143 lines
4.8 KiB
C
143 lines
4.8 KiB
C
/****************************************************************************
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* libs/libc/uio/lib_writev.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <sys/types.h>
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#include <sys/uio.h>
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#include <unistd.h>
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#include <errno.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: writev()
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*
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* Description:
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* The writev() function is equivalent to write(), except as described
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* below. The writev() function will gather output data from the 'iovcnt'
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* buffers specified by the members of the 'iov' array:
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* iov[0], iov[1], ..., iov[iovcnt-1].
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* The 'iovcnt' argument is valid if greater than 0 and less than or equal
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* to IOV_MAX, as defined in limits.h.
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*
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* Each iovec entry specifies the base address and length of an area in
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* memory from which data should be written. The writev() function always
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* writes a complete area before proceeding to the next.
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*
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* If 'filedes' refers to a regular file and all of the iov_len members in
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* the array pointed to by iov are 0, writev() will return 0 and have no
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* other effect. For other file types, the behavior is unspecified.
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*
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* TODO: If the sum of the iov_len values is greater than SSIZE_MAX, the
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* operation will fail and no data will be transferred.
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*
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* Input Parameters:
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* filedes - The open file descriptor for the file to be write
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* iov - Array of write buffer descriptors
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* iovcnt - Number of elements in iov[]
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*
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* Returned Value:
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* Upon successful completion, writev() shall return the number of bytes
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* actually written. Otherwise, it shall return a value of -1, the file-
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* pointer shall remain unchanged, and errno shall be set to indicate an
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* error. See write for the list of returned errno values. In addition,
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* the writev() function will fail if:
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*
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* EINVAL.
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* The sum of the iov_len values in the iov array overflowed an ssize_t
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* or The 'iovcnt' argument was less than or equal to 0, or greater than
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* IOV_MAX (Not implemented).
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*
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****************************************************************************/
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ssize_t writev(int fildes, FAR const struct iovec *iov, int iovcnt)
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{
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ssize_t ntotal;
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ssize_t nwritten;
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size_t remaining;
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FAR uint8_t *buffer;
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off_t pos;
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int i;
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/* Get the current file position in case we have to reset it */
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pos = lseek(fildes, 0, SEEK_CUR);
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/* Process each entry in the struct iovec array */
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for (i = 0, ntotal = 0; i < iovcnt; i++)
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{
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/* Ignore zero-length writes */
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if (iov[i].iov_len > 0)
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{
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buffer = iov[i].iov_base;
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remaining = iov[i].iov_len;
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/* Write repeatedly as necessary to write the entire buffer */
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do
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{
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/* NOTE: write() is a cancellation point */
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nwritten = write(fildes, buffer, remaining);
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/* Check for a write error */
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if (nwritten < 0)
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{
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if (pos != (off_t)-1)
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{
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/* Save the errno value */
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int save = get_errno();
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/* Restore the file position */
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lseek(fildes, pos, SEEK_SET);
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/* Restore the errno value */
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set_errno(save);
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}
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return ERROR;
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}
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/* Update pointers and counts in order to handle partial
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* buffer writes.
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*/
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buffer += nwritten;
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remaining -= nwritten;
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ntotal += nwritten;
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}
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while (remaining > 0);
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}
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}
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return ntotal;
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}
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