The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_syscalls.c

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    1 /*-
    2  * Copyright (c) 1999 Assar Westerlund
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD$");
   29 
   30 #include <sys/param.h>
   31 #include <sys/kernel.h>
   32 #include <sys/lock.h>
   33 #include <sys/module.h>
   34 #include <sys/mutex.h>
   35 #include <sys/proc.h>
   36 #include <sys/resourcevar.h>
   37 #include <sys/sx.h>
   38 #include <sys/syscall.h>
   39 #include <sys/sysent.h>
   40 #include <sys/sysproto.h>
   41 #include <sys/systm.h>
   42 #include <machine/atomic.h>
   43 
   44 /*
   45  * Acts like "nosys" but can be identified in sysent for dynamic call
   46  * number assignment for a limited number of calls.
   47  *
   48  * Place holder for system call slots reserved for loadable modules.
   49  */
   50 int
   51 lkmnosys(struct thread *td, struct nosys_args *args)
   52 {
   53 
   54         return (nosys(td, args));
   55 }
   56 
   57 int
   58 lkmressys(struct thread *td, struct nosys_args *args)
   59 {
   60 
   61         return (nosys(td, args));
   62 }
   63 
   64 static void
   65 syscall_thread_drain(struct sysent *se)
   66 {
   67         u_int32_t cnt, oldcnt;
   68 
   69         do {
   70                 oldcnt = se->sy_thrcnt;
   71                 KASSERT((oldcnt & SY_THR_STATIC) == 0,
   72                     ("drain on static syscall"));
   73                 cnt = oldcnt | SY_THR_DRAINING;
   74         } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
   75         while (atomic_cmpset_32(&se->sy_thrcnt, SY_THR_DRAINING,
   76             SY_THR_ABSENT) == 0)
   77                 pause("scdrn", hz/2);
   78 }
   79 
   80 int
   81 syscall_thread_enter(struct thread *td, struct sysent *se)
   82 {
   83         u_int32_t cnt, oldcnt;
   84 
   85         do {
   86                 oldcnt = se->sy_thrcnt;
   87                 if ((oldcnt & SY_THR_STATIC) != 0)
   88                         return (0);
   89                 if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0)
   90                         return (ENOSYS);
   91                 cnt = oldcnt + SY_THR_INCR;
   92         } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
   93         return (0);
   94 }
   95 
   96 void
   97 syscall_thread_exit(struct thread *td, struct sysent *se)
   98 {
   99         u_int32_t cnt, oldcnt;
  100 
  101         do {
  102                 oldcnt = se->sy_thrcnt;
  103                 if ((oldcnt & SY_THR_STATIC) != 0)
  104                         return;
  105                 cnt = oldcnt - SY_THR_INCR;
  106         } while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
  107 }
  108 
  109 int
  110 syscall_register(int *offset, struct sysent *new_sysent,
  111     struct sysent *old_sysent, int flags)
  112 {
  113         int i;
  114 
  115         if ((flags & ~SY_THR_STATIC) != 0)
  116                 return (EINVAL);
  117 
  118         if (*offset == NO_SYSCALL) {
  119                 for (i = 1; i < SYS_MAXSYSCALL; ++i)
  120                         if (sysent[i].sy_call == (sy_call_t *)lkmnosys)
  121                                 break;
  122                 if (i == SYS_MAXSYSCALL)
  123                         return (ENFILE);
  124                 *offset = i;
  125         } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL)
  126                 return (EINVAL);
  127         else if (sysent[*offset].sy_call != (sy_call_t *)lkmnosys &&
  128             sysent[*offset].sy_call != (sy_call_t *)lkmressys)
  129                 return (EEXIST);
  130 
  131         KASSERT(sysent[*offset].sy_thrcnt == SY_THR_ABSENT,
  132             ("dynamic syscall is not protected"));
  133         *old_sysent = sysent[*offset];
  134         new_sysent->sy_thrcnt = SY_THR_ABSENT;
  135         sysent[*offset] = *new_sysent;
  136         atomic_store_rel_32(&sysent[*offset].sy_thrcnt, flags);
  137         return (0);
  138 }
  139 
  140 int
  141 syscall_deregister(int *offset, struct sysent *old_sysent)
  142 {
  143         struct sysent *se;
  144 
  145         if (*offset == 0)
  146                 return (0); /* XXX? */
  147 
  148         se = &sysent[*offset];
  149         if ((se->sy_thrcnt & SY_THR_STATIC) != 0)
  150                 return (EINVAL);
  151         syscall_thread_drain(se);
  152         sysent[*offset] = *old_sysent;
  153         return (0);
  154 }
  155 
  156 int
  157 syscall_module_handler(struct module *mod, int what, void *arg)
  158 {
  159         struct syscall_module_data *data = arg;
  160         modspecific_t ms;
  161         int error;
  162 
  163         switch (what) {
  164         case MOD_LOAD:
  165                 error = syscall_register(data->offset, data->new_sysent,
  166                     &data->old_sysent, data->flags);
  167                 if (error) {
  168                         /* Leave a mark so we know to safely unload below. */
  169                         data->offset = NULL;
  170                         return (error);
  171                 }
  172                 ms.intval = *data->offset;
  173                 MOD_XLOCK;
  174                 module_setspecific(mod, &ms);
  175                 MOD_XUNLOCK;
  176                 if (data->chainevh)
  177                         error = data->chainevh(mod, what, data->chainarg);
  178                 return (error);
  179         case MOD_UNLOAD:
  180                 /*
  181                  * MOD_LOAD failed, so just return without calling the
  182                  * chained handler since we didn't pass along the MOD_LOAD
  183                  * event.
  184                  */
  185                 if (data->offset == NULL)
  186                         return (0);
  187                 if (data->chainevh) {
  188                         error = data->chainevh(mod, what, data->chainarg);
  189                         if (error)
  190                                 return error;
  191                 }
  192                 error = syscall_deregister(data->offset, &data->old_sysent);
  193                 return (error);
  194         default:
  195                 if (data->chainevh)
  196                         return (data->chainevh(mod, what, data->chainarg));
  197                 return (EOPNOTSUPP);
  198         }
  199 
  200         /* NOTREACHED */
  201 }
  202 
  203 int
  204 syscall_helper_register(struct syscall_helper_data *sd, int flags)
  205 {
  206         struct syscall_helper_data *sd1;
  207         int error;
  208 
  209         for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
  210                 error = syscall_register(&sd1->syscall_no, &sd1->new_sysent,
  211                     &sd1->old_sysent, flags);
  212                 if (error != 0) {
  213                         syscall_helper_unregister(sd);
  214                         return (error);
  215                 }
  216                 sd1->registered = 1;
  217         }
  218         return (0);
  219 }
  220 
  221 int
  222 syscall_helper_unregister(struct syscall_helper_data *sd)
  223 {
  224         struct syscall_helper_data *sd1;
  225 
  226         for (sd1 = sd; sd1->registered != 0; sd1++) {
  227                 syscall_deregister(&sd1->syscall_no, &sd1->old_sysent);
  228                 sd1->registered = 0;
  229         }
  230         return (0);
  231 }

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