ipc/util.c

   1 /*
   2  * linux/ipc/util.c
   3  * Copyright (C) 1992 Krishna Balasubramanian
   4  *
   5  * Sep 1997 - Call suser() last after "normal" permission checks so we
   6  *            get BSD style process accounting right.
   7  *            Occurs in several places in the IPC code.
   8  *            Chris Evans, <chris@ferret.lmh.ox.ac.uk>
   9  * Nov 1999 - ipc helper functions, unified SMP locking
  10  *            Manfred Spraul <manfreds@colorfullife.com>
  11  * Oct 2002 - One lock per IPC id. RCU ipc_free for lock-free grow_ary().
  12  *            Mingming Cao <cmm@us.ibm.com>
  13  */
  14
  15 #include <linux/config.h>
  16 #include <linux/mm.h>
  17 #include <linux/shm.h>
  18 #include <linux/init.h>
  19 #include <linux/msg.h>
  20 #include <linux/smp_lock.h>
  21 #include <linux/vmalloc.h>
  22 #include <linux/slab.h>
  23 #include <linux/highuid.h>
  24 #include <linux/security.h>
  25 #include <linux/rcupdate.h>
  26 #include <linux/workqueue.h>
  27 #include <linux/seq_file.h>
  28 #include <linux/proc_fs.h>
  29
  30 #include <asm/unistd.h>
  31
  32 #include "util.h"
  33
  34 struct ipc_proc_iface {
  35         const char *path;
  36         const char *header;
  37         struct ipc_ids *ids;
  38         int (*show)(struct seq_file *, void *);
  39 };
  40
  41 /**
  42  *      ipc_init        -       initialise IPC subsystem
  43  *
  44  *      The various system5 IPC resources (semaphores, messages and shared
  45  *      memory are initialised
  46  */
  47
  48 static int __init ipc_init(void)
  49 {
  50         sem_init();
  51         msg_init();
  52         shm_init();
  53         return 0;
  54 }
  55 __initcall(ipc_init);
  56
  57 /**
  58  *      ipc_init_ids            -       initialise IPC identifiers
  59  *      @ids: Identifier set
  60  *      @size: Number of identifiers
  61  *
  62  *      Given a size for the ipc identifier range (limited below IPCMNI)
  63  *      set up the sequence range to use then allocate and initialise the
  64  *      array itself.
  65  */
  66
  67 void __init ipc_init_ids(struct ipc_ids* ids, int size)
  68 {
  69         int i;
  70         sema_init(&ids->sem,1);
  71
  72         if(size > IPCMNI)
  73                 size = IPCMNI;
  74         ids->in_use = 0;
  75         ids->max_id = -1;
  76         ids->seq = 0;
  77         {
  78                 int seq_limit = INT_MAX/SEQ_MULTIPLIER;
  79                 if(seq_limit > USHRT_MAX)
  80                         ids->seq_max = USHRT_MAX;
  81                  else
  82                         ids->seq_max = seq_limit;
  83         }
  84
  85         ids->entries = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*size +
  86                                      sizeof(struct ipc_id_ary));
  87
  88         if(ids->entries == NULL) {
  89                 printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
  90                 size = 0;
  91                 ids->entries = &ids->nullentry;
  92         }
  93         ids->entries->size = size;
  94         for(i=0;i<size;i++)
  95                 ids->entries->p[i] = NULL;
  96 }
  97
  98 #ifdef CONFIG_PROC_FS
  99 static struct file_operations sysvipc_proc_fops;
 100 /**
 101  *      ipc_init_proc_interface -  Create a proc interface for sysipc types
 102  *                                 using a seq_file interface.
 103  *      @path: Path in procfs
 104  *      @header: Banner to be printed at the beginning of the file.
 105  *      @ids: ipc id table to iterate.
 106  *      @show: show routine.
