drivers/char/mem.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/drivers/char/mem.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *
   7  *  Added devfs support.
   8  *    Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
   9  *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
  10  */
  11
  12 #include <linux/mm.h>
  13 #include <linux/miscdevice.h>
  14 #include <linux/slab.h>
  15 #include <linux/vmalloc.h>
  16 #include <linux/mman.h>
  17 #include <linux/random.h>
  18 #include <linux/init.h>
  19 #include <linux/tty.h>
  20 #include <linux/capability.h>
  21 #include <linux/ptrace.h>
  22 #include <linux/device.h>
  23 #include <linux/highmem.h>
  24 #include <linux/backing-dev.h>
  25 #include <linux/shmem_fs.h>
  26 #include <linux/splice.h>
  27 #include <linux/pfn.h>
  28 #include <linux/export.h>
  29 #include <linux/io.h>
  30 #include <linux/uio.h>
  31 #include <linux/uaccess.h>
  32 #include <linux/security.h>
  33
  34 #ifdef CONFIG_IA64
  35 # include <linux/efi.h>
  36 #endif
  37
  38 #define DEVMEM_MINOR    1
  39 #define DEVPORT_MINOR   4
  40
  41 static inline unsigned long size_inside_page(unsigned long start,
  42                                              unsigned long size)
  43 {
  44         unsigned long sz;
  45
  46         sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));
  47
  48         return min(sz, size);
  49 }
  50
  51 #ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE
  52 static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
  53 {
  54         return addr + count <= __pa(high_memory);
  55 }
  56
  57 static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
  58 {
  59         return 1;
  60 }
  61 #endif
  62
  63 #ifdef CONFIG_STRICT_DEVMEM
  64 static inline int page_is_allowed(unsigned long pfn)
  65 {
  66         return devmem_is_allowed(pfn);
  67 }
  68 static inline int range_is_allowed(unsigned long pfn, unsigned long size)
  69 {
  70         u64 from = ((u64)pfn) << PAGE_SHIFT;
  71         u64 to = from + size;
  72         u64 cursor = from;
  73
  74         while (cursor < to) {
  75                 if (!devmem_is_allowed(pfn))
  76                         return 0;
  77                 cursor += PAGE_SIZE;
  78                 pfn++;
  79         }
  80         return 1;
  81 }
  82 #else
  83 static inline int page_is_allowed(unsigned long pfn)
  84 {
  85         return 1;
  86 }
  87 static inline int range_is_allowed(unsigned long pfn, unsigned long size)
  88 {
  89         return 1;
  90 }
  91 #endif
  92
  93 #ifndef unxlate_dev_mem_ptr
  94 #define unxlate_dev_mem_ptr unxlate_dev_mem_ptr
  95 void __weak unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
  96 {
  97 }
  98 #endif
  99
 100 static inline bool should_stop_iteration(void)
 101 {
 102         if (need_resched())
 103                 cond_resched();
 104         return fatal_signal_pending(current);
 105 }
 106
 107 /*
 108  * This funcion reads the *physical* memory. The f_pos points directly to the
 109  * memory location.
