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 <manfred@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  * Mar 2006 - support for audit of ipc object properties
  14  *            Dustin Kirkland <dustin.kirkland@us.ibm.com>
  15  */
  16
  17 #include <linux/config.h>
  18 #include <linux/mm.h>
  19 #include <linux/shm.h>
  20 #include <linux/init.h>
  21 #include <linux/msg.h>
  22 #include <linux/smp_lock.h>
  23 #include <linux/vmalloc.h>
  24 #include <linux/slab.h>
  25 #include <linux/capability.h>
  26 #include <linux/highuid.h>
  27 #include <linux/security.h>
  28 #include <linux/rcupdate.h>
  29 #include <linux/workqueue.h>
  30 #include <linux/seq_file.h>
  31 #include <linux/proc_fs.h>
  32 #include <linux/audit.h>
  33
  34 #include <asm/unistd.h>
  35
  36 #include "util.h"
  37
  38 struct ipc_proc_iface {
  39         const char *path;
  40         const char *header;
  41         struct ipc_ids *ids;
  42         int (*show)(struct seq_file *, void *);
  43 };
  44
  45 /**
  46  *      ipc_init        -       initialise IPC subsystem
  47  *
  48  *      The various system5 IPC resources (semaphores, messages and shared
  49  *      memory are initialised
  50  */
  51
  52 static int __init ipc_init(void)
  53 {
  54         sem_init();
  55         msg_init();
  56         shm_init();
  57         return 0;
  58 }
  59 __initcall(ipc_init);
  60
  61 /**
  62  *      ipc_init_ids            -       initialise IPC identifiers
  63  *      @ids: Identifier set
  64  *      @size: Number of identifiers
  65  *
  66  *      Given a size for the ipc identifier range (limited below IPCMNI)
  67  *      set up the sequence range to use then allocate and initialise the
  68  *      array itself.
  69  */
  70
  71 void __init ipc_init_ids(struct ipc_ids* ids, int size)
  72 {
  73         int i;
  74
  75         mutex_init(&ids->mutex);
  76
  77         if(size > IPCMNI)
  78                 size = IPCMNI;
  79         ids->in_use = 0;
  80         ids->max_id = -1;
  81         ids->seq = 0;
  82         {
  83                 int seq_limit = INT_MAX/SEQ_MULTIPLIER;
  84                 if(seq_limit > USHRT_MAX)
  85                         ids->seq_max = USHRT_MAX;
  86                  else
  87                         ids->seq_max = seq_limit;
  88         }
  89
  90         ids->entries = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*size +
  91                                      sizeof(struct ipc_id_ary));
  92
  93         if(ids->entries == NULL) {
  94                 printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
  95                 size = 0;
  96                 ids->entries = &ids->nullentry;
  97         }
  98         ids->entries->size = size;
  99         for(i=0;i<size;i++)
 100                 ids->entries->p[i] = NULL;
 101 }
 102
 103 #ifdef CONFIG_PROC_FS
 104 static struct file_operations sysvipc_proc_fops;
 105 /**
 106  *      ipc_init_proc_interface -  Create a proc interface for sysipc types
 107  *                                 using a seq_file interface.
 108  *      @path: Path in procfs
 109  *      @header: Banner to be printed at the beginning of the file.
 110  *      @ids: ipc id table to iterate.
 111  *      @show: show routine.
 112  */
 113 void __init ipc_init_proc_interface(const char *path, const char *header,
 114                                     struct ipc_ids *ids,
 115                                     int (*show)(struct seq_file *, void *))
 116 {
 117         struct proc_dir_entry *pde;
 118         struct ipc_proc_iface *iface;
 119
 120         iface = kmalloc(sizeof(*iface), GFP_KERNEL);
 121         if (!iface)
 122                 return;
 123         iface->path     = path;
 124         iface->header   = header;
 125         iface->ids      = ids;
 126         iface->show     = show;
 127
 128         pde = create_proc_entry(path,
 129                                 S_IRUGO,        /* world readable */
 130                                 NULL            /* parent dir */);
 131         if (pde) {
 132                 pde->data = iface;
 133                 pde->proc_fops = &sysvipc_proc_fops;
 134         } else {
 135                 kfree(iface);
 136         }
 137 }
 138 #endif
 139
 140 /**
 141  *      ipc_findkey     -       find a key in an ipc identifier set
 142  *      @ids: Identifier set
 143  *      @key: The key to find
 144  *
 145  *      Requires ipc_ids.mutex locked.
