ipc/shm.c

   1 /*
   2  * linux/ipc/shm.c
   3  * Copyright (C) 1992, 1993 Krishna Balasubramanian
   4  *       Many improvements/fixes by Bruno Haible.
   5  * Replaced `struct shm_desc' by `struct vm_area_struct', July 1994.
   6  * Fixed the shm swap deallocation (shm_unuse()), August 1998 Andrea Arcangeli.
   7  *
   8  * /proc/sysvipc/shm support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
   9  * BIGMEM support, Andrea Arcangeli <andrea@suse.de>
  10  * SMP thread shm, Jean-Luc Boyard <jean-luc.boyard@siemens.fr>
  11  * HIGHMEM support, Ingo Molnar <mingo@redhat.com>
  12  * Make shmmax, shmall, shmmni sysctl'able, Christoph Rohland <cr@sap.com>
  13  * Shared /dev/zero support, Kanoj Sarcar <kanoj@sgi.com>
  14  * Move the mm functionality over to mm/shmem.c, Christoph Rohland <cr@sap.com>
  15  *
  16  */
  17
  18 #include <linux/config.h>
  19 #include <linux/malloc.h>
  20 #include <linux/shm.h>
  21 #include <linux/init.h>
  22 #include <linux/file.h>
  23 #include <linux/mman.h>
  24 #include <linux/proc_fs.h>
  25 #include <asm/uaccess.h>
  26
  27 #include "util.h"
  28
  29 struct shmid_kernel /* private to the kernel */
  30 {
  31         struct kern_ipc_perm    shm_perm;
  32         struct file *           shm_file;
  33         int                     id;
  34         unsigned long           shm_nattch;
  35         unsigned long           shm_segsz;
  36         time_t                  shm_atim;
  37         time_t                  shm_dtim;
  38         time_t                  shm_ctim;
  39         pid_t                   shm_cprid;
  40         pid_t                   shm_lprid;
  41 };
  42
  43 #define shm_flags       shm_perm.mode
  44
  45 static struct file_operations shm_file_operations;
  46 static struct vm_operations_struct shm_vm_ops;
  47
  48 static struct ipc_ids shm_ids;
  49
  50 #define shm_lock(id)    ((struct shmid_kernel*)ipc_lock(&shm_ids,id))
  51 #define shm_unlock(id)  ipc_unlock(&shm_ids,id)
  52 #define shm_lockall()   ipc_lockall(&shm_ids)
  53 #define shm_unlockall() ipc_unlockall(&shm_ids)
  54 #define shm_get(id)     ((struct shmid_kernel*)ipc_get(&shm_ids,id))
  55 #define shm_buildid(id, seq) \
  56         ipc_buildid(&shm_ids, id, seq)
  57
  58 static int newseg (key_t key, int shmflg, size_t size);
  59 static void shm_open (struct vm_area_struct *shmd);
  60 static void shm_close (struct vm_area_struct *shmd);
  61 #ifdef CONFIG_PROC_FS
  62 static int sysvipc_shm_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
  63 #endif
  64
  65 size_t  shm_ctlmax = SHMMAX;
  66 size_t  shm_ctlall = SHMALL;
  67 int     shm_ctlmni = SHMMNI;
  68
  69 static int shm_tot; /* total number of shared memory pages */
  70
  71 void __init shm_init (void)
  72 {
  73         ipc_init_ids(&shm_ids, 1);
  74         create_proc_read_entry("sysvipc/shm", 0, 0, sysvipc_shm_read_proc, NULL);
  75 }
  76
  77 static inline int shm_checkid(struct shmid_kernel *s, int id)
  78 {
  79         if (ipc_checkid(&shm_ids,&s->shm_perm,id))
  80                 return -EIDRM;
  81         return 0;
  82 }
  83
  84 static inline struct shmid_kernel *shm_rmid(int id)
  85 {
  86         return (struct shmid_kernel *)ipc_rmid(&shm_ids,id);
  87 }
  88
  89 static inline int shm_addid(struct shmid_kernel *shp)
  90 {
  91         return ipc_addid(&shm_ids, &shp->shm_perm, shm_ctlmni+1);
  92 }
  93
  94
  95
  96 static inline void shm_inc (int id) {
  97         struct shmid_kernel *shp;
  98
  99         if(!(shp = shm_lock(id)))
 100                 BUG();
 101         shp->shm_atim = CURRENT_TIME;
 102         shp->shm_lprid = current->pid;
 103         shp->shm_nattch++;
 104         shm_unlock(id);
 105 }
 106
 107 /* This is called by fork, once for every shm attach. */
 108 static void shm_open (struct vm_area_struct *shmd)
 109 {
 110         shm_inc (shmd->vm_file->f_dentry->d_inode->i_ino);
 111 }
 112
 113 /*
 114  * shm_destroy - free the struct shmid_kernel
 115  *
 116  * @shp: struct to free
 117  *
 118  * It has to be called with shp and shm_ids.sem locked
 119  */
 120 static void shm_destroy (struct shmid_kernel *shp)
 121 {
 122         shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
 123         shm_rmid (shp->id);
 124         fput (shp->shm_file);
 125         kfree (shp);
 126 }
 127
 128 /*
 129  * remove the attach descriptor shmd.
