66 lines
2.0 KiB
C
66 lines
2.0 KiB
C
/* replacement pread function
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Copyright (C) 2009-2024 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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/* Specification. */
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#include <unistd.h>
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#include <errno.h>
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#define __libc_lseek(f,o,w) lseek (f, o, w)
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#define __set_errno(Val) errno = (Val)
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#define __libc_read(f,b,n) read (f, b, n)
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/* pread substitute for systems that the function, such as mingw32 and BeOS. */
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/* The following is identical to the function from glibc's
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sysdeps/posix/pread.c */
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/* Note: This implementation of pread is not multithread-safe. */
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ssize_t
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pread (int fd, void *buf, size_t nbyte, off_t offset)
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{
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/* Since we must not change the file pointer preserve the value so that
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we can restore it later. */
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int saved_errno;
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ssize_t result;
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off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
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if (old_offset == (off_t) -1)
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return -1;
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/* Set to wanted position. */
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if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
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return -1;
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/* Write out the data. */
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result = __libc_read (fd, buf, nbyte);
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/* Now we have to restore the position. If this fails we have to
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return this as an error. But if the writing also failed we
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return this error. */
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saved_errno = errno;
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if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
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{
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if (result == -1)
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__set_errno (saved_errno);
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return -1;
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}
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__set_errno (saved_errno);
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return result;
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}
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