 107  */
 108 void __init ipc_init_proc_interface(const char *path, const char *header,
 109                                     struct ipc_ids *ids,
 110                                     int (*show)(struct seq_file *, void *))
 111 {
 112         struct proc_dir_entry *pde;
 113         struct ipc_proc_iface *iface;
 114
 115         iface = kmalloc(sizeof(*iface), GFP_KERNEL);
 116         if (!iface)
 117                 return;
 118         iface->path     = path;
 119         iface->header   = header;
 120         iface->ids      = ids;
 121         iface->show     = show;
 122
 123         pde = create_proc_entry(path,
 124                                 S_IRUGO,        /* world readable */
 125                                 NULL            /* parent dir */);
 126         if (pde) {
 127                 pde->data = iface;
 128                 pde->proc_fops = &sysvipc_proc_fops;
 129         } else {
 130                 kfree(iface);
 131         }
 132 }
 133 #endif
 134
 135 /**
 136  *      ipc_findkey     -       find a key in an ipc identifier set
 137  *      @ids: Identifier set
 138  *      @key: The key to find
 139  *
 140  *      Requires ipc_ids.sem locked.
 141  *      Returns the identifier if found or -1 if not.
 142  */
 143
 144 int ipc_findkey(struct ipc_ids* ids, key_t key)
 145 {
 146         int id;
 147         struct kern_ipc_perm* p;
 148         int max_id = ids->max_id;
 149
 150         /*
 151          * rcu_dereference() is not needed here
 152          * since ipc_ids.sem is held
 153          */
 154         for (id = 0; id <= max_id; id++) {
 155                 p = ids->entries->p[id];
 156                 if(p==NULL)
 157                         continue;
 158                 if (key == p->key)
 159                         return id;
 160         }
 161         return -1;
 162 }
 163
 164 /*
 165  * Requires ipc_ids.sem locked
 166  */
 167 static int grow_ary(struct ipc_ids* ids, int newsize)
 168 {
 169         struct ipc_id_ary* new;
 170         struct ipc_id_ary* old;
 171         int i;
 172         int size = ids->entries->size;
 173
 174         if(newsize > IPCMNI)
 175                 newsize = IPCMNI;
 176         if(newsize <= size)
 177                 return newsize;
 178
 179         new = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*newsize +
 180                             sizeof(struct ipc_id_ary));
 181         if(new == NULL)
 182                 return size;
 183         new->size = newsize;
 184         memcpy(new->p, ids->entries->p, sizeof(struct kern_ipc_perm *)*size +
 185                                         sizeof(struct ipc_id_ary));
 186         for(i=size;i<newsize;i++) {
 187                 new->p[i] = NULL;
 188         }
 189         old = ids->entries;
 190
 191         /*
 192          * Use rcu_assign_pointer() to make sure the memcpyed contents
 193          * of the new array are visible before the new array becomes visible.
 194          */
 195         rcu_assign_pointer(ids->entries, new);
 196
 197         ipc_rcu_putref(old);
 198         return newsize;
 199 }
 200
 201 /**
 202  *      ipc_addid       -       add an IPC identifier
 203  *      @ids: IPC identifier set
 204  *      @new: new IPC permission set
 205  *      @size: new size limit for the id array
 206  *
 207  *      Add an entry 'new' to the IPC arrays. The permissions object is
 208  *      initialised and the first free entry is set up and the id assigned
 209  *      is returned. The list is returned in a locked state on success.
 210  *      On failure the list is not locked and -1 is returned.
 211  *
 212  *      Called with ipc_ids.sem held.
 213  */
 214
 215 int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 216 {
 217         int id;
 218
 219         size = grow_ary(ids,size);
 220
 221         /*
 222          * rcu_dereference()() is not needed here since
 223          * ipc_ids.sem is held
 224          */
 225         for (id = 0; id < size; id++) {
 226                 if(ids->entries->p[id] == NULL)
 227                         goto found;
 228         }
 229         return -1;
 230 found:
 231         ids->in_use++;
 232         if (id > ids->max_id)
 233                 ids->max_id = id;
 234
 235         new->cuid = new->uid = current->euid;
 236         new->gid = new->cgid = current->egid;
 237
 238         new->seq = ids->seq++;
 239         if(ids->seq > ids->seq_max)
 240                 ids->seq = 0;
 241
 242         spin_lock_init(&new->lock);
 243         new->deleted = 0;
 244         rcu_read_lock();
 245         spin_lock(&new->lock);
 246         ids->entries->p[id] = new;
 247         return id;
 248 }
 249
 250 /**
 251  *      ipc_rmid        -       remove an IPC identifier
 252  *      @ids: identifier set
 253  *      @id: Identifier to remove
 254  *
 255  *      The identifier must be valid, and in use. The kernel will panic if
 256  *      fed an invalid identifier. The entry is removed and internal
 257  *      variables recomputed. The object associated with the identifier
 258  *      is returned.