 110  */
 111 static ssize_t read_mem(struct file *file, char __user *buf,
 112                         size_t count, loff_t *ppos)
 113 {
 114         phys_addr_t p = *ppos;
 115         ssize_t read, sz;
 116         void *ptr;
 117         char *bounce;
 118         int err;
 119
 120         if (p != *ppos)
 121                 return 0;
 122
 123         if (!valid_phys_addr_range(p, count))
 124                 return -EFAULT;
 125         read = 0;
 126 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 127         /* we don't have page 0 mapped on sparc and m68k.. */
 128         if (p < PAGE_SIZE) {
 129                 sz = size_inside_page(p, count);
 130                 if (sz > 0) {
 131                         if (clear_user(buf, sz))
 132                                 return -EFAULT;
 133                         buf += sz;
 134                         p += sz;
 135                         count -= sz;
 136                         read += sz;
 137                 }
 138         }
 139 #endif
 140
 141         bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
 142         if (!bounce)
 143                 return -ENOMEM;
 144
 145         while (count > 0) {
 146                 unsigned long remaining;
 147                 int allowed, probe;
 148
 149                 sz = size_inside_page(p, count);
 150
 151                 err = -EPERM;
 152                 allowed = page_is_allowed(p >> PAGE_SHIFT);
 153                 if (!allowed)
 154                         goto failed;
 155
 156                 err = -EFAULT;
 157                 if (allowed == 2) {
 158                         /* Show zeros for restricted memory. */
 159                         remaining = clear_user(buf, sz);
 160                 } else {
 161                         /*
 162                          * On ia64 if a page has been mapped somewhere as
 163                          * uncached, then it must also be accessed uncached
 164                          * by the kernel or data corruption may occur.
 165                          */
 166                         ptr = xlate_dev_mem_ptr(p);
 167                         if (!ptr)
 168                                 goto failed;
 169
 170                         probe = copy_from_kernel_nofault(bounce, ptr, sz);
 171                         unxlate_dev_mem_ptr(p, ptr);
 172                         if (probe)
 173                                 goto failed;
 174
 175                         remaining = copy_to_user(buf, bounce, sz);
 176                 }
 177
 178                 if (remaining)
 179                         goto failed;
 180
 181                 buf += sz;
 182                 p += sz;
 183                 count -= sz;
 184                 read += sz;
 185                 if (should_stop_iteration())
 186                         break;
 187         }
 188         kfree(bounce);
 189
 190         *ppos += read;
 191         return read;
 192
 193 failed:
 194         kfree(bounce);
 195         return err;
 196 }
 197
 198 static ssize_t write_mem(struct file *file, const char __user *buf,
 199                          size_t count, loff_t *ppos)
 200 {
 201         phys_addr_t p = *ppos;
 202         ssize_t written, sz;
 203         unsigned long copied;
 204         void *ptr;
 205
 206         if (p != *ppos)
 207                 return -EFBIG;
 208
 209         if (!valid_phys_addr_range(p, count))
 210                 return -EFAULT;
 211
 212         written = 0;
 213
 214 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 215         /* we don't have page 0 mapped on sparc and m68k.. */
 216         if (p < PAGE_SIZE) {
 217                 sz = size_inside_page(p, count);
 218                 /* Hmm. Do something? */
 219                 buf += sz;
 220                 p += sz;
 221                 count -= sz;
 222                 written += sz;
 223         }
 224 #endif
 225
 226         while (count > 0) {
 227                 int allowed;
 228
 229                 sz = size_inside_page(p, count);
 230
 231                 allowed = page_is_allowed(p >> PAGE_SHIFT);
 232                 if (!allowed)
 233                         return -EPERM;
 234
 235                 /* Skip actual writing when a page is marked as restricted. */
 236                 if (allowed == 1) {
 237                         /*
 238                          * On ia64 if a page has been mapped somewhere as
 239                          * uncached, then it must also be accessed uncached
 240                          * by the kernel or data corruption may occur.
 241                          */
 242                         ptr = xlate_dev_mem_ptr(p);
 243                         if (!ptr) {
 244                                 if (written)
 245                                         break;
 246                                 return -EFAULT;
 247                         }
 248
 249                         copied = copy_from_user(ptr, buf, sz);
 250                         unxlate_dev_mem_ptr(p, ptr);
 251                         if (copied) {
 252                                 written += sz - copied;
 253                                 if (written)
 254                                         break;
 255                                 return -EFAULT;
 256                         }
 257                 }
 258
 259                 buf += sz;
 260                 p += sz;
 261                 count -= sz;
 262                 written += sz;
 263                 if (should_stop_iteration())
 264                         break;
 265         }
 266
 267         *ppos += written;
 268         return written;
 269 }
 270
 271 int __weak phys_mem_access_prot_allowed(struct file *file,
 272         unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
 273 {
 274         return 1;
 275 }
 276
 277 #ifndef __HAVE_PHYS_MEM_ACCESS_PROT
 278
 279 /*
 280  * Architectures vary in how they handle caching for addresses
 281  * outside of main memory.