 130  * free memory for segment if it is marked destroyed.
 131  * The descriptor has already been removed from the current->mm->mmap list
 132  * and will later be kfree()d.
 133  */
 134 static void shm_close (struct vm_area_struct *shmd)
 135 {
 136         struct file * file = shmd->vm_file;
 137         int id = file->f_dentry->d_inode->i_ino;
 138         struct shmid_kernel *shp;
 139
 140         down (&shm_ids.sem);
 141         /* remove from the list of attaches of the shm segment */
 142         if(!(shp = shm_lock(id)))
 143                 BUG();
 144         shp->shm_lprid = current->pid;
 145         shp->shm_dtim = CURRENT_TIME;
 146         shp->shm_nattch--;
 147         if(shp->shm_nattch == 0 &&
 148            shp->shm_flags & SHM_DEST)
 149                 shm_destroy (shp);
 150
 151         shm_unlock(id);
 152         up (&shm_ids.sem);
 153 }
 154
 155 static int shm_mmap(struct file * file, struct vm_area_struct * vma)
 156 {
 157         UPDATE_ATIME(file->f_dentry->d_inode);
 158         vma->vm_ops = &shm_vm_ops;
 159         shm_inc(file->f_dentry->d_inode->i_ino);
 160         return 0;
 161 }
 162
 163 static struct file_operations shm_file_operations = {
 164         mmap:   shm_mmap
 165 };
 166
 167 static struct vm_operations_struct shm_vm_ops = {
 168         open:   shm_open,       /* callback for a new vm-area open */
 169         close:  shm_close,      /* callback for when the vm-area is released */
 170         nopage: shmem_nopage,
 171 };
 172
 173 static int newseg (key_t key, int shmflg, size_t size)
 174 {
 175         int error;
 176         struct shmid_kernel *shp;
 177         int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
 178         struct file * file;
 179         char name[13];
 180         int id;
 181
 182         if (size < SHMMIN || size > shm_ctlmax)
 183                 return -EINVAL;
 184
 185         if (shm_tot + numpages >= shm_ctlall)
 186                 return -ENOSPC;
 187
 188         shp = (struct shmid_kernel *) kmalloc (sizeof (*shp), GFP_USER);
 189         if (!shp)
 190                 return -ENOMEM;
 191         sprintf (name, "SYSV%08x", key);
 192         file = shmem_file_setup(name, size);
 193         error = PTR_ERR(file);
 194         if (IS_ERR(file))
 195                 goto no_file;
 196
 197         error = -ENOSPC;
 198         id = shm_addid(shp);
 199         if(id == -1)
 200                 goto no_id;
 201         shp->shm_perm.key = key;
 202         shp->shm_flags = (shmflg & S_IRWXUGO);
 203         shp->shm_cprid = current->pid;
 204         shp->shm_lprid = 0;
 205         shp->shm_atim = shp->shm_dtim = 0;
 206         shp->shm_ctim = CURRENT_TIME;
 207         shp->shm_segsz = size;
 208         shp->shm_nattch = 0;
 209         shp->id = shm_buildid(id,shp->shm_perm.seq);
 210         shp->shm_file = file;
 211         file->f_dentry->d_inode->i_ino = shp->id;
 212         file->f_op = &shm_file_operations;
 213         shm_tot += numpages;
 214         shm_unlock (id);
 215         return shp->id;
 216
 217 no_id:
 218         fput(file);
 219 no_file:
 220         kfree(shp);
 221         return error;
 222 }
 223
 224 asmlinkage long sys_shmget (key_t key, size_t size, int shmflg)
 225 {
 226         struct shmid_kernel *shp;
 227         int err, id = 0;
 228
 229         down(&shm_ids.sem);
 230         if (key == IPC_PRIVATE) {
 231                 err = newseg(key, shmflg, size);
 232         } else if ((id = ipc_findkey(&shm_ids, key)) == -1) {
 233                 if (!(shmflg & IPC_CREAT))
 234                         err = -ENOENT;
 235                 else
 236                         err = newseg(key, shmflg, size);
 237         } else if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) {
 238                 err = -EEXIST;
 239         } else {
 240                 shp = shm_lock(id);
 241                 if(shp==NULL)
 242                         BUG();
 243                 if (shp->shm_segsz < size)
 244                         err = -EINVAL;
 245                 else if (ipcperms(&shp->shm_perm, shmflg))
 246                         err = -EACCES;
 247                 else
 248                         err = shm_buildid(id, shp->shm_perm.seq);
 249                 shm_unlock(id);
 250         }
 251         up(&shm_ids.sem);
 252         return err;
 253 }
 254
