0d5b291753
Commit 06ab719d30
("Fix Linux fcntl OFD
locks for non-LFS architectures (BZ#20251)") introduced the use of
fcntl64 into the utmp implementation. However, the lock file
structure was not updated to struct flock64 at that point.
490 lines
11 KiB
C
490 lines
11 KiB
C
/* Copyright (C) 1996-2019 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>
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and Paul Janzen <pcj@primenet.com>, 1996.
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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 <assert.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <utmp.h>
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#include <not-cancel.h>
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#include <kernel-features.h>
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#include <sigsetops.h>
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#include <not-cancel.h>
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#include "utmp-private.h"
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#include "utmp-equal.h"
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/* Descriptor for the file and position. */
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static int file_fd = -1;
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static bool file_writable;
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static off64_t file_offset;
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/* Cache for the last read entry. */
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static struct utmp last_entry;
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/* Locking timeout. */
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#ifndef TIMEOUT
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# define TIMEOUT 10
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#endif
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/* Do-nothing handler for locking timeout. */
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static void timeout_handler (int signum) {};
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/* try_file_lock (LOCKING, FD, TYPE) returns true if the locking
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operation failed and recovery needs to be performed.
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file_unlock (FD) removes the lock (which must have been
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successfully acquired). */
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static bool
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try_file_lock (int fd, int type)
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{
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/* Cancel any existing alarm. */
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int old_timeout = alarm (0);
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/* Establish signal handler. */
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struct sigaction old_action;
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struct sigaction action;
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action.sa_handler = timeout_handler;
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__sigemptyset (&action.sa_mask);
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action.sa_flags = 0;
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__sigaction (SIGALRM, &action, &old_action);
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alarm (TIMEOUT);
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/* Try to get the lock. */
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struct flock64 fl =
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{
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.l_type = type,
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fl.l_whence = SEEK_SET,
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};
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bool status = __fcntl64_nocancel (fd, F_SETLKW, &fl) < 0;
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int saved_errno = errno;
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/* Reset the signal handler and alarm. We must reset the alarm
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before resetting the handler so our alarm does not generate a
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spurious SIGALRM seen by the user. However, we cannot just set
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the user's old alarm before restoring the handler, because then
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it's possible our handler could catch the user alarm's SIGARLM and
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then the user would never see the signal he expected. */
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alarm (0);
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__sigaction (SIGALRM, &old_action, NULL);
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if (old_timeout != 0)
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alarm (old_timeout);
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__set_errno (saved_errno);
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return status;
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}
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static void
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file_unlock (int fd)
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{
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struct flock64 fl =
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{
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.l_type = F_UNLCK,
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};
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__fcntl64_nocancel (fd, F_SETLKW, &fl);
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}
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#ifndef TRANSFORM_UTMP_FILE_NAME
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# define TRANSFORM_UTMP_FILE_NAME(file_name) (file_name)
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#endif
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int
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__libc_setutent (void)
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{
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if (file_fd < 0)
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{
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const char *file_name;
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file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);
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file_writable = false;
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file_fd = __open_nocancel
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(file_name, O_RDONLY | O_LARGEFILE | O_CLOEXEC);
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if (file_fd == -1)
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return 0;
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}
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__lseek64 (file_fd, 0, SEEK_SET);
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file_offset = 0;
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/* Make sure the entry won't match. */
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last_entry.ut_type = -1;
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return 1;
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}
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/* Preform initialization if necessary. */
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static bool
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maybe_setutent (void)
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{
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return file_fd >= 0 || __libc_setutent ();
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}
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int
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__libc_getutent_r (struct utmp *buffer, struct utmp **result)
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{
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ssize_t nbytes;
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if (!maybe_setutent () || file_offset == -1l)
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{
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/* Not available. */
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*result = NULL;
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return -1;
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}
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if (try_file_lock (file_fd, F_RDLCK))
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nbytes = 0;
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else
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{
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/* Read the next entry. */
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nbytes = __read_nocancel (file_fd, &last_entry, sizeof (struct utmp));
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file_unlock (file_fd);
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}
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if (nbytes != sizeof (struct utmp))
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{
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if (nbytes != 0)