 259  *      ipc_ids.sem and the spinlock for this ID is hold before this function
 260  *      is called, and remain locked on the exit.
 261  */
 262
 263 struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id)
 264 {
 265         struct kern_ipc_perm* p;
 266         int lid = id % SEQ_MULTIPLIER;
 267         if(lid >= ids->entries->size)
 268                 BUG();
 269
 270         /*
 271          * do not need a rcu_dereference()() here to force ordering
 272          * on Alpha, since the ipc_ids.sem is held.
 273          */
 274         p = ids->entries->p[lid];
 275         ids->entries->p[lid] = NULL;
 276         if(p==NULL)
 277                 BUG();
 278         ids->in_use--;
 279
 280         if (lid == ids->max_id) {
 281                 do {
 282                         lid--;
 283                         if(lid == -1)
 284                                 break;
 285                 } while (ids->entries->p[lid] == NULL);
 286                 ids->max_id = lid;
 287         }
 288         p->deleted = 1;
 289         return p;
 290 }
 291
 292 /**
 293  *      ipc_alloc       -       allocate ipc space
 294  *      @size: size desired
 295  *
 296  *      Allocate memory from the appropriate pools and return a pointer to it.
 297  *      NULL is returned if the allocation fails
 298  */
 299
 300 void* ipc_alloc(int size)
 301 {
 302         void* out;
 303         if(size > PAGE_SIZE)
 304                 out = vmalloc(size);
 305         else
 306                 out = kmalloc(size, GFP_KERNEL);
 307         return out;
 308 }
 309
 310 /**
 311  *      ipc_free        -       free ipc space
 312  *      @ptr: pointer returned by ipc_alloc
 313  *      @size: size of block
 314  *
 315  *      Free a block created with ipc_alloc. The caller must know the size
 316  *      used in the allocation call.
 317  */
 318
 319 void ipc_free(void* ptr, int size)
 320 {
 321         if(size > PAGE_SIZE)
 322                 vfree(ptr);
 323         else
 324                 kfree(ptr);
 325 }
 326
 327 /*
 328  * rcu allocations:
 329  * There are three headers that are prepended to the actual allocation:
 330  * - during use: ipc_rcu_hdr.
 331  * - during the rcu grace period: ipc_rcu_grace.
 332  * - [only if vmalloc]: ipc_rcu_sched.
 333  * Their lifetime doesn't overlap, thus the headers share the same memory.
 334  * Unlike a normal union, they are right-aligned, thus some container_of
 335  * forward/backward casting is necessary:
 336  */
 337 struct ipc_rcu_hdr
 338 {
 339         int refcount;
 340         int is_vmalloc;
 341         void *data[0];
 342 };
 343
 344
 345 struct ipc_rcu_grace
 346 {
 347         struct rcu_head rcu;
 348         /* "void *" makes sure alignment of following data is sane. */
 349         void *data[0];
 350 };
 351
 352 struct ipc_rcu_sched
 353 {
 354         struct work_struct work;
 355         /* "void *" makes sure alignment of following data is sane. */
 356         void *data[0];
 357 };
 358
 359 #define HDRLEN_KMALLOC          (sizeof(struct ipc_rcu_grace) > sizeof(struct ipc_rcu_hdr) ? \
 360                                         sizeof(struct ipc_rcu_grace) : sizeof(struct ipc_rcu_hdr))
 361 #define HDRLEN_VMALLOC          (sizeof(struct ipc_rcu_sched) > HDRLEN_KMALLOC ? \
 362                                         sizeof(struct ipc_rcu_sched) : HDRLEN_KMALLOC)
 363
 364 static inline int rcu_use_vmalloc(int size)
 365 {
 366         /* Too big for a single page? */
 367         if (HDRLEN_KMALLOC + size > PAGE_SIZE)
 368                 return 1;
 369         return 0;
 370 }
 371
 372 /**
 373  *      ipc_rcu_alloc   -       allocate ipc and rcu space
 374  *      @size: size desired
 375  *
 376  *      Allocate memory for the rcu header structure +  the object.
