1 /* replacement pread function 2 Copyright (C) 2009-2021 Free Software Foundation, Inc. 3 4 This file is free software: you can redistribute it and/or modify 5 it under the terms of the GNU Lesser General Public License as 6 published by the Free Software Foundation; either version 2.1 of the 7 License, or (at your option) any later version. 8 9 This file 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 12 GNU Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public License 15 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 16 17 #include <config.h> 18 19 /* Specification. */ 20 #include <unistd.h> 21 22 #include <errno.h> 23 24 #define __libc_lseek(f,o,w) lseek (f, o, w) 25 #define __set_errno(Val) errno = (Val) 26 #define __libc_read(f,b,n) read (f, b, n) 27 28 /* pread substitute for systems that the function, such as mingw32 and BeOS. */ 29 /* The following is identical to the function from glibc's 30 sysdeps/posix/pread.c */ 31 32 /* Note: This implementation of pread is not multithread-safe. */ 33 34 ssize_t 35 pread (int fd, void *buf, size_t nbyte, off_t offset) /* */ 36 { 37 /* Since we must not change the file pointer preserve the value so that 38 we can restore it later. */ 39 int save_errno; 40 ssize_t result; 41 off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR); 42 if (old_offset == (off_t) -1) 43 return -1; 44 45 /* Set to wanted position. */ 46 if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1) 47 return -1; 48 49 /* Write out the data. */ 50 result = __libc_read (fd, buf, nbyte); 51 52 /* Now we have to restore the position. If this fails we have to 53 return this as an error. But if the writing also failed we 54 return this error. */ 55 save_errno = errno; 56 if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1) 57 { 58 if (result == -1) 59 __set_errno (save_errno); 60 return -1; 61 } 62 __set_errno (save_errno); 63 64 return result; 65 }