 146  *      Returns the identifier if found or -1 if not.
 147  */
 148
 149 int ipc_findkey(struct ipc_ids* ids, key_t key)
 150 {
 151         int id;
 152         struct kern_ipc_perm* p;
 153         int max_id = ids->max_id;
 154
 155         /*
 156          * rcu_dereference() is not needed here
 157          * since ipc_ids.mutex is held
 158          */
 159         for (id = 0; id <= max_id; id++) {
 160                 p = ids->entries->p[id];
 161                 if(p==NULL)
 162                         continue;
 163                 if (key == p->key)
 164                         return id;
 165         }
 166         return -1;
 167 }
 168
 169 /*
 170  * Requires ipc_ids.mutex locked
 171  */
 172 static int grow_ary(struct ipc_ids* ids, int newsize)
 173 {
 174         struct ipc_id_ary* new;
 175         struct ipc_id_ary* old;
 176         int i;
 177         int size = ids->entries->size;
 178
 179         if(newsize > IPCMNI)
 180                 newsize = IPCMNI;
 181         if(newsize <= size)
 182                 return newsize;
 183
 184         new = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*newsize +
 185                             sizeof(struct ipc_id_ary));
 186         if(new == NULL)
 187                 return size;
 188         new->size = newsize;
 189         memcpy(new->p, ids->entries->p, sizeof(struct kern_ipc_perm *)*size);
 190         for(i=size;i<newsize;i++) {
 191                 new->p[i] = NULL;
 192         }
 193         old = ids->entries;
 194
 195         /*
 196          * Use rcu_assign_pointer() to make sure the memcpyed contents
 197          * of the new array are visible before the new array becomes visible.
 198          */
 199         rcu_assign_pointer(ids->entries, new);
 200
 201         ipc_rcu_putref(old);
 202         return newsize;
 203 }
 204
 205 /**
 206  *      ipc_addid       -       add an IPC identifier
 207  *      @ids: IPC identifier set
 208  *      @new: new IPC permission set
 209  *      @size: new size limit for the id array
 210  *
 211  *      Add an entry 'new' to the IPC arrays. The permissions object is
 212  *      initialised and the first free entry is set up and the id assigned
 213  *      is returned. The list is returned in a locked state on success.
 214  *      On failure the list is not locked and -1 is returned.
 215  *
 216  *      Called with ipc_ids.mutex held.
 217  */
 218
 219 int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
 220 {
 221         int id;
 222
 223         size = grow_ary(ids,size);
 224
 225         /*
 226          * rcu_dereference()() is not needed here since
 227          * ipc_ids.mutex is held
 228          */
 229         for (id = 0; id < size; id++) {
 230                 if(ids->entries->p[id] == NULL)
 231                         goto found;
 232         }
 233         return -1;
 234 found:
 235         ids->in_use++;
 236         if (id > ids->max_id)
 237                 ids->max_id = id;
 238
 239         new->cuid = new->uid = current->euid;
 240         new->gid = new->cgid = current->egid;
 241
 242         new->seq = ids->seq++;
 243         if(ids->seq > ids->seq_max)
 244                 ids->seq = 0;
 245
 246         spin_lock_init(&new->lock);
 247         new->deleted = 0;
 248         rcu_read_lock();
 249         spin_lock(&new->lock);
 250         ids->entries->p[id] = new;
 251         return id;
 252 }
 253
 254 /**
 255  *      ipc_rmid        -       remove an IPC identifier
 256  *      @ids: identifier set
 257  *      @id: Identifier to remove
 258  *
 259  *      The identifier must be valid, and in use. The kernel will panic if
 260  *      fed an invalid identifier. The entry is removed and internal
 261  *      variables recomputed. The object associated with the identifier
 262  *      is returned.