 377  *      Returns the pointer to the object.
 378  *      NULL is returned if the allocation fails.
 379  */
 380
 381 void* ipc_rcu_alloc(int size)
 382 {
 383         void* out;
 384         /*
 385          * We prepend the allocation with the rcu struct, and
 386          * workqueue if necessary (for vmalloc).
 387          */
 388         if (rcu_use_vmalloc(size)) {
 389                 out = vmalloc(HDRLEN_VMALLOC + size);
 390                 if (out) {
 391                         out += HDRLEN_VMALLOC;
 392                         container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 1;
 393                         container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
 394                 }
 395         } else {
 396                 out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
 397                 if (out) {
 398                         out += HDRLEN_KMALLOC;
 399                         container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 0;
 400                         container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
 401                 }
 402         }
 403
 404         return out;
 405 }
 406
 407 void ipc_rcu_getref(void *ptr)
 408 {
 409         container_of(ptr, struct ipc_rcu_hdr, data)->refcount++;
 410 }
 411
 412 /**
 413  * ipc_schedule_free - free ipc + rcu space
 414  * @head: RCU callback structure for queued work
 415  *
 416  * Since RCU callback function is called in bh,
 417  * we need to defer the vfree to schedule_work
 418  */
 419 static void ipc_schedule_free(struct rcu_head *head)
 420 {
 421         struct ipc_rcu_grace *grace =
 422                 container_of(head, struct ipc_rcu_grace, rcu);
 423         struct ipc_rcu_sched *sched =
 424                         container_of(&(grace->data[0]), struct ipc_rcu_sched, data[0]);
 425
 426         INIT_WORK(&sched->work, vfree, sched);
 427         schedule_work(&sched->work);
 428 }
 429
 430 /**
 431  * ipc_immediate_free - free ipc + rcu space
 432  * @head: RCU callback structure that contains pointer to be freed
 433  *
 434  * Free from the RCU callback context
 435  */
 436 static void ipc_immediate_free(struct rcu_head *head)
 437 {
 438         struct ipc_rcu_grace *free =
 439                 container_of(head, struct ipc_rcu_grace, rcu);
 440         kfree(free);
 441 }
 442
 443 void ipc_rcu_putref(void *ptr)
 444 {
 445         if (--container_of(ptr, struct ipc_rcu_hdr, data)->refcount > 0)
 446                 return;
 447
 448         if (container_of(ptr, struct ipc_rcu_hdr, data)->is_vmalloc) {
 449                 call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
 450                                 ipc_schedule_free);
 451         } else {
 452                 call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
 453                                 ipc_immediate_free);
 454         }
 455 }
 456
 457 /**
 458  *      ipcperms        -       check IPC permissions
 459  *      @ipcp: IPC permission set
 460  *      @flag: desired permission set.
 461  *
 462  *      Check user, group, other permissions for access
 463  *      to ipc resources. return 0 if allowed
 464  */
 465
 466 int ipcperms (struct kern_ipc_perm *ipcp, short flag)
 467 {       /* flag will most probably be 0 or S_...UGO from <linux/stat.h> */
 468         int requested_mode, granted_mode;
 469
 470         requested_mode = (flag >> 6) | (flag >> 3) | flag;
 471         granted_mode = ipcp->mode;
 472         if (current->euid == ipcp->cuid || current->euid == ipcp->uid)
 473                 granted_mode >>= 6;
 474         else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
 475                 granted_mode >>= 3;
 476         /* is there some bit set in requested_mode but not in granted_mode? */
 477         if ((requested_mode & ~granted_mode & 0007) &&
 478             !capable(CAP_IPC_OWNER))
 479                 return -1;
 480
 481         return security_ipc_permission(ipcp, flag);
 482 }
 483
 484 /*
 485  * Functions to convert between the kern_ipc_perm structure and the
 486  * old/new ipc_perm structures
 487  */
 488
 489 /**
 490  *      kernel_to_ipc64_perm    -       convert kernel ipc permissions to user
 491  *      @in: kernel permissions
 492  *      @out: new style IPC permissions
 493  *
 494  *      Turn the kernel object 'in' into a set of permissions descriptions
 495  *      for returning to userspace (out).
