read.  Otherwise, the functions
 *   will return -1 and set errno to indicate the error.  See read().
 *
 ****************************************************************************/

ssize_t readv(int fildes, FAR const struct iovec *iov, int iovcnt)
{
  ssize_t ntotal;
  ssize_t nread;
  size_t remaining;
  FAR uint8_t *buffer;
  int i;

  /* Process each entry in the struct iovec array */

  for (i = 0, ntotal = 0; i < iovcnt; i++)
    {
      /* Ignore zero-length reads */

      if (iov[i].iov_len > 0)
        {
          buffer    = iov[i].iov_base;
          remaining = iov[i].iov_len;

          /* Read repeatedly as necessary to fill buffer */

          do
            {
              /* NOTE:  read() is a cancellation point */

              nread = read(fildes, buffer, remaining);

              /* Check for a read error */

              if (nread < 0)
                {
                  return nread;
                }

              /* Check for an end-of-file condition */

              else if (nread == 0)
                {
                  return ntotal;
                }

              /* Update pointers and counts in order to handle partial
               * buffer reads.
               */

              buffer    += nread;
              remaining -= nread;
              ntotal    += nread;
            }
          while (remaining > 0);
        }
    }

  return ntotal;
}