servers/vfs/fscall.c

   1 /* This file handles nested counter-request calls to VFS sent by file system
   2  * (FS) servers in response to VFS requests.
   3  *
   4  * The entry points into this file are
   5  *   nested_fs_call     perform a nested call from a file system server
   6  */
   7
   8 #include "fs.h"
   9 #include "fproc.h"
  10 #include <string.h>
  11 #include <assert.h>
  12 #include <minix/callnr.h>
  13 #include <minix/endpoint.h>
  14
  15 /* maximum nested call stack depth */
  16 #define MAX_DEPTH 1
  17
  18 /* global variables stack */
  19 PRIVATE struct {
  20   struct fproc *g_fp;                   /* pointer to caller process */
  21   message g_m_in;                       /* request message */
  22   message g_m_out;                      /* reply message */
  23   int g_who_e;                          /* endpoint of caller process */
  24   int g_who_p;                          /* slot number of caller process */
  25   int g_call_nr;                        /* call number */
  26   int g_super_user;                     /* is the caller root? */
  27   char g_user_fullpath[PATH_MAX+1];     /* path to look up */
  28 } globals[MAX_DEPTH];
  29
  30 PRIVATE int depth = 0;                  /* current globals stack level */
  31
  32 #if ENABLE_SYSCALL_STATS
  33 EXTERN unsigned long calls_stats[NCALLS];
  34 #endif
  35
  36 FORWARD _PROTOTYPE( int push_globals, (void)                            );
  37 FORWARD _PROTOTYPE( void pop_globals, (void)                            );
  38 FORWARD _PROTOTYPE( void set_globals, (message *m)                      );
  39
  40 /*===========================================================================*
  41  *                              push_globals                                 *
  42  *===========================================================================*/
  43 PRIVATE int push_globals()
  44 {
  45 /* Save the global variables of the current call onto the globals stack.
  46  */
  47
  48   if (depth == MAX_DEPTH)
  49         return EPERM;
  50
  51   globals[depth].g_fp = fp;
  52   globals[depth].g_m_in = m_in;
  53   globals[depth].g_m_out = m_out;
  54   globals[depth].g_who_e = who_e;
  55   globals[depth].g_who_p = who_p;
  56   globals[depth].g_call_nr = call_nr;
  57   globals[depth].g_super_user = super_user;
  58
  59   /* XXX is it safe to strcpy this? */
  60   assert(sizeof(globals[0].g_user_fullpath) == sizeof(user_fullpath));
  61   memcpy(globals[depth].g_user_fullpath, user_fullpath, sizeof(user_fullpath));
  62
  63   /* err_code is not used across blocking calls */
  64
  65   depth++;
  66
  67   return OK;
  68 }
  69
  70 /*===========================================================================*
  71  *                              pop_globals                                  *
  72  *===========================================================================*/
  73 PRIVATE void pop_globals()
  74 {
  75 /* Restore the global variables of a call from the globals stack.
  76  */
  77
  78   if (depth == 0)
  79         panic("VFS", "Popping from empty globals stack!", NO_NUM);
  80
  81   depth--;
  82
  83   fp = globals[depth].g_fp;
  84   m_in = globals[depth].g_m_in;
  85   m_out = globals[depth].g_m_out;
  86   who_e = globals[depth].g_who_e;
  87   who_p = globals[depth].g_who_p;
  88   call_nr = globals[depth].g_call_nr;
  89   super_user = globals[depth].g_super_user;
  90
  91   memcpy(user_fullpath, globals[depth].g_user_fullpath, sizeof(user_fullpath));
  92 }
  93
  94 /*===========================================================================*
  95  *                              set_globals                                  *
  96  *===========================================================================*/
  97 PRIVATE void set_globals(m)
  98 message *m;                             /* request message */
  99 {
 100 /* Initialize global variables based on a request message.
 101  */
 102
 103   m_in = *m;
 104   who_e = m_in.m_source;
 105   who_p = _ENDPOINT_P(who_e);
 106   call_nr = m_in.m_type;
 107   fp = &fproc[who_p];
 108   super_user = (fp->fp_effuid == SU_UID ? TRUE : FALSE);
 109   /* the rest need not be initialized */
 110 }
 111
 112 /*===========================================================================*
 113  *                              nested_fs_call                               *
 114  *===========================================================================*/
 115 PUBLIC void nested_fs_call(m)
 116 message *m;                             /* request/reply message pointer */
 117 {
 118 /* Handle a nested call from a file system server.
 119  */
 120   int r;
 121
 122   /* Save global variables of the current call */
 123   if ((r = push_globals()) != OK) {
 124         printf("VFS: error saving global variables in call %d from FS %d\n",
 125                 m->m_type, m->m_source);
 126   } else {
 127         /* Initialize global variables for the nested call */
 128         set_globals(m);
 129
 130         /* Perform the nested call */
 131         if (call_nr < 0 || call_nr >= NCALLS) {
 132                 printf("VFS: invalid nested call %d from FS %d\n", call_nr,
 133                         who_e);
 134
 135                 r = ENOSYS;
 136         } else {
 137 #if ENABLE_SYSCALL_STATS
 138                 calls_stats[call_nr]++;
 139 #endif
 140
 141                 r = (*call_vec[call_nr])();
 142         }
 143
 144         /* Store the result, and restore original global variables */
 145         *m = m_out;
 146
 147         pop_globals();
 148   }
 149
 150   m->m_type = r;
 151 }