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

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