 282  *
 283  */
 284 #ifdef pgprot_noncached
 285 static int uncached_access(struct file *file, phys_addr_t addr)
 286 {
 287 #if defined(CONFIG_IA64)
 288         /*
 289          * On ia64, we ignore O_DSYNC because we cannot tolerate memory
 290          * attribute aliases.
 291          */
 292         return !(efi_mem_attributes(addr) & EFI_MEMORY_WB);
 293 #else
 294         /*
 295          * Accessing memory above the top the kernel knows about or through a
 296          * file pointer
 297          * that was marked O_DSYNC will be done non-cached.
 298          */
 299         if (file->f_flags & O_DSYNC)
 300                 return 1;
 301         return addr >= __pa(high_memory);
 302 #endif
 303 }
 304 #endif
 305
 306 static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 307                                      unsigned long size, pgprot_t vma_prot)
 308 {
 309 #ifdef pgprot_noncached
 310         phys_addr_t offset = pfn << PAGE_SHIFT;
 311
 312         if (uncached_access(file, offset))
 313                 return pgprot_noncached(vma_prot);
 314 #endif
 315         return vma_prot;
 316 }
 317 #endif
 318
 319 #ifndef CONFIG_MMU
 320 static unsigned long get_unmapped_area_mem(struct file *file,
 321                                            unsigned long addr,
 322                                            unsigned long len,
 323                                            unsigned long pgoff,
 324                                            unsigned long flags)
 325 {
 326         if (!valid_mmap_phys_addr_range(pgoff, len))
 327                 return (unsigned long) -EINVAL;
 328         return pgoff << PAGE_SHIFT;
 329 }
 330
 331 /* permit direct mmap, for read, write or exec */
 332 static unsigned memory_mmap_capabilities(struct file *file)
 333 {
 334         return NOMMU_MAP_DIRECT |
 335                 NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
 336 }
 337
 338 static unsigned zero_mmap_capabilities(struct file *file)
 339 {
 340         return NOMMU_MAP_COPY;
 341 }
 342
 343 /* can't do an in-place private mapping if there's no MMU */
 344 static inline int private_mapping_ok(struct vm_area_struct *vma)
 345 {
 346         return vma->vm_flags & VM_MAYSHARE;
 347 }
 348 #else
 349
 350 static inline int private_mapping_ok(struct vm_area_struct *vma)
 351 {
 352         return 1;
 353 }
 354 #endif
 355
 356 static const struct vm_operations_struct mmap_mem_ops = {
 357 #ifdef CONFIG_HAVE_IOREMAP_PROT
 358         .access = generic_access_phys
 359 #endif
 360 };
 361
 362 static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 363 {
 364         size_t size = vma->vm_end - vma->vm_start;
 365         phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
 366
 367         /* Does it even fit in phys_addr_t? */
 368         if (offset >> PAGE_SHIFT != vma->vm_pgoff)
 369                 return -EINVAL;
 370
 371         /* It's illegal to wrap around the end of the physical address space. */
 372         if (offset + (phys_addr_t)size - 1 < offset)
 373                 return -EINVAL;
 374
 375         if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
 376                 return -EINVAL;
 377
 378         if (!private_mapping_ok(vma))
 379                 return -ENOSYS;
 380
 381         if (!range_is_allowed(vma->vm_pgoff, size))
 382                 return -EPERM;
 383
 384         if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
 385                                                 &vma->vm_page_prot))
 386                 return -EINVAL;
 387
 388         vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
 389                                                  size,
 390                                                  vma->vm_page_prot);
 391
 392         vma->vm_ops = &mmap_mem_ops;
 393
 394         /* Remap-pfn-range will mark the range VM_IO */
 395         if (remap_pfn_range(vma,
 396                             vma->vm_start,
 397                             vma->vm_pgoff,
 398                             size,
 399                             vma->vm_page_prot)) {
 400                 return -EAGAIN;
 401         }
 402         return 0;
 403 }
 404
 405 static ssize_t read_port(struct file *file, char __user *buf,
 406                          size_t count, loff_t *ppos)
 407 {
 408         unsigned long i = *ppos;
 409         char __user *tmp = buf;
 410
 411         if (!access_ok(buf, count))
 412                 return -EFAULT;
 413         while (count-- > 0 && i < 65536) {
 414                 if (__put_user(inb(i), tmp) < 0)
