| 1 | /* Read block from given position in file without changing file pointer. |
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| 2 | POSIX version. |
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| 3 | Copyright (C) 1997-2022 Free Software Foundation, Inc. |
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| 4 | This file is part of the GNU C Library. |
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| 5 | |
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| 6 | The GNU C Library is free software; you can redistribute it and/or |
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| 7 | modify it under the terms of the GNU Lesser General Public |
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| 8 | License as published by the Free Software Foundation; either |
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| 9 | version 2.1 of the License, or (at your option) any later version. |
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| 10 | |
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| 11 | The GNU C Library is distributed in the hope that it will be useful, |
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| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 14 | Lesser General Public License for more details. |
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| 15 | |
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| 16 | You should have received a copy of the GNU Lesser General Public |
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| 17 | License along with the GNU C Library; if not, see |
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| 18 | <https://www.gnu.org/licenses/>. */ |
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| 19 | |
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| 20 | #include <errno.h> |
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| 21 | #include <unistd.h> |
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| 22 | |
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| 23 | /* Note: This implementation of pread is not multithread-safe. */ |
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| 24 | |
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| 25 | ssize_t |
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| 26 | __libc_pread (int fd, void *buf, size_t nbyte, off_t offset) |
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| 27 | { |
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| 28 | /* Since we must not change the file pointer preserve the value so that |
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| 29 | we can restore it later. */ |
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| 30 | int save_errno; |
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| 31 | ssize_t result; |
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| 32 | off_t old_offset = __libc_lseek (fd: fd, offset: 0, SEEK_CUR); |
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| 33 | if (old_offset == (off_t) -1) |
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| 34 | return -1; |
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| 35 | |
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| 36 | /* Set to wanted position. */ |
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| 37 | if (__libc_lseek (fd: fd, offset: offset, SEEK_SET) == (off_t) -1) |
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| 38 | return -1; |
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| 39 | |
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| 40 | /* Write out the data. */ |
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| 41 | result = __libc_read (fd, buf, nbyte); |
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| 42 | |
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| 43 | /* Now we have to restore the position. If this fails we have to |
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| 44 | return this as an error. But if the writing also failed we |
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| 45 | return this error. */ |
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| 46 | save_errno = errno; |
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| 47 | if (__libc_lseek (fd: fd, offset: old_offset, SEEK_SET) == (off_t) -1) |
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| 48 | { |
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| 49 | if (result == -1) |
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| 50 | __set_errno (save_errno); |
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| 51 | return -1; |
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| 52 | } |
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| 53 | __set_errno (save_errno); |
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| 54 | |
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| 55 | return result; |
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| 56 | } |
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| 57 | |
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| 58 | #ifndef __libc_pread |
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| 59 | strong_alias (__libc_pread, __pread) |
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| 60 | weak_alias (__libc_pread, pread) |
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| 61 | #endif |
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| 62 | |
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