 496  */
 497
 498
 499 void kernel_to_ipc64_perm (struct kern_ipc_perm *in, struct ipc64_perm *out)
 500 {
 501         out->key        = in->key;
 502         out->uid        = in->uid;
 503         out->gid        = in->gid;
 504         out->cuid       = in->cuid;
 505         out->cgid       = in->cgid;
 506         out->mode       = in->mode;
 507         out->seq        = in->seq;
 508 }
 509
 510 /**
 511  *      ipc64_perm_to_ipc_perm  -       convert old ipc permissions to new
 512  *      @in: new style IPC permissions
 513  *      @out: old style IPC permissions
 514  *
 515  *      Turn the new style permissions object in into a compatibility
 516  *      object and store it into the 'out' pointer.
 517  */
 518
 519 void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
 520 {
 521         out->key        = in->key;
 522         SET_UID(out->uid, in->uid);
 523         SET_GID(out->gid, in->gid);
 524         SET_UID(out->cuid, in->cuid);
 525         SET_GID(out->cgid, in->cgid);
 526         out->mode       = in->mode;
 527         out->seq        = in->seq;
 528 }
 529
 530 /*
 531  * So far only shm_get_stat() calls ipc_get() via shm_get(), so ipc_get()
 532  * is called with shm_ids.sem locked.  Since grow_ary() is also called with
 533  * shm_ids.sem down(for Shared Memory), there is no need to add read
 534  * barriers here to gurantee the writes in grow_ary() are seen in order
 535  * here (for Alpha).
 536  *
 537  * However ipc_get() itself does not necessary require ipc_ids.sem down. So
 538  * if in the future ipc_get() is used by other places without ipc_ids.sem
 539  * down, then ipc_get() needs read memery barriers as ipc_lock() does.
 540  */
 541 struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
 542 {
 543         struct kern_ipc_perm* out;
 544         int lid = id % SEQ_MULTIPLIER;
 545         if(lid >= ids->entries->size)
 546                 return NULL;
 547         out = ids->entries->p[lid];
 548         return out;
 549 }
 550
 551 struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
 552 {
 553         struct kern_ipc_perm* out;
 554         int lid = id % SEQ_MULTIPLIER;
 555         struct ipc_id_ary* entries;
 556
 557         rcu_read_lock();
 558         entries = rcu_dereference(ids->entries);
 559         if(lid >= entries->size) {
 560                 rcu_read_unlock();
 561                 return NULL;
 562         }
 563         out = entries->p[lid];
 564         if(out == NULL) {
 565                 rcu_read_unlock();
 566                 return NULL;
 567         }
 568         spin_lock(&out->lock);
 569
 570         /* ipc_rmid() may have already freed the ID while ipc_lock
 571          * was spinning: here verify that the structure is still valid
 572          */
 573         if (out->deleted) {
 574                 spin_unlock(&out->lock);
 575                 rcu_read_unlock();
 576                 return NULL;
 577         }
 578         return out;
 579 }
 580
 581 void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
 582 {
 583         rcu_read_lock();
 584         spin_lock(&perm->lock);
 585 }
 586
 587 void ipc_unlock(struct kern_ipc_perm* perm)
 588 {
 589         spin_unlock(&perm->lock);
 590         rcu_read_unlock();
 591 }
 592
 593 int ipc_buildid(struct ipc_ids* ids, int id, int seq)
 594 {
 595         return SEQ_MULTIPLIER*seq + id;
 596 }
 597
 598 int ipc_checkid(struct ipc_ids* ids, struct kern_ipc_perm* ipcp, int uid)
 599 {
 600         if(uid/SEQ_MULTIPLIER != ipcp->seq)
 601                 return 1;
 602         return 0;
 603 }
 604
 605 #ifdef __ARCH_WANT_IPC_PARSE_VERSION
 606
 607
 608 /**
 609  *      ipc_parse_version       -       IPC call version
 610  *      @cmd: pointer to command
 611  *
 612  *      Return IPC_64 for new style IPC and IPC_OLD for old style IPC.
