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108 lines
3.0 KiB
C
108 lines
3.0 KiB
C
/* Copyright (C) 2009-2016 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <limits.h>
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#include <stdbool.h>
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#include <sys/param.h>
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#if __WORDSIZE == 64 && !defined PREADV
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/* Hide the preadv64 declaration. */
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# define preadv64 __redirect_preadv64
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#endif
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#include <sys/uio.h>
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#include <bits/wordsize.h>
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#ifndef PREADV
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# define PREADV preadv
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# define PREAD __pread
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# define OFF_T off_t
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#endif
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static void
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ifree (char **ptrp)
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{
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free (*ptrp);
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}
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/* Read data from file descriptor FD at the given position OFFSET
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without change the file pointer, and put the result in the buffers
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described by VECTOR, which is a vector of COUNT 'struct iovec's.
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The buffers are filled in the order specified. Operates just like
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'pread' (see <unistd.h>) except that data are put in VECTOR instead
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of a contiguous buffer. */
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ssize_t
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PREADV (int fd, const struct iovec *vector, int count, OFF_T offset)
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{
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/* Find the total number of bytes to be read. */
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size_t bytes = 0;
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for (int i = 0; i < count; ++i)
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{
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/* Check for ssize_t overflow. */
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if (SSIZE_MAX - bytes < vector[i].iov_len)
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{
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__set_errno (EINVAL);
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return -1;
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}
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bytes += vector[i].iov_len;
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}
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/* Allocate a temporary buffer to hold the data. We should normally
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use alloca since it's faster and does not require synchronization
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with other threads. But we cannot if the amount of memory
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required is too large. */
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char *buffer;
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char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL;
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if (__libc_use_alloca (bytes))
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buffer = (char *) __alloca (bytes);
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else
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{
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malloced_buffer = buffer = (char *) malloc (bytes);
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if (buffer == NULL)
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return -1;
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}
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/* Read the data. */
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ssize_t bytes_read = PREAD (fd, buffer, bytes, offset);
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if (bytes_read < 0)
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return -1;
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/* Copy the data from BUFFER into the memory specified by VECTOR. */
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bytes = bytes_read;
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for (int i = 0; i < count; ++i)
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{
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size_t copy = MIN (vector[i].iov_len, bytes);
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(void) memcpy ((void *) vector[i].iov_base, (void *) buffer, copy);
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buffer += copy;
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bytes -= copy;
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if (bytes == 0)
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break;
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}
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return bytes_read;
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}
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#if __WORDSIZE == 64 && defined preadv64
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# undef preadv64
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strong_alias (preadv, preadv64)
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#endif
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