 263  *      ipc_ids.mutex and the spinlock for this ID is hold before this function
 264  *      is called, and remain locked on the exit.
 265  */
 266
 267 struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id)
 268 {
 269         struct kern_ipc_perm* p;
 270         int lid = id % SEQ_MULTIPLIER;
 271         BUG_ON(lid >= ids->entries->size);
 272
 273         /*
 274          * do not need a rcu_dereference()() here to force ordering
 275          * on Alpha, since the ipc_ids.mutex is held.
 276          */
 277         p = ids->entries->p[lid];
 278         ids->entries->p[lid] = NULL;
 279         BUG_ON(p==NULL);
 280         ids->in_use--;
 281
 282         if (lid == ids->max_id) {
 283                 do {
 284                         lid--;
 285                         if(lid == -1)
 286                                 break;
 287                 } while (ids->entries->p[lid] == NULL);
 288                 ids->max_id = lid;
 289         }
 290         p->deleted = 1;
 291         return p;
 292 }
 293
 294 /**
 295  *      ipc_alloc       -       allocate ipc space
 296  *      @size: size desired
 297  *
 298  *      Allocate memory from the appropriate pools and return a pointer to it.
 299  *      NULL is returned if the allocation fails
 300  */
 301
 302 void* ipc_alloc(int size)
 303 {
 304         void* out;
 305         if(size > PAGE_SIZE)
 306                 out = vmalloc(size);
 307         else
 308                 out = kmalloc(size, GFP_KERNEL);
 309         return out;
 310 }
 311
 312 /**
 313  *      ipc_free        -       free ipc space
 314  *      @ptr: pointer returned by ipc_alloc
 315  *      @size: size of block
 316  *
 317  *      Free a block created with ipc_alloc. The caller must know the size
 318  *      used in the allocation call.
 319  */
 320
 321 void ipc_free(void* ptr, int size)
 322 {
 323         if(size > PAGE_SIZE)
 324                 vfree(ptr);
 325         else
 326                 kfree(ptr);
 327 }
 328
 329 /*
 330  * rcu allocations:
 331  * There are three headers that are prepended to the actual allocation:
 332  * - during use: ipc_rcu_hdr.
 333  * - during the rcu grace period: ipc_rcu_grace.
 334  * - [only if vmalloc]: ipc_rcu_sched.
 335  * Their lifetime doesn't overlap, thus the headers share the same memory.
 336  * Unlike a normal union, they are right-aligned, thus some container_of
 337  * forward/backward casting is necessary:
 338  */
 339 struct ipc_rcu_hdr
 340 {
 341         int refcount;
 342         int is_vmalloc;
 343         void *data[0];
 344 };
 345
 346
 347 struct ipc_rcu_grace
 348 {
 349         struct rcu_head rcu;
 350         /* "void *" makes sure alignment of following data is sane. */
 351         void *data[0];
 352 };
 353
 354 struct ipc_rcu_sched
 355 {
 356         struct work_struct work;
 357         /* "void *" makes sure alignment of following data is sane. */
 358         void *data[0];
 359 };
 360
 361 #define HDRLEN_KMALLOC          (sizeof(struct ipc_rcu_grace) > sizeof(struct ipc_rcu_hdr) ? \
 362                                         sizeof(struct ipc_rcu_grace) : sizeof(struct ipc_rcu_hdr))
 363 #define HDRLEN_VMALLOC          (sizeof(struct ipc_rcu_sched) > HDRLEN_KMALLOC ? \
 364                                         sizeof(struct ipc_rcu_sched) : HDRLEN_KMALLOC)
 365
 366 static inline int rcu_use_vmalloc(int size)
 367 {
 368         /* Too big for a single page? */
 369         if (HDRLEN_KMALLOC + size > PAGE_SIZE)
 370                 return 1;
 371         return 0;
 372 }
 373
 374 /**
 375  *      ipc_rcu_alloc   -       allocate ipc and rcu space
 376  *      @size: size desired
 377  *
 378  *      Allocate memory for the rcu header structure +  the object.
 379  *      Returns the pointer to the object.