 415                         return -EFAULT;
 416                 i++;
 417                 tmp++;
 418         }
 419         *ppos = i;
 420         return tmp-buf;
 421 }
 422
 423 static ssize_t write_port(struct file *file, const char __user *buf,
 424                           size_t count, loff_t *ppos)
 425 {
 426         unsigned long i = *ppos;
 427         const char __user *tmp = buf;
 428
 429         if (!access_ok(buf, count))
 430                 return -EFAULT;
 431         while (count-- > 0 && i < 65536) {
 432                 char c;
 433
 434                 if (__get_user(c, tmp)) {
 435                         if (tmp > buf)
 436                                 break;
 437                         return -EFAULT;
 438                 }
 439                 outb(c, i);
 440                 i++;
 441                 tmp++;
 442         }
 443         *ppos = i;
 444         return tmp-buf;
 445 }
 446
 447 static ssize_t read_null(struct file *file, char __user *buf,
 448                          size_t count, loff_t *ppos)
 449 {
 450         return 0;
 451 }
 452
 453 static ssize_t write_null(struct file *file, const char __user *buf,
 454                           size_t count, loff_t *ppos)
 455 {
 456         return count;
 457 }
 458
 459 static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
 460 {
 461         return 0;
 462 }
 463
 464 static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
 465 {
 466         size_t count = iov_iter_count(from);
 467         iov_iter_advance(from, count);
 468         return count;
 469 }
 470
 471 static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
 472                         struct splice_desc *sd)
 473 {
 474         return sd->len;
 475 }
 476
 477 static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
 478                                  loff_t *ppos, size_t len, unsigned int flags)
 479 {
 480         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
 481 }
 482
 483 static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
 484 {
 485         size_t written = 0;
 486
 487         while (iov_iter_count(iter)) {
 488                 size_t chunk = iov_iter_count(iter), n;
 489
 490                 if (chunk > PAGE_SIZE)
 491                         chunk = PAGE_SIZE;      /* Just for latency reasons */
 492                 n = iov_iter_zero(chunk, iter);
 493                 if (!n && iov_iter_count(iter))
 494                         return written ? written : -EFAULT;
 495                 written += n;
 496                 if (signal_pending(current))
 497                         return written ? written : -ERESTARTSYS;
 498                 cond_resched();
 499         }
 500         return written;
 501 }
 502
 503 static ssize_t read_zero(struct file *file, char __user *buf,
 504                          size_t count, loff_t *ppos)
 505 {
 506         size_t cleared = 0;
 507
 508         while (count) {
 509                 size_t chunk = min_t(size_t, count, PAGE_SIZE);
 510                 size_t left;
 511
 512                 left = clear_user(buf + cleared, chunk);
 513                 if (unlikely(left)) {
 514                         cleared += (chunk - left);
 515                         if (!cleared)
 516                                 return -EFAULT;
 517                         break;
 518                 }
 519                 cleared += chunk;
 520                 count -= chunk;
 521
 522                 if (signal_pending(current))
 523                         break;
 524                 cond_resched();
 525         }
 526
 527         return cleared;
 528 }
 529
 530 static int mmap_zero(struct file *file, struct vm_area_struct *vma)
 531 {
 532 #ifndef CONFIG_MMU
 533         return -ENOSYS;
 534 #endif
 535         if (vma->vm_flags & VM_SHARED)
 536                 return shmem_zero_setup(vma);
 537         vma_set_anonymous(vma);
 538         return 0;
 539 }
 540
 541 static unsigned long get_unmapped_area_zero(struct file *file,
 542                                 unsigned long addr, unsigned long len,
 543                                 unsigned long pgoff, unsigned long flags)
 544 {
 545 #ifdef CONFIG_MMU
 546         if (flags & MAP_SHARED) {
 547                 /*
 548                  * mmap_zero() will call shmem_zero_setup() to create a file,
 549                  * so use shmem's get_unmapped_area in case it can be huge;
 550                  * and pass NULL for file as in mmap.c's get_unmapped_area(),
 551                  * so as not to confuse shmem with our handle on "/dev/zero".