 255 static inline unsigned long copy_shmid_to_user(void *buf, struct shmid64_ds *in, int version)
 256 {
 257         switch(version) {
 258         case IPC_64:
 259                 return copy_to_user(buf, in, sizeof(*in));
 260         case IPC_OLD:
 261             {
 262                 struct shmid_ds out;
 263
 264                 ipc64_perm_to_ipc_perm(&in->shm_perm, &out.shm_perm);
 265                 out.shm_segsz   = in->shm_segsz;
 266                 out.shm_atime   = in->shm_atime;
 267                 out.shm_dtime   = in->shm_dtime;
 268                 out.shm_ctime   = in->shm_ctime;
 269                 out.shm_cpid    = in->shm_cpid;
 270                 out.shm_lpid    = in->shm_lpid;
 271                 out.shm_nattch  = in->shm_nattch;
 272
 273                 return copy_to_user(buf, &out, sizeof(out));
 274             }
 275         default:
 276                 return -EINVAL;
 277         }
 278 }
 279
 280 struct shm_setbuf {
 281         uid_t   uid;
 282         gid_t   gid;
 283         mode_t  mode;
 284 };
 285
 286 static inline unsigned long copy_shmid_from_user(struct shm_setbuf *out, void *buf, int version)
 287 {
 288         switch(version) {
 289         case IPC_64:
 290             {
 291                 struct shmid64_ds tbuf;
 292
 293                 if (copy_from_user(&tbuf, buf, sizeof(tbuf)))
 294                         return -EFAULT;
 295
 296                 out->uid        = tbuf.shm_perm.uid;
 297                 out->gid        = tbuf.shm_perm.gid;
 298                 out->mode       = tbuf.shm_flags;
 299
 300                 return 0;
 301             }
 302         case IPC_OLD:
 303             {
 304                 struct shmid_ds tbuf_old;
 305
 306                 if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
 307                         return -EFAULT;
 308
 309                 out->uid        = tbuf_old.shm_perm.uid;
 310                 out->gid        = tbuf_old.shm_perm.gid;
 311                 out->mode       = tbuf_old.shm_flags;
 312
 313                 return 0;
 314             }
 315         default:
 316                 return -EINVAL;
 317         }
 318 }
 319
 320 static inline unsigned long copy_shminfo_to_user(void *buf, struct shminfo64 *in, int version)
 321 {
 322         switch(version) {
 323         case IPC_64:
 324                 return copy_to_user(buf, in, sizeof(*in));
 325         case IPC_OLD:
 326             {
 327                 struct shminfo out;
 328
 329                 if(in->shmmax > INT_MAX)
 330                         out.shmmax = INT_MAX;
 331                 else
 332                         out.shmmax = (int)in->shmmax;
 333
 334                 out.shmmin      = in->shmmin;
 335                 out.shmmni      = in->shmmni;
 336                 out.shmseg      = in->shmseg;
 337                 out.shmall      = in->shmall;
 338
 339                 return copy_to_user(buf, &out, sizeof(out));
 340             }
 341         default:
 342                 return -EINVAL;
 343         }
 344 }
 345
 346 static void shm_get_stat (unsigned long *rss, unsigned long *swp)
 347 {
 348         int i;
 349
 350         *rss = 0;
 351         *swp = 0;
 352
 353         for(i = 0; i <= shm_ids.max_id; i++) {
 354                 struct shmid_kernel* shp;
 355                 struct inode * inode;
 356
 357                 shp = shm_get(i);
 358                 if(shp == NULL)
 359                         continue;
 360                 inode = shp->shm_file->f_dentry->d_inode;
 361                 spin_lock (&inode->u.shmem_i.lock);
 362                 *rss += inode->i_mapping->nrpages;
 363                 *swp += inode->u.shmem_i.swapped;
 364                 spin_unlock (&inode->u.shmem_i.lock);
 365         }
 366 }
 367
 368 asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds *buf)
 369 {
 370         struct shm_setbuf setbuf;
 371         struct shmid_kernel *shp;
 372         int err, version;
 373
 374         if (cmd < 0 || shmid < 0)
 375                 return -EINVAL;
 376
 377         version = ipc_parse_version(&cmd);
 378
 379         switch (cmd) { /* replace with proc interface ? */
 380         case IPC_INFO:
 381         {
 382                 struct shminfo64 shminfo;
 383
 384                 memset(&shminfo,0,sizeof(shminfo));
 385                 shminfo.shmmni = shminfo.shmseg = shm_ctlmni;
 386                 shminfo.shmmax = shm_ctlmax;
