| /* Read data into multiple buffers. Base implementation for preadv |
| and preadv64. |
| Copyright (C) 2017-2018 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 |
| <http://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; |
| } |