lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame^] | 1 | /* Copyright (C) 2009-2015 Free Software Foundation, Inc. |
| 2 | This file is part of the GNU C Library. |
| 3 | |
| 4 | The GNU C Library is free software; you can redistribute it and/or |
| 5 | modify it under the terms of the GNU Lesser General Public |
| 6 | License as published by the Free Software Foundation; either |
| 7 | version 2.1 of the License, or (at your option) any later version. |
| 8 | |
| 9 | The GNU C Library is distributed in the hope that it will be useful, |
| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 12 | Lesser General Public License for more details. |
| 13 | |
| 14 | You should have received a copy of the GNU Lesser General Public |
| 15 | License along with the GNU C Library; if not, see |
| 16 | <http://www.gnu.org/licenses/>. */ |
| 17 | |
| 18 | #include <errno.h> |
| 19 | #include <stdlib.h> |
| 20 | #include <unistd.h> |
| 21 | #include <string.h> |
| 22 | #include <limits.h> |
| 23 | #include <stdbool.h> |
| 24 | #include <sys/param.h> |
| 25 | #if __WORDSIZE == 64 && !defined PREADV |
| 26 | /* Hide the preadv64 declaration. */ |
| 27 | # define preadv64 __redirect_preadv64 |
| 28 | #endif |
| 29 | #include <sys/uio.h> |
| 30 | #include <bits/wordsize.h> |
| 31 | |
| 32 | #ifndef PREADV |
| 33 | # define PREADV preadv |
| 34 | # define PREAD __pread |
| 35 | # define OFF_T off_t |
| 36 | #endif |
| 37 | |
| 38 | |
| 39 | static void |
| 40 | ifree (char **ptrp) |
| 41 | { |
| 42 | free (*ptrp); |
| 43 | } |
| 44 | |
| 45 | |
| 46 | /* Read data from file descriptor FD at the given position OFFSET |
| 47 | without change the file pointer, and put the result in the buffers |
| 48 | described by VECTOR, which is a vector of COUNT 'struct iovec's. |
| 49 | The buffers are filled in the order specified. Operates just like |
| 50 | 'pread' (see <unistd.h>) except that data are put in VECTOR instead |
| 51 | of a contiguous buffer. */ |
| 52 | ssize_t |
| 53 | PREADV (int fd, const struct iovec *vector, int count, OFF_T offset) |
| 54 | { |
| 55 | /* Find the total number of bytes to be read. */ |
| 56 | size_t bytes = 0; |
| 57 | for (int i = 0; i < count; ++i) |
| 58 | { |
| 59 | /* Check for ssize_t overflow. */ |
| 60 | if (SSIZE_MAX - bytes < vector[i].iov_len) |
| 61 | { |
| 62 | __set_errno (EINVAL); |
| 63 | return -1; |
| 64 | } |
| 65 | bytes += vector[i].iov_len; |
| 66 | } |
| 67 | |
| 68 | /* Allocate a temporary buffer to hold the data. We should normally |
| 69 | use alloca since it's faster and does not require synchronization |
| 70 | with other threads. But we cannot if the amount of memory |
| 71 | required is too large. */ |
| 72 | char *buffer; |
| 73 | char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL; |
| 74 | if (__libc_use_alloca (bytes)) |
| 75 | buffer = (char *) __alloca (bytes); |
| 76 | else |
| 77 | { |
| 78 | malloced_buffer = buffer = (char *) malloc (bytes); |
| 79 | if (buffer == NULL) |
| 80 | return -1; |
| 81 | } |
| 82 | |
| 83 | /* Read the data. */ |
| 84 | ssize_t bytes_read = PREAD (fd, buffer, bytes, offset); |
| 85 | if (bytes_read < 0) |
| 86 | return -1; |
| 87 | |
| 88 | /* Copy the data from BUFFER into the memory specified by VECTOR. */ |
| 89 | bytes = bytes_read; |
| 90 | for (int i = 0; i < count; ++i) |
| 91 | { |
| 92 | size_t copy = MIN (vector[i].iov_len, bytes); |
| 93 | |
| 94 | (void) memcpy ((void *) vector[i].iov_base, (void *) buffer, copy); |
| 95 | |
| 96 | buffer += copy; |
| 97 | bytes -= copy; |
| 98 | if (bytes == 0) |
| 99 | break; |
| 100 | } |
| 101 | |
| 102 | return bytes_read; |
| 103 | } |
| 104 | #if __WORDSIZE == 64 && defined preadv64 |
| 105 | # undef preadv64 |
| 106 | strong_alias (preadv, preadv64) |
| 107 | #endif |