 387                 shminfo.shmall = shm_ctlall;
 388
 389                 shminfo.shmmin = SHMMIN;
 390                 if(copy_shminfo_to_user (buf, &shminfo, version))
 391                         return -EFAULT;
 392                 /* reading a integer is always atomic */
 393                 err= shm_ids.max_id;
 394                 if(err<0)
 395                         err = 0;
 396                 return err;
 397         }
 398         case SHM_INFO:
 399         {
 400                 struct shm_info shm_info;
 401
 402                 memset(&shm_info,0,sizeof(shm_info));
 403                 down(&shm_ids.sem);
 404                 shm_lockall();
 405                 shm_info.used_ids = shm_ids.in_use;
 406                 shm_get_stat (&shm_info.shm_rss, &shm_info.shm_swp);
 407                 shm_info.shm_tot = shm_tot;
 408                 shm_info.swap_attempts = 0;
 409                 shm_info.swap_successes = 0;
 410                 err = shm_ids.max_id;
 411                 shm_unlockall();
 412                 up(&shm_ids.sem);
 413                 if(copy_to_user (buf, &shm_info, sizeof(shm_info)))
 414                         return -EFAULT;
 415
 416                 return err < 0 ? 0 : err;
 417         }
 418         case SHM_STAT:
 419         case IPC_STAT:
 420         {
 421                 struct shmid64_ds tbuf;
 422                 int result;
 423                 memset(&tbuf, 0, sizeof(tbuf));
 424                 shp = shm_lock(shmid);
 425                 if(shp==NULL)
 426                         return -EINVAL;
 427                 if(cmd==SHM_STAT) {
 428                         err = -EINVAL;
 429                         if (shmid > shm_ids.max_id)
 430                                 goto out_unlock;
 431                         result = shm_buildid(shmid, shp->shm_perm.seq);
 432                 } else {
 433                         err = shm_checkid(shp,shmid);
 434                         if(err)
 435                                 goto out_unlock;
 436                         result = 0;
 437                 }
 438                 err=-EACCES;
 439                 if (ipcperms (&shp->shm_perm, S_IRUGO))
 440                         goto out_unlock;
 441                 kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);
 442                 tbuf.shm_segsz  = shp->shm_segsz;
 443                 tbuf.shm_atime  = shp->shm_atim;
 444                 tbuf.shm_dtime  = shp->shm_dtim;
 445                 tbuf.shm_ctime  = shp->shm_ctim;
 446                 tbuf.shm_cpid   = shp->shm_cprid;
 447                 tbuf.shm_lpid   = shp->shm_lprid;
 448                 tbuf.shm_nattch = shp->shm_nattch;
 449                 shm_unlock(shmid);
 450                 if(copy_shmid_to_user (buf, &tbuf, version))
 451                         return -EFAULT;
 452                 return result;
 453         }
 454         case SHM_LOCK:
 455         case SHM_UNLOCK:
 456         {
 457 /* Allow superuser to lock segment in memory */
 458 /* Should the pages be faulted in here or leave it to user? */
 459 /* need to determine interaction with current->swappable */
 460                 if (!capable(CAP_IPC_LOCK))
 461                         return -EPERM;
 462
 463                 shp = shm_lock(shmid);
 464                 if(shp==NULL)
 465                         return -EINVAL;
 466                 err = shm_checkid(shp,shmid);
 467                 if(err)
 468                         goto out_unlock;
 469                 if(cmd==SHM_LOCK) {
 470                         shp->shm_file->f_dentry->d_inode->u.shmem_i.locked = 1;
 471                         shp->shm_flags |= SHM_LOCKED;
 472                 } else {
 473                         shp->shm_file->f_dentry->d_inode->u.shmem_i.locked = 0;
 474                         shp->shm_flags &= ~SHM_LOCKED;
 475                 }
 476                 shm_unlock(shmid);
 477                 return err;
 478         }
 479         case IPC_RMID:
 480         {
 481                 /*
 482                  *      We cannot simply remove the file. The SVID states
 483                  *      that the block remains until the last person
 484                  *      detaches from it, then is deleted. A shmat() on
 485                  *      an RMID segment is legal in older Linux and if
 486                  *      we change it apps break...
