mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-22 21:10:07 +00:00
86 lines
2.9 KiB
C
86 lines
2.9 KiB
C
/* Read data into multiple buffers. Base implementation for preadv
|
|
and preadv64.
|
|
Copyright (C) 2017-2023 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#include <unistd.h>
|
|
#include <sys/uio.h>
|
|
#include <sys/param.h>
|
|
#include <errno.h>
|
|
#include <malloc.h>
|
|
|
|
#include <ldsodefs.h>
|
|
#include <libc-pointer-arith.h>
|
|
|
|
/* Read data from file descriptor FD at the given position OFFSET
|
|
without change the file pointer, and put the result in the buffers
|
|
described by VECTOR, which is a vector of COUNT 'struct iovec's.
|
|
The buffers are filled in the order specified. Operates just like
|
|
'pread' (see <unistd.h>) except that data are put in VECTOR instead
|
|
of a contiguous buffer. */
|
|
ssize_t
|
|
PREADV (int fd, const struct iovec *vector, int count, OFF_T offset)
|
|
{
|
|
/* Find the total number of bytes to be read. */
|
|
size_t bytes = 0;
|
|
for (int i = 0; i < count; ++i)
|
|
{
|
|
/* Check for ssize_t overflow. */
|
|
if (SSIZE_MAX - bytes < vector[i].iov_len)
|
|
{
|
|
__set_errno (EINVAL);
|
|
return -1;
|
|
}
|
|
bytes += vector[i].iov_len;
|
|
}
|
|
|
|
/* Allocate a temporary buffer to hold the data. It could be done with a
|
|
stack allocation, but due limitations on some system (Linux with
|
|
O_DIRECT) it aligns the buffer to pagesize. A possible optimization
|
|
would be querying if the syscall would impose any alignment constraint,
|
|
but 1. it is system specific (not meant in generic implementation), and
|
|
2. it would make the implementation more complex, and 3. it will require
|
|
another syscall (fcntl). */
|
|
void *buffer = __mmap (NULL, bytes, PROT_READ | PROT_WRITE,
|
|
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
|
|
if (__glibc_unlikely (buffer == MAP_FAILED))
|
|
return -1;
|
|
|
|
ssize_t bytes_read = PREAD (fd, buffer, bytes, offset);
|
|
if (bytes_read < 0)
|
|
goto end;
|
|
|
|
/* Copy the data from BUFFER into the memory specified by VECTOR. */
|
|
bytes = bytes_read;
|
|
void *buf = buffer;
|
|
for (int i = 0; i < count; ++i)
|
|
{
|
|
size_t copy = MIN (vector[i].iov_len, bytes);
|
|
|
|
memcpy (vector[i].iov_base, buf, copy);
|
|
|
|
buf += copy;
|
|
bytes -= copy;
|
|
if (bytes == 0)
|
|
break;
|
|
}
|
|
|
|
end:
|
|
__munmap (buffer, bytes);
|
|
return bytes_read;
|
|
}
|