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Diffstat (limited to 'nis/lckcache.c')
| -rw-r--r-- | nis/lckcache.c | 181 |
1 files changed, 181 insertions, 0 deletions
diff --git a/nis/lckcache.c b/nis/lckcache.c new file mode 100644 index 0000000000..ead577372e --- /dev/null +++ b/nis/lckcache.c @@ -0,0 +1,181 @@ +/* Handle locking of NIS+ cache file. + Copyright (C) 1996 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Library General Public License as + published by the Free Software Foundation; either version 2 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. */ + +#include <fcntl.h> +#include <bits/libc-lock.h> +#include <shadow.h> +#include <signal.h> +#include <string.h> +#include <unistd.h> +#include <sys/file.h> +#include <rpcsvc/nis.h> +#include <rpcsvc/nislib.h> +#include <rpcsvc/nis_cache.h> + +/* How long to wait for getting the lock before returning with an + error. */ +#define TIMEOUT 15 /* sec */ + + +/* File descriptor for lock file. */ +static int lock_fd = -1; + +/* Prevent problems in multithreaded program by using mutex. */ +__libc_lock_define_initialized (static, lock) + + +/* Prototypes for local functions. */ +static void noop_handler __P ((int __sig)); + + +/* We cannot simply return in error cases. We have to close the file + and perhaps restore the signal handler. */ +#define RETURN_CLOSE_FD(code) \ + do { \ + if ((code) < 0 && lock_fd >= 0) \ + { \ + close (lock_fd); \ + lock_fd = -1; \ + } \ + __libc_lock_unlock (lock); \ + return (code); \ + } while (0) + +#define RETURN_RESTORE_HANDLER(code) \ + do { \ + /* Restore old action handler for alarm. We don't need to know \ + about the current one. */ \ + sigaction (SIGALRM, &saved_act, NULL); \ + RETURN_CLOSE_FD (code); \ + } while (0) + +#define RETURN_CLEAR_ALARM(code) \ + do { \ + /* Clear alarm. */ \ + alarm (0); \ + /* Restore old set of handled signals. We don't need to know \ + about the current one.*/ \ + sigprocmask (SIG_SETMASK, &saved_set, NULL); \ + RETURN_RESTORE_HANDLER (code); \ + } while (0) + + +int +__nis_lock_cache (void) +{ + int flags; + sigset_t saved_set; /* Saved set of caught signals. */ + struct sigaction saved_act; /* Saved signal action. */ + sigset_t new_set; /* New set of caught signals. */ + struct sigaction new_act; /* New signal action. */ + struct flock fl; /* Information struct for locking. */ + int result; + + if (lock_fd != -1) + /* Still locked by own process. */ + return -1; + + /* Prevent problems caused by multiple threads. */ + __libc_lock_lock (lock); + + lock_fd = open (CACHELOCK, O_RDONLY|O_CREAT, 0666); + if (lock_fd == -1) + /* Cannot create lock file. */ + RETURN_CLOSE_FD (-1); + + /* Make sure file gets correctly closed when process finished. */ + flags = fcntl (lock_fd, F_GETFD, 0); + if (flags == -1) + /* Cannot get file flags. */ + RETURN_CLOSE_FD (-1); + flags |= FD_CLOEXEC; /* Close on exit. */ + if (fcntl (lock_fd, F_SETFD, flags) < 0) + /* Cannot set new flags. */ + RETURN_CLOSE_FD (-1); + + /* Now we have to get exclusive write access. Since multiple + process could try this we won't stop when it first fails. + Instead we set a timeout for the system call. Once the timer + expires it is likely that there are some problems which cannot be + resolved by waiting. + + It is important that we don't change the signal state. We must + restore the old signal behaviour. */ + memset (&new_act, '\0', sizeof (struct sigaction)); + new_act.sa_handler = noop_handler; + sigfillset (&new_act.sa_mask); + new_act.sa_flags = 0ul; + + /* Install new action handler for alarm and save old. */ + if (sigaction (SIGALRM, &new_act, &saved_act) < 0) + /* Cannot install signal handler. */ + RETURN_CLOSE_FD (-1); + + /* Now make sure the alarm signal is not blocked. */ + sigemptyset (&new_set); + sigaddset (&new_set, SIGALRM); + if (sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0) + RETURN_RESTORE_HANDLER (-1); + + /* Start timer. If we cannot get the lock in the specified time we + get a signal. */ + alarm (TIMEOUT); + + /* Try to get the lock. */ + memset (&fl, '\0', sizeof (struct flock)); + fl.l_type = F_RDLCK; + fl.l_whence = SEEK_SET; + result = fcntl (lock_fd, F_SETLK, &fl); + + RETURN_CLEAR_ALARM (result); +} + + +int +__nis_unlock_cache () +{ + int result; + + if (lock_fd == -1) + /* There is no lock set. */ + result = -1; + else + { + /* Prevent problems caused by multiple threads. */ + __libc_lock_lock (lock); + + result = close (lock_fd); + + /* Mark descriptor as unused. */ + lock_fd = -1; + + /* Clear mutex. */ + __libc_lock_unlock (lock); + } + + return result; +} + + +static void +noop_handler (sig) + int sig; +{ + /* We simply return which makes the `fcntl' call return with an error. */ +} |