 380  *      NULL is returned if the allocation fails.
 381  */
 382
 383 void* ipc_rcu_alloc(int size)
 384 {
 385         void* out;
 386         /*
 387          * We prepend the allocation with the rcu struct, and
 388          * workqueue if necessary (for vmalloc).
 389          */
 390         if (rcu_use_vmalloc(size)) {
 391                 out = vmalloc(HDRLEN_VMALLOC + size);
 392                 if (out) {
 393                         out += HDRLEN_VMALLOC;
 394                         container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 1;
 395                         container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
 396                 }
 397         } else {
 398                 out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
 399                 if (out) {
 400                         out += HDRLEN_KMALLOC;
 401                         container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 0;
 402                         container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
 403                 }
 404         }
 405
 406         return out;
 407 }
 408
 409 void ipc_rcu_getref(void *ptr)
 410 {
 411         container_of(ptr, struct ipc_rcu_hdr, data)->refcount++;
 412 }
 413
 414 /**
 415  * ipc_schedule_free - free ipc + rcu space
 416  * @head: RCU callback structure for queued work
 417  *
 418  * Since RCU callback function is called in bh,
 419  * we need to defer the vfree to schedule_work
 420  */
 421 static void ipc_schedule_free(struct rcu_head *head)
 422 {
 423         struct ipc_rcu_grace *grace =
 424                 container_of(head, struct ipc_rcu_grace, rcu);
 425         struct ipc_rcu_sched *sched =
 426                         container_of(&(grace->data[0]), struct ipc_rcu_sched, data[0]);
 427
 428         INIT_WORK(&sched->work, vfree, sched);
 429         schedule_work(&sched->work);
 430 }
 431
 432 /**
 433  * ipc_immediate_free - free ipc + rcu space
 434  * @head: RCU callback structure that contains pointer to be freed
 435  *
 436  * Free from the RCU callback context
 437  */
 438 static void ipc_immediate_free(struct rcu_head *head)
 439 {
 440         struct ipc_rcu_grace *free =
 441                 container_of(head, struct ipc_rcu_grace, rcu);
 442         kfree(free);
 443 }
 444
 445 void ipc_rcu_putref(void *ptr)
 446 {
 447         if (--container_of(ptr, struct ipc_rcu_hdr, data)->refcount > 0)
 448                 return;
 449
 450         if (container_of(ptr, struct ipc_rcu_hdr, data)->is_vmalloc) {
 451                 call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
 452                                 ipc_schedule_free);
 453         } else {
 454                 call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
 455                                 ipc_immediate_free);
 456         }
 457 }
 458
 459 /**
 460  *      ipcperms        -       check IPC permissions
 461  *      @ipcp: IPC permission set
 462  *      @flag: desired permission set.
 463  *
 464  *      Check user, group, other permissions for access
 465  *      to ipc resources. return 0 if allowed
 466  */
 467
 468 int ipcperms (struct kern_ipc_perm *ipcp, short flag)
 469 {       /* flag will most probably be 0 or S_...UGO from <linux/stat.h> */
 470         int requested_mode, granted_mode, err;
 471
 472         if (unlikely((err = audit_ipc_obj(ipcp))))
 473                 return err;
 474         requested_mode = (flag >> 6) | (flag >> 3) | flag;
 475         granted_mode = ipcp->mode;
 476         if (current->euid == ipcp->cuid || current->euid == ipcp->uid)
 477                 granted_mode >>= 6;
 478         else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
 479                 granted_mode >>= 3;
 480         /* is there some bit set in requested_mode but not in granted_mode? */
 481         if ((requested_mode & ~granted_mode & 0007) &&
 482             !capable(CAP_IPC_OWNER))
 483                 return -1;
 484
 485         return security_ipc_permission(ipcp, flag);
 486 }
 487
 488 /*
 489  * Functions to convert between the kern_ipc_perm structure and the
 490  * old/new ipc_perm structures
 491  */
 492
 493 /**
 494  *      kernel_to_ipc64_perm    -       convert kernel ipc permissions to user
 495  *      @in: kernel permissions
 496  *      @out: new style IPC permissions
 497  *
 498  *      Turn the kernel object 'in' into a set of permissions descriptions
 499  *      for returning to userspace (out).
