nis/lckcache.c

   1 /* Handle locking of NIS+ cache file.
   2    Copyright (C) 1996, 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library and based on shadow/lckfile.c.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <fcntl.h>
  21 #include <bits/libc-lock.h>
  22 #include <shadow.h>
  23 #include <signal.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <sys/file.h>
  27 #include <rpcsvc/nis.h>
  28 #include <rpcsvc/nislib.h>
  29 #include <rpcsvc/nis_cache.h>
  30
  31 /* How long to wait for getting the lock before returning with an
  32    error.  */
  33 #define TIMEOUT 5 /* sec */
  34
  35
  36 /* File descriptor for lock file.  */
  37 static int lock_fd = -1;
  38
  39 /* Prevent problems in multithreaded program by using mutex.  */
  40 __libc_lock_define_initialized (static, lock)
  41
  42
  43 /* Prototypes for local functions.  */
  44 static void noop_handler __P ((int __sig));
  45
  46
  47 /* We cannot simply return in error cases.  We have to close the file
  48    and perhaps restore the signal handler.  */
  49 #define RETURN_CLOSE_FD(code)                                                 \
  50   do {                                                                        \
  51     if ((code) < 0 && lock_fd >= 0)                                           \
  52       {                                                                       \
  53         close (lock_fd);                                                      \
  54         lock_fd = -1;                                                         \
  55       }                                                                       \
  56     __libc_lock_unlock (lock);                                                \
  57     return (code);                                                            \
  58   } while (0)
  59
  60 #define RETURN_RESTORE_HANDLER(code)                                          \
  61   do {                                                                        \
  62     /* Restore old action handler for alarm.  We don't need to know           \
  63        about the current one.  */                                             \
  64     sigaction (SIGALRM, &saved_act, NULL);                                    \
  65     RETURN_CLOSE_FD (code);                                                   \
  66   } while (0)
  67
  68 #define RETURN_CLEAR_ALARM(code)                                              \
  69   do {                                                                        \
  70     /* Clear alarm.  */                                                       \
  71     alarm (0);                                                                \
  72     /* Restore old set of handled signals.  We don't need to know             \
  73        about the current one.*/                                               \
  74     sigprocmask (SIG_SETMASK, &saved_set, NULL);                              \
  75     RETURN_RESTORE_HANDLER (code);                                            \
  76   } while (0)
  77
  78
  79 int
  80 __nis_lock_cache (void)
  81 {
  82   int flags;
  83   sigset_t saved_set;                   /* Saved set of caught signals.  */
  84   struct sigaction saved_act;           /* Saved signal action.  */
  85   sigset_t new_set;                     /* New set of caught signals.  */
  86   struct sigaction new_act;             /* New signal action.  */
  87   struct flock fl;                      /* Information struct for locking.  */
  88   int result;
  89
  90   if (lock_fd != -1)
  91     /* Still locked by own process.  */
  92     return -1;
  93
  94   /* Prevent problems caused by multiple threads.  */
  95   __libc_lock_lock (lock);
  96
  97   lock_fd = open (CACHELOCK, O_RDONLY|O_CREAT, 0666);
  98   if (lock_fd == -1)
  99     /* Cannot create lock file.  */
 100     RETURN_CLOSE_FD (-1);
 101
 102   /* Make sure file gets correctly closed when process finished.  */
 103   flags = fcntl (lock_fd, F_GETFD, 0);
 104   if (flags == -1)
 105     /* Cannot get file flags.  */
 106     RETURN_CLOSE_FD (-1);
 107   flags |= FD_CLOEXEC;          /* Close on exit.  */
 108   if (fcntl (lock_fd, F_SETFD, flags) < 0)
 109     /* Cannot set new flags.  */
 110     RETURN_CLOSE_FD (-1);
 111
 112   /* Now we have to get exclusive write access.  Since multiple
 113      process could try this we won't stop when it first fails.
 114      Instead we set a timeout for the system call.  Once the timer
 115      expires it is likely that there are some problems which cannot be
 116      resolved by waiting.
 117
 118      It is important that we don't change the signal state.  We must
 119      restore the old signal behaviour.  */
 120   memset (&new_act, '\0', sizeof (struct sigaction));
 121   new_act.sa_handler = noop_handler;
 122   sigfillset (&new_act.sa_mask);
 123   new_act.sa_flags = 0ul;
 124
 125   /* Install new action handler for alarm and save old.  */
 126   if (sigaction (SIGALRM, &new_act, &saved_act) < 0)
 127     /* Cannot install signal handler.  */
 128     RETURN_CLOSE_FD (-1);
 129
 130   /* Now make sure the alarm signal is not blocked.  */
 131   sigemptyset (&new_set);
 132   sigaddset (&new_set, SIGALRM);
 133   if (sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
 134     RETURN_RESTORE_HANDLER (-1);
 135
 136   /* Start timer.  If we cannot get the lock in the specified time we
 137      get a signal.  */
 138   alarm (TIMEOUT);
 139
 140   /* Try to get the lock.  */
 141   memset (&fl, '\0', sizeof (struct flock));
 142   fl.l_type = F_RDLCK;
 143   fl.l_whence = SEEK_SET;
 144   result = fcntl (lock_fd, F_SETLKW, &fl);
 145
 146   RETURN_CLEAR_ALARM (result);
 147 }
 148
 149
 150 int
 151 __nis_unlock_cache ()
 152 {
 153   int result;
 154
 155   if (lock_fd == -1)
 156     /* There is no lock set.  */
 157     result = -1;
 158   else
 159     {
 160       /* Prevent problems caused by multiple threads.  */
 161       __libc_lock_lock (lock);
 162
 163       result = close (lock_fd);
 164
 165       /* Mark descriptor as unused.  */
 166       lock_fd = -1;
 167
 168       /* Clear mutex.  */
 169       __libc_lock_unlock (lock);
 170     }
 171
 172   return result;
 173 }
 174
 175
 176 static void
 177 noop_handler (sig)
 178      int sig;
 179 {
 180   /* We simply return which makes the `fcntl' call return with an error.  */
 181 }