1 | /* Write data into multiple buffers. Base implementation for pwritev |
2 | and pwritev64. |
3 | Copyright (C) 2017-2022 Free Software Foundation, Inc. |
4 | This file is part of the GNU C Library. |
5 | |
6 | The GNU C Library is free software; you can redistribute it and/or |
7 | modify it under the terms of the GNU Lesser General Public |
8 | License as published by the Free Software Foundation; either |
9 | version 2.1 of the License, or (at your option) any later version. |
10 | |
11 | The GNU C Library is distributed in the hope that it will be useful, |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
14 | Lesser General Public License for more details. |
15 | |
16 | You should have received a copy of the GNU Lesser General Public |
17 | License along with the GNU C Library; if not, see |
18 | <https://www.gnu.org/licenses/>. */ |
19 | |
20 | #include <unistd.h> |
21 | #include <sys/uio.h> |
22 | #include <sys/param.h> |
23 | #include <errno.h> |
24 | #include <malloc.h> |
25 | |
26 | #include <ldsodefs.h> |
27 | #include <libc-pointer-arith.h> |
28 | |
29 | /* Write data pointed by the buffers described by IOVEC, which is a |
30 | vector of COUNT 'struct iovec's, to file descriptor FD at the given |
31 | position OFFSET without change the file pointer. The data is |
32 | written in the order specified. Operates just like 'write' (see |
33 | <unistd.h>) except that the data are taken from IOVEC instead of a |
34 | contiguous buffer. */ |
35 | ssize_t |
36 | PWRITEV (int fd, const struct iovec *vector, int count, OFF_T offset) |
37 | { |
38 | /* Find the total number of bytes to be read. */ |
39 | size_t bytes = 0; |
40 | for (int i = 0; i < count; ++i) |
41 | { |
42 | /* Check for ssize_t overflow. */ |
43 | if (SSIZE_MAX - bytes < vector[i].iov_len) |
44 | { |
45 | __set_errno (EINVAL); |
46 | return -1; |
47 | } |
48 | bytes += vector[i].iov_len; |
49 | } |
50 | |
51 | /* Allocate a temporary buffer to hold the data. It could be done with a |
52 | stack allocation, but due limitations on some system (Linux with |
53 | O_DIRECT) it aligns the buffer to pagesize. A possible optimization |
54 | would be querying if the syscall would impose any alignment constraint, |
55 | but 1. it is system specific (not meant in generic implementation), and |
56 | 2. it would make the implementation more complex, and 3. it will require |
57 | another syscall (fcntl). */ |
58 | void *buffer = __mmap (NULL, bytes, PROT_READ | PROT_WRITE, |
59 | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); |
60 | if (__glibc_unlikely (buffer == MAP_FAILED)) |
61 | return -1; |
62 | |
63 | /* Copy the data from BUFFER into the memory specified by VECTOR. */ |
64 | char *ptr = buffer; |
65 | for (int i = 0; i < count; ++i) |
66 | ptr = __mempcpy ((void *) ptr, (void *) vector[i].iov_base, |
67 | vector[i].iov_len); |
68 | |
69 | ssize_t ret = PWRITE (fd, buffer, bytes, offset); |
70 | |
71 | __munmap (buffer, bytes); |
72 | |
73 | return ret; |
74 | } |
75 | |