 500  */
 501
 502
 503 void kernel_to_ipc64_perm (struct kern_ipc_perm *in, struct ipc64_perm *out)
 504 {
 505         out->key        = in->key;
 506         out->uid        = in->uid;
 507         out->gid        = in->gid;
 508         out->cuid       = in->cuid;
 509         out->cgid       = in->cgid;
 510         out->mode       = in->mode;
 511         out->seq        = in->seq;
 512 }
 513
 514 /**
 515  *      ipc64_perm_to_ipc_perm  -       convert old ipc permissions to new
 516  *      @in: new style IPC permissions
 517  *      @out: old style IPC permissions
 518  *
 519  *      Turn the new style permissions object in into a compatibility
 520  *      object and store it into the 'out' pointer.
 521  */
 522
 523 void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
 524 {
 525         out->key        = in->key;
 526         SET_UID(out->uid, in->uid);
 527         SET_GID(out->gid, in->gid);
 528         SET_UID(out->cuid, in->cuid);
 529         SET_GID(out->cgid, in->cgid);
 530         out->mode       = in->mode;
 531         out->seq        = in->seq;
 532 }
 533
 534 /*
 535  * So far only shm_get_stat() calls ipc_get() via shm_get(), so ipc_get()
 536  * is called with shm_ids.mutex locked.  Since grow_ary() is also called with
 537  * shm_ids.mutex down(for Shared Memory), there is no need to add read
 538  * barriers here to gurantee the writes in grow_ary() are seen in order
 539  * here (for Alpha).
 540  *
 541  * However ipc_get() itself does not necessary require ipc_ids.mutex down. So
 542  * if in the future ipc_get() is used by other places without ipc_ids.mutex
 543  * down, then ipc_get() needs read memery barriers as ipc_lock() does.
 544  */
 545 struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
 546 {
 547         struct kern_ipc_perm* out;
 548         int lid = id % SEQ_MULTIPLIER;
 549         if(lid >= ids->entries->size)
 550                 return NULL;
 551         out = ids->entries->p[lid];
 552         return out;
 553 }
 554
 555 struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
 556 {
 557         struct kern_ipc_perm* out;
 558         int lid = id % SEQ_MULTIPLIER;
 559         struct ipc_id_ary* entries;
 560
 561         rcu_read_lock();
 562         entries = rcu_dereference(ids->entries);
 563         if(lid >= entries->size) {
 564                 rcu_read_unlock();
 565                 return NULL;
 566         }
 567         out = entries->p[lid];
 568         if(out == NULL) {
 569                 rcu_read_unlock();
 570                 return NULL;
 571         }
 572         spin_lock(&out->lock);
 573
 574         /* ipc_rmid() may have already freed the ID while ipc_lock
 575          * was spinning: here verify that the structure is still valid
 576          */
 577         if (out->deleted) {
 578                 spin_unlock(&out->lock);
 579                 rcu_read_unlock();
 580                 return NULL;
 581         }
 582         return out;
 583 }
 584
 585 void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
 586 {
 587         rcu_read_lock();
 588         spin_lock(&perm->lock);
 589 }
 590
 591 void ipc_unlock(struct kern_ipc_perm* perm)
 592 {
 593         spin_unlock(&perm->lock);
 594         rcu_read_unlock();
 595 }
 596
 597 int ipc_buildid(struct ipc_ids* ids, int id, int seq)
 598 {
 599         return SEQ_MULTIPLIER*seq + id;
 600 }
 601
 602 int ipc_checkid(struct ipc_ids* ids, struct kern_ipc_perm* ipcp, int uid)
 603 {
 604         if(uid/SEQ_MULTIPLIER != ipcp->seq)
 605                 return 1;
 606         return 0;
 607 }
 608
 609 #ifdef __ARCH_WANT_IPC_PARSE_VERSION
 610
 611
 612 /**
 613  *      ipc_parse_version       -       IPC call version
 614  *      @cmd: pointer to command
 615  *
 616  *      Return IPC_64 for new style IPC and IPC_OLD for old style IPC.
