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63 lines
2.0 KiB
C
63 lines
2.0 KiB
C
/* Read block from given position in file without changing file pointer.
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POSIX version.
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Copyright (C) 1997-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <unistd.h>
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/* Note: This implementation of pread is not multithread-safe. */
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ssize_t
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__libc_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 save_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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save_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 (save_errno);
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return -1;
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}
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__set_errno (save_errno);
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return result;
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}
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#ifndef __libc_pread
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strong_alias (__libc_pread, __pread)
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weak_alias (__libc_pread, pread)
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#endif
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