100 lines
2.9 KiB
C
100 lines
2.9 KiB
C
/****************************************************************************
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* libs/libc/uio/lib_preadv.c
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*
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* SPDX-License-Identifier: Apache-2.0
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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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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: preadv()
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*
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* Description:
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* The preadv() function is equivalent to pread(), except it takes
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* an iov array.
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*
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****************************************************************************/
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ssize_t preadv(int fildes, FAR const struct iovec *iov, int iovcnt,
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off_t offset)
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{
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ssize_t ntotal;
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ssize_t nread;
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size_t remaining;
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FAR uint8_t *buffer;
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int i;
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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 reads */
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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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/* Read repeatedly as necessary to fill buffer */
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do
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{
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/* NOTE: pread() is a cancellation point */
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nread = pread(fildes, buffer, remaining, offset + ntotal);
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/* Check for a read error */
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if (nread < 0)
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{
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return nread;
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}
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/* Check for an end-of-file condition */
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else if (nread == 0)
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{
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return ntotal;
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}
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/* Update pointers and counts in order to handle partial
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* buffer reads.
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*/
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buffer += nread;
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remaining -= nread;
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ntotal += nread;
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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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