 617  *      The cmd value is turned from an encoding command and version into
 618  *      just the command code.
 619  */
 620
 621 int ipc_parse_version (int *cmd)
 622 {
 623         if (*cmd & IPC_64) {
 624                 *cmd ^= IPC_64;
 625                 return IPC_64;
 626         } else {
 627                 return IPC_OLD;
 628         }
 629 }
 630
 631 #endif /* __ARCH_WANT_IPC_PARSE_VERSION */
 632
 633 #ifdef CONFIG_PROC_FS
 634 static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
 635 {
 636         struct ipc_proc_iface *iface = s->private;
 637         struct kern_ipc_perm *ipc = it;
 638         loff_t p;
 639
 640         /* If we had an ipc id locked before, unlock it */
 641         if (ipc && ipc != SEQ_START_TOKEN)
 642                 ipc_unlock(ipc);
 643
 644         /*
 645          * p = *pos - 1 (because id 0 starts at position 1)
 646          *          + 1 (because we increment the position by one)
 647          */
 648         for (p = *pos; p <= iface->ids->max_id; p++) {
 649                 if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
 650                         *pos = p + 1;
 651                         return ipc;
 652                 }
 653         }
 654
 655         /* Out of range - return NULL to terminate iteration */
 656         return NULL;
 657 }
 658
 659 /*
 660  * File positions: pos 0 -> header, pos n -> ipc id + 1.
 661  * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
 662  */
 663 static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
 664 {
 665         struct ipc_proc_iface *iface = s->private;
 666         struct kern_ipc_perm *ipc;
 667         loff_t p;
 668
 669         /*
 670          * Take the lock - this will be released by the corresponding
 671          * call to stop().
 672          */
 673         mutex_lock(&iface->ids->mutex);
 674
 675         /* pos < 0 is invalid */
 676         if (*pos < 0)
 677                 return NULL;
 678
 679         /* pos == 0 means header */
 680         if (*pos == 0)
 681                 return SEQ_START_TOKEN;
 682
 683         /* Find the (pos-1)th ipc */
 684         for (p = *pos - 1; p <= iface->ids->max_id; p++) {
 685                 if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
 686                         *pos = p + 1;
 687                         return ipc;
 688                 }
 689         }
 690         return NULL;
 691 }
 692
 693 static void sysvipc_proc_stop(struct seq_file *s, void *it)
 694 {
 695         struct kern_ipc_perm *ipc = it;
 696         struct ipc_proc_iface *iface = s->private;
 697
 698         /* If we had a locked segment, release it */
 699         if (ipc && ipc != SEQ_START_TOKEN)
 700                 ipc_unlock(ipc);
 701
 702         /* Release the lock we took in start() */
 703         mutex_unlock(&iface->ids->mutex);
 704 }
 705
 706 static int sysvipc_proc_show(struct seq_file *s, void *it)
 707 {
 708         struct ipc_proc_iface *iface = s->private;
 709
 710         if (it == SEQ_START_TOKEN)
 711                 return seq_puts(s, iface->header);
 712
 713         return iface->show(s, it);
 714 }
 715
 716 static struct seq_operations sysvipc_proc_seqops = {
 717         .start = sysvipc_proc_start,
 718         .stop  = sysvipc_proc_stop,
 719         .next  = sysvipc_proc_next,
 720         .show  = sysvipc_proc_show,
 721 };
 722
 723 static int sysvipc_proc_open(struct inode *inode, struct file *file) {
 724         int ret;
 725         struct seq_file *seq;
 726
 727         ret = seq_open(file, &sysvipc_proc_seqops);
 728         if (!ret) {
 729                 seq = file->private_data;
 730                 seq->private = PDE(inode)->data;
 731         }
 732         return ret;
 733 }
 734
 735 static struct file_operations sysvipc_proc_fops = {
 736         .open    = sysvipc_proc_open,
 737         .read    = seq_read,
 738         .llseek  = seq_lseek,
 739         .release = seq_release,
 740 };
 741 #endif /* CONFIG_PROC_FS */