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file_offset = -1l;
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*result = NULL;
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return -1;
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}
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/* Update position pointer. */
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file_offset += sizeof (struct utmp);
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memcpy (buffer, &last_entry, sizeof (struct utmp));
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*result = buffer;
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return 0;
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}
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static int
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internal_getut_r (const struct utmp *id, struct utmp *buffer,
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bool *lock_failed)
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{
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int result = -1;
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if (try_file_lock (file_fd, F_RDLCK))
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{
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*lock_failed = true;
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return -1;
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}
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if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME
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|| id->ut_type == OLD_TIME || id->ut_type == NEW_TIME)
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{
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/* Search for next entry with type RUN_LVL, BOOT_TIME,
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OLD_TIME, or NEW_TIME. */
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while (1)
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{
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/* Read the next entry. */
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if (__read_nocancel (file_fd, buffer, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__set_errno (ESRCH);
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file_offset = -1l;
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goto unlock_return;
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}
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file_offset += sizeof (struct utmp);
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if (id->ut_type == buffer->ut_type)
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break;
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}
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}
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else
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{
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/* Search for the next entry with the specified ID and with type
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INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS. */
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while (1)
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{
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/* Read the next entry. */
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if (__read_nocancel (file_fd, buffer, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__set_errno (ESRCH);
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file_offset = -1l;
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goto unlock_return;
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}
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file_offset += sizeof (struct utmp);
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if (__utmp_equal (buffer, id))
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break;
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}
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}
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result = 0;
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unlock_return:
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file_unlock (file_fd);
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return result;
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}
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/* For implementing this function we don't use the getutent_r function
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because we can avoid the reposition on every new entry this way. */
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int
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__libc_getutid_r (const struct utmp *id, struct utmp *buffer,
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struct utmp **result)
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{
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if (!maybe_setutent () || file_offset == -1l)
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{
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*result = NULL;
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return -1;
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}
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/* We don't have to distinguish whether we can lock the file or
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whether there is no entry. */
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bool lock_failed = false;
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if (internal_getut_r (id, &last_entry, &lock_failed) < 0)
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{
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*result = NULL;
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return -1;
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}
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memcpy (buffer, &last_entry, sizeof (struct utmp));
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*result = buffer;
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return 0;
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}
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/* For implementing this function we don't use the getutent_r function
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because we can avoid the reposition on every new entry this way. */
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int
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__libc_getutline_r (const struct utmp *line, struct utmp *buffer,
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struct utmp **result)
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{
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if (!maybe_setutent () || file_offset == -1l)
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{
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*result = NULL;
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return -1;
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}
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if (try_file_lock (file_fd, F_RDLCK))
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{
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*result = NULL;
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return -1;
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}
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while (1)
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{
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/* Read the next entry. */
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if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__set_errno (ESRCH);
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file_offset = -1l;
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*result = NULL;
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goto unlock_return;
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}
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file_offset += sizeof (struct utmp);
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/* Stop if we found a user or login entry. */
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if ((last_entry.ut_type == USER_PROCESS
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|| last_entry.ut_type == LOGIN_PROCESS)
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&& (strncmp (line->ut_line, last_entry.ut_line, sizeof line->ut_line)
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== 0))
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break;
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}
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memcpy (buffer, &last_entry, sizeof (struct utmp));
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*result = buffer;
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unlock_return:
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file_unlock (file_fd);
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return ((*result == NULL) ? -1 : 0);
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}
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struct utmp *
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__libc_pututline (const struct utmp *data)
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{
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if (!maybe_setutent ())
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return NULL;
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struct utmp buffer;