 487                  *
 488                  *      Instead we set a destroyed flag, and then blow
 489                  *      the name away when the usage hits zero.
 490                  */
 491                 down(&shm_ids.sem);
 492                 shp = shm_lock(shmid);
 493                 err = -EINVAL;
 494                 if (shp == NULL)
 495                         goto out_up;
 496                 err = shm_checkid(shp, shmid);
 497                 if (err == 0) {
 498                         if (shp->shm_nattch){
 499                                 shp->shm_flags |= SHM_DEST;
 500                                 /* Do not find it any more */
 501                                 shp->shm_perm.key = IPC_PRIVATE;
 502                         } else
 503                                 shm_destroy (shp);
 504                 }
 505                 /* Unlock */
 506                 shm_unlock(shmid);
 507                 up(&shm_ids.sem);
 508                 return err;
 509         }
 510
 511         case IPC_SET:
 512         {
 513                 if(copy_shmid_from_user (&setbuf, buf, version))
 514                         return -EFAULT;
 515                 down(&shm_ids.sem);
 516                 shp = shm_lock(shmid);
 517                 err=-EINVAL;
 518                 if(shp==NULL)
 519                         goto out_up;
 520                 err = shm_checkid(shp,shmid);
 521                 if(err)
 522                         goto out_unlock_up;
 523                 err=-EPERM;
 524                 if (current->euid != shp->shm_perm.uid &&
 525                     current->euid != shp->shm_perm.cuid &&
 526                     !capable(CAP_SYS_ADMIN)) {
 527                         goto out_unlock_up;
 528                 }
 529
 530                 shp->shm_perm.uid = setbuf.uid;
 531                 shp->shm_perm.gid = setbuf.gid;
 532                 shp->shm_flags = (shp->shm_flags & ~S_IRWXUGO)
 533                         | (setbuf.mode & S_IRWXUGO);
 534                 shp->shm_ctim = CURRENT_TIME;
 535                 break;
 536         }
 537
 538         default:
 539                 return -EINVAL;
 540         }
 541
 542         err = 0;
 543 out_unlock_up:
 544         shm_unlock(shmid);
 545 out_up:
 546         up(&shm_ids.sem);
 547         return err;
 548 out_unlock:
 549         shm_unlock(shmid);
 550         return err;
 551 }
 552
 553 /*
 554  * Fix shmaddr, allocate descriptor, map shm, add attach descriptor to lists.
 555  */
 556 asmlinkage long sys_shmat (int shmid, char *shmaddr, int shmflg, ulong *raddr)
 557 {
 558         struct shmid_kernel *shp;
 559         unsigned long addr;
 560         struct file * file;
 561         int    err;
 562         unsigned long flags;
 563         unsigned long prot;
 564         unsigned long o_flags;
 565         int acc_mode;
 566         void *user_addr;
 567
 568         if (shmid < 0)
 569                 return -EINVAL;
 570
 571         if ((addr = (ulong)shmaddr)) {
 572                 if (addr & (SHMLBA-1)) {
 573                         if (shmflg & SHM_RND)
 574                                 addr &= ~(SHMLBA-1);       /* round down */
 575                         else
 576                                 return -EINVAL;
 577                 }
 578                 flags = MAP_SHARED | MAP_FIXED;
 579         } else
 580                 flags = MAP_SHARED;
 581
 582         if (shmflg & SHM_RDONLY) {
 583                 prot = PROT_READ;
 584                 o_flags = O_RDONLY;
 585                 acc_mode = S_IRUGO;
 586         } else {
 587                 prot = PROT_READ | PROT_WRITE;
 588                 o_flags = O_RDWR;
 589                 acc_mode = S_IRUGO | S_IWUGO;
 590         }
 591
 592         /*
 593          * We cannot rely on the fs check since SYSV IPC does have an
 594          * aditional creator id...
