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- /****************************************************************************
- * fs/vfs/fs_pwrite.c
- *
- * Copyright (C) 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 <unistd.h>
- #include <errno.h>
- #include <nuttx/cancelpt.h>
- #include <nuttx/fs/fs.h>
- /****************************************************************************
- * Public Functions
- ****************************************************************************/
- /****************************************************************************
- * Name: file_pwrite
- *
- * Description:
- * Equivalent to the standard pwrite function except that is accepts a
- * struct file instance instead of a file descriptor. Currently used
- * only by aio_write();
- *
- ****************************************************************************/
- ssize_t file_pwrite(FAR struct file *filep, FAR const void *buf,
- size_t nbytes, off_t offset)
- {
- off_t savepos;
- off_t pos;
- ssize_t ret;
- /* Perform the seek to the current position. This will not move the
- * file pointer, but will return its current setting
- */
- savepos = file_seek(filep, 0, SEEK_CUR);
- if (savepos < 0)
- {
- /* file_seek might fail if this if the media is not seekable */
- return (ssize_t)savepos;
- }
- /* Then seek to the correct position in the file */
- pos = file_seek(filep, offset, SEEK_SET);
- if (pos < 0)
- {
- /* This might fail is the offset is beyond the end of file */
- return (ssize_t)pos;
- }
- /* Then perform the write operation */
- ret = file_write(filep, buf, nbytes);
- /* Restore the file position */
- pos = file_seek(filep, savepos, SEEK_SET);
- if (pos < 0 && ret >= 0)
- {
- /* This really should not fail */
- ret = (ssize_t)pos;
- }
- return ret;
- }
- /****************************************************************************
- * Name: pwrite
- *
- * Description:
- * The pwrite() function performs the same action as write(), except that
- * it writes into a given position without changing the file pointer. The
- * first three arguments to pwrite() are the same as write() with the
- * addition of a fourth argument offset for the desired position inside
- * the file.
- *
- * NOTE: This function could have been wholly implemented within libc but
- * it is not. Why? Because if pwrite were implemented in libc, it would
- * require four system calls. If it is implemented within the kernel,
- * only three.
- *
- * Input Parameters:
- * fd file descriptor (or socket descriptor) to write to
- * buf Data to write
- * nbytes Length of data to write
- *
- * 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.
- * See write() return values
- *
- * Assumptions/Limitations:
- * POSIX requires that opening a file with the O_APPEND flag should have no
- * effect on the location at which pwrite() writes data. However, on NuttX
- * like on Linux, if a file is opened with O_APPEND, pwrite() appends data
- * to the end of the file, regardless of the value of offset.
- *
- ****************************************************************************/
- ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset)
- {
- FAR struct file *filep;
- ssize_t ret;
- /* pread() is a cancellation point */
- enter_cancellation_point();
- /* Get the file structure corresponding to the file descriptor. */
- ret = (ssize_t)fs_getfilep(fd, &filep);
- if (ret < 0)
- {
- goto errout;
- }
- /* Let file_pwrite do the real work */
- ret = file_pwrite(filep, buf, nbytes, offset);
- if (ret < 0)
- {
- goto errout;
- }
- leave_cancellation_point();
- return ret;
- errout:
- set_errno((int)-ret);
- leave_cancellation_point();
- return (ssize_t)ERROR;
- }
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