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struct utmp *pbuf;
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int found;
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if (! file_writable)
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{
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/* We must make the file descriptor writable before going on. */
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const char *file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);
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int new_fd = __open_nocancel
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(file_name, O_RDWR | O_LARGEFILE | O_CLOEXEC);
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if (new_fd == -1)
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return NULL;
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if (__lseek64 (new_fd, __lseek64 (file_fd, 0, SEEK_CUR), SEEK_SET) == -1
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|| __dup2 (new_fd, file_fd) < 0)
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{
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__close_nocancel_nostatus (new_fd);
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return NULL;
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}
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__close_nocancel_nostatus (new_fd);
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file_writable = true;
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}
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/* Find the correct place to insert the data. */
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if (file_offset > 0
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&& ((last_entry.ut_type == data->ut_type
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&& (last_entry.ut_type == RUN_LVL
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|| last_entry.ut_type == BOOT_TIME
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|| last_entry.ut_type == OLD_TIME
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|| last_entry.ut_type == NEW_TIME))
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|| __utmp_equal (&last_entry, data)))
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found = 1;
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else
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{
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bool lock_failed = false;
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found = internal_getut_r (data, &buffer, &lock_failed);
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if (__builtin_expect (lock_failed, false))
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{
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__set_errno (EAGAIN);
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return NULL;
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}
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}
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if (try_file_lock (file_fd, F_WRLCK))
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return NULL;
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if (found < 0)
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{
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/* We append the next entry. */
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file_offset = __lseek64 (file_fd, 0, SEEK_END);
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if (file_offset % sizeof (struct utmp) != 0)
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{
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file_offset -= file_offset % sizeof (struct utmp);
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__ftruncate64 (file_fd, file_offset);
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if (__lseek64 (file_fd, 0, SEEK_END) < 0)
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{
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pbuf = NULL;
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goto unlock_return;
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}
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}
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}
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else
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{
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/* We replace the just read entry. */
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file_offset -= sizeof (struct utmp);
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__lseek64 (file_fd, file_offset, SEEK_SET);
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}
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/* Write the new data. */
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if (__write_nocancel (file_fd, data, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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/* If we appended a new record this is only partially written.
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Remove it. */
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if (found < 0)
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(void) __ftruncate64 (file_fd, file_offset);
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pbuf = NULL;
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}
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else
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{
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file_offset += sizeof (struct utmp);
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pbuf = (struct utmp *) data;
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}
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unlock_return:
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file_unlock (file_fd);
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return pbuf;
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}
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void
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__libc_endutent (void)
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{
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if (file_fd >= 0)
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{
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__close_nocancel_nostatus (file_fd);
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file_fd = -1;
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}
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}
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int
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__libc_updwtmp (const char *file, const struct utmp *utmp)
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{
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int result = -1;
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off64_t offset;
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int fd;
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/* Open WTMP file. */
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fd = __open_nocancel (file, O_WRONLY | O_LARGEFILE);
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if (fd < 0)
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return -1;
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if (try_file_lock (fd, F_WRLCK))
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{
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__close_nocancel_nostatus (fd);
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return -1;
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}
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/* Remember original size of log file. */
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offset = __lseek64 (fd, 0, SEEK_END);
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if (offset % sizeof (struct utmp) != 0)
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{
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offset -= offset % sizeof (struct utmp);
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__ftruncate64 (fd, offset);
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if (__lseek64 (fd, 0, SEEK_END) < 0)
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goto unlock_return;
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}
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/* Write the entry. If we can't write all the bytes, reset the file
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size back to the original size. That way, no partial entries
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will remain. */
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if (__write_nocancel (fd, utmp, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__ftruncate64 (fd, offset);
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goto unlock_return;
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}
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result = 0;
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unlock_return:
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file_unlock (fd);
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/* Close WTMP file. */
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__close_nocancel_nostatus (fd);
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return result;
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}
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