 595          */
 596         shp = shm_lock(shmid);
 597         if(shp == NULL)
 598                 return -EINVAL;
 599         if (ipcperms(&shp->shm_perm, acc_mode)) {
 600                 shm_unlock(shmid);
 601                 return -EACCES;
 602         }
 603         file = shp->shm_file;
 604         shp->shm_nattch++;
 605         shm_unlock(shmid);
 606
 607         down(&current->mm->mmap_sem);
 608         user_addr = (void *) do_mmap (file, addr, file->f_dentry->d_inode->i_size, prot, flags, 0);
 609         up(&current->mm->mmap_sem);
 610
 611         down (&shm_ids.sem);
 612         if(!(shp = shm_lock(shmid)))
 613                 BUG();
 614         shp->shm_nattch--;
 615         if(shp->shm_nattch == 0 &&
 616            shp->shm_flags & SHM_DEST)
 617                 shm_destroy (shp);
 618         shm_unlock(shmid);
 619         up (&shm_ids.sem);
 620
 621         *raddr = (unsigned long) user_addr;
 622         err = 0;
 623         if (IS_ERR(user_addr))
 624                 err = PTR_ERR(user_addr);
 625         return err;
 626
 627 }
 628
 629 /*
 630  * detach and kill segment if marked destroyed.
 631  * The work is done in shm_close.
 632  */
 633 asmlinkage long sys_shmdt (char *shmaddr)
 634 {
 635         struct mm_struct *mm = current->mm;
 636         struct vm_area_struct *shmd, *shmdnext;
 637
 638         down(&mm->mmap_sem);
 639         for (shmd = mm->mmap; shmd; shmd = shmdnext) {
 640                 shmdnext = shmd->vm_next;
 641                 if (shmd->vm_ops == &shm_vm_ops
 642                     && shmd->vm_start - (shmd->vm_pgoff << PAGE_SHIFT) == (ulong) shmaddr)
 643                         do_munmap(mm, shmd->vm_start, shmd->vm_end - shmd->vm_start);
 644         }
 645         up(&mm->mmap_sem);
 646         return 0;
 647 }
 648
 649 #ifdef CONFIG_PROC_FS
 650 static int sysvipc_shm_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
 651 {
 652         off_t pos = 0;
 653         off_t begin = 0;
 654         int i, len = 0;
 655
 656         down(&shm_ids.sem);
 657         len += sprintf(buffer, "       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime\n");
 658
 659         for(i = 0; i <= shm_ids.max_id; i++) {
 660                 struct shmid_kernel* shp;
 661
 662                 shp = shm_lock(i);
 663                 if(shp!=NULL) {
 664 #define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
 665 #define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
 666                         char *format;
 667
 668                         if (sizeof(size_t) <= sizeof(int))
 669                                 format = SMALL_STRING;
 670                         else
 671                                 format = BIG_STRING;
 672                         len += sprintf(buffer + len, format,
 673                                 shp->shm_perm.key,
 674                                 shm_buildid(i, shp->shm_perm.seq),
 675                                 shp->shm_flags,
 676                                 shp->shm_segsz,
 677                                 shp->shm_cprid,
 678                                 shp->shm_lprid,
 679                                 shp->shm_nattch,
 680                                 shp->shm_perm.uid,
 681                                 shp->shm_perm.gid,
 682                                 shp->shm_perm.cuid,
 683                                 shp->shm_perm.cgid,
 684                                 shp->shm_atim,
 685                                 shp->shm_dtim,
 686                                 shp->shm_ctim);
 687                         shm_unlock(i);
 688
 689                         pos += len;
 690                         if(pos < offset) {
 691                                 len = 0;
 692                                 begin = pos;
 693                         }
 694                         if(pos > offset + length)
 695                                 goto done;
 696                 }
 697         }
 698         *eof = 1;
 699 done:
 700         up(&shm_ids.sem);
 701         *start = buffer + (offset - begin);
 702         len -= (offset - begin);
 703         if(len > length)
 704                 len = length;
 705         if(len < 0)
 706                 len = 0;
 707         return len;
 708 }
 709 #endif