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: releng/8.4/sys/kern/kern_syscalls.c 215628 2010-11-21 12:40:16Z delphij $");
   29 
   30 #include <sys/param.h>
   31 #include <sys/lock.h>
   32 #include <sys/module.h>
   33 #include <sys/sx.h>
   34 #include <sys/syscall.h>
   35 #include <sys/sysent.h>
   36 #include <sys/sysproto.h>
   37 
   38 /*
   39  * Acts like "nosys" but can be identified in sysent for dynamic call
   40  * number assignment for a limited number of calls.
   41  *
   42  * Place holder for system call slots reserved for loadable modules.
   43  */
   44 int
   45 lkmnosys(struct thread *td, struct nosys_args *args)
   46 {
   47 
   48         return (nosys(td, args));
   49 }
   50 
   51 int
   52 lkmressys(struct thread *td, struct nosys_args *args)
   53 {
   54 
   55         return (nosys(td, args));
   56 }
   57 
   58 int
   59 syscall_register(int *offset, struct sysent *new_sysent,
   60     struct sysent *old_sysent)
   61 {
   62         int i;
   63 
   64         if (*offset == NO_SYSCALL) {
   65                 for (i = 1; i < SYS_MAXSYSCALL; ++i)
   66                         if (sysent[i].sy_call == (sy_call_t *)lkmnosys)
   67                                 break;
   68                 if (i == SYS_MAXSYSCALL)
   69                         return (ENFILE);
   70                 *offset = i;
   71         } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL)
   72                 return (EINVAL);
   73         else if (sysent[*offset].sy_call != (sy_call_t *)lkmnosys &&
   74             sysent[*offset].sy_call != (sy_call_t *)lkmressys)
   75                 return (EEXIST);
   76 
   77         *old_sysent = sysent[*offset];
   78         sysent[*offset] = *new_sysent;
   79         return (0);
   80 }
   81 
   82 int
   83 syscall_deregister(int *offset, struct sysent *old_sysent)
   84 {
   85 
   86         if (*offset)
   87                 sysent[*offset] = *old_sysent;
   88         return (0);
   89 }
   90 
   91 int
   92 syscall_module_handler(struct module *mod, int what, void *arg)
   93 {
   94         struct syscall_module_data *data = arg;
   95         modspecific_t ms;
   96         int error;
   97 
   98         switch (what) {
   99         case MOD_LOAD:
  100                 error = syscall_register(data->offset, data->new_sysent,
  101                     &data->old_sysent);
  102                 if (error) {
  103                         /* Leave a mark so we know to safely unload below. */
  104                         data->offset = NULL;
  105                         return (error);
  106                 }
  107                 ms.intval = *data->offset;
  108                 MOD_XLOCK;
  109                 module_setspecific(mod, &ms);
  110                 MOD_XUNLOCK;
  111                 if (data->chainevh)
  112                         error = data->chainevh(mod, what, data->chainarg);
  113                 return (error);
  114         case MOD_UNLOAD:
  115                 /*
  116                  * MOD_LOAD failed, so just return without calling the
  117                  * chained handler since we didn't pass along the MOD_LOAD
  118                  * event.
  119                  */
  120                 if (data->offset == NULL)
  121                         return (0);
  122                 if (data->chainevh) {
  123                         error = data->chainevh(mod, what, data->chainarg);
  124                         if (error)
  125                                 return error;
  126                 }
  127                 error = syscall_deregister(data->offset, &data->old_sysent);
  128                 return (error);
  129         default:
  130                 if (data->chainevh)
  131                         return (data->chainevh(mod, what, data->chainarg));
  132                 return (EOPNOTSUPP);
  133         }
  134 
  135         /* NOTREACHED */
  136 }
  137 
  138 int
  139 syscall_helper_register(struct syscall_helper_data *sd)
  140 {
  141         struct syscall_helper_data *sd1;
  142         int error;
  143 
  144         for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
  145                 error = syscall_register(&sd1->syscall_no, &sd1->new_sysent,
  146                     &sd1->old_sysent);
  147                 if (error != 0) {
  148                         syscall_helper_unregister(sd);
  149                         return (error);
  150                 }
  151                 sd1->registered = 1;
  152         }
  153         return (0);
  154 }
  155 
  156 int
  157 syscall_helper_unregister(struct syscall_helper_data *sd)
  158 {
  159         struct syscall_helper_data *sd1;
  160 
  161         for (sd1 = sd; sd1->registered != 0; sd1++) {
  162                 syscall_deregister(&sd1->syscall_no, &sd1->old_sysent);
  163                 sd1->registered = 0;
  164         }
  165         return (0);
  166 }

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