 613  *      The cmd value is turned from an encoding command and version into
 614  *      just the command code.
 615  */
 616
 617 int ipc_parse_version (int *cmd)
 618 {
 619         if (*cmd & IPC_64) {
 620                 *cmd ^= IPC_64;
 621                 return IPC_64;
 622         } else {
 623                 return IPC_OLD;
 624         }
 625 }
 626
 627 #endif /* __ARCH_WANT_IPC_PARSE_VERSION */
 628
 629 #ifdef CONFIG_PROC_FS
 630 static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
 631 {
 632         struct ipc_proc_iface *iface = s->private;
 633         struct kern_ipc_perm *ipc = it;
 634         loff_t p;
 635
 636         /* If we had an ipc id locked before, unlock it */
 637         if (ipc && ipc != SEQ_START_TOKEN)
 638                 ipc_unlock(ipc);
 639
 640         /*
 641          * p = *pos - 1 (because id 0 starts at position 1)
 642          *          + 1 (because we increment the position by one)
 643          */
 644         for (p = *pos; p <= iface->ids->max_id; p++) {
 645                 if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
 646                         *pos = p + 1;
 647                         return ipc;
 648                 }
 649         }
 650
 651         /* Out of range - return NULL to terminate iteration */
 652         return NULL;
 653 }
 654
 655 /*
 656  * File positions: pos 0 -> header, pos n -> ipc id + 1.
 657  * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
 658  */
 659 static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
 660 {
 661         struct ipc_proc_iface *iface = s->private;
 662         struct kern_ipc_perm *ipc;
 663         loff_t p;
 664
 665         /*
 666          * Take the lock - this will be released by the corresponding
 667          * call to stop().
 668          */
 669         down(&iface->ids->sem);
 670
 671         /* pos < 0 is invalid */
 672         if (*pos < 0)
 673                 return NULL;
 674
 675         /* pos == 0 means header */
 676         if (*pos == 0)
 677                 return SEQ_START_TOKEN;
 678
 679         /* Find the (pos-1)th ipc */
 680         for (p = *pos - 1; p <= iface->ids->max_id; p++) {
 681                 if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
 682                         *pos = p + 1;
 683                         return ipc;
 684                 }
 685         }
 686         return NULL;
 687 }
 688
 689 static void sysvipc_proc_stop(struct seq_file *s, void *it)
 690 {
 691         struct kern_ipc_perm *ipc = it;
 692         struct ipc_proc_iface *iface = s->private;
 693
 694         /* If we had a locked segment, release it */
 695         if (ipc && ipc != SEQ_START_TOKEN)
 696                 ipc_unlock(ipc);
 697
 698         /* Release the lock we took in start() */
 699         up(&iface->ids->sem);
 700 }
 701
 702 static int sysvipc_proc_show(struct seq_file *s, void *it)
 703 {
 704         struct ipc_proc_iface *iface = s->private;
 705
 706         if (it == SEQ_START_TOKEN)
 707                 return seq_puts(s, iface->header);
 708
 709         return iface->show(s, it);
 710 }
 711
 712 static struct seq_operations sysvipc_proc_seqops = {
 713         .start = sysvipc_proc_start,
 714         .stop  = sysvipc_proc_stop,
 715         .next  = sysvipc_proc_next,
 716         .show  = sysvipc_proc_show,
 717 };
 718
 719 static int sysvipc_proc_open(struct inode *inode, struct file *file) {
 720         int ret;
 721         struct seq_file *seq;
 722
 723         ret = seq_open(file, &sysvipc_proc_seqops);
 724         if (!ret) {
 725                 seq = file->private_data;
 726                 seq->private = PDE(inode)->data;
 727         }
 728         return ret;
 729 }
 730
 731 static struct file_operations sysvipc_proc_fops = {
 732         .open    = sysvipc_proc_open,
 733         .read    = seq_read,
 734         .llseek  = seq_lseek,
 735         .release = seq_release,
 736 };
 737 #endif /* CONFIG_PROC_FS */