 552                  */
 553                 return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
 554         }
 555
 556         /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
 557         return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
 558 #else
 559         return -ENOSYS;
 560 #endif
 561 }
 562
 563 static ssize_t write_full(struct file *file, const char __user *buf,
 564                           size_t count, loff_t *ppos)
 565 {
 566         return -ENOSPC;
 567 }
 568
 569 /*
 570  * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
 571  * can fopen() both devices with "a" now.  This was previously impossible.
 572  * -- SRB.
 573  */
 574 static loff_t null_lseek(struct file *file, loff_t offset, int orig)
 575 {
 576         return file->f_pos = 0;
 577 }
 578
 579 /*
 580  * The memory devices use the full 32/64 bits of the offset, and so we cannot
 581  * check against negative addresses: they are ok. The return value is weird,
 582  * though, in that case (0).
 583  *
 584  * also note that seeking relative to the "end of file" isn't supported:
 585  * it has no meaning, so it returns -EINVAL.
 586  */
 587 static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 588 {
 589         loff_t ret;
 590
 591         inode_lock(file_inode(file));
 592         switch (orig) {
 593         case SEEK_CUR:
 594                 offset += file->f_pos;
 595                 fallthrough;
 596         case SEEK_SET:
 597                 /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
 598                 if ((unsigned long long)offset >= -MAX_ERRNO) {
 599                         ret = -EOVERFLOW;
 600                         break;
 601                 }
 602                 file->f_pos = offset;
 603                 ret = file->f_pos;
 604                 force_successful_syscall_return();
 605                 break;
 606         default:
 607                 ret = -EINVAL;
 608         }
 609         inode_unlock(file_inode(file));
 610         return ret;
 611 }
 612
 613 static int open_port(struct inode *inode, struct file *filp)
 614 {
 615         int rc;
 616
 617         if (!capable(CAP_SYS_RAWIO))
 618                 return -EPERM;
 619
 620         rc = security_locked_down(LOCKDOWN_DEV_MEM);
 621         if (rc)
 622                 return rc;
 623
 624         if (iminor(inode) != DEVMEM_MINOR)
 625                 return 0;
 626
 627         /*
 628          * Use a unified address space to have a single point to manage
 629          * revocations when drivers want to take over a /dev/mem mapped
 630          * range.
 631          */
 632         filp->f_mapping = iomem_get_mapping();
 633
 634         return 0;
 635 }
 636
 637 #define zero_lseek      null_lseek
 638 #define full_lseek      null_lseek
 639 #define write_zero      write_null
 640 #define write_iter_zero write_iter_null
 641 #define open_mem        open_port
 642
 643 static const struct file_operations __maybe_unused mem_fops = {
 644         .llseek         = memory_lseek,
 645         .read           = read_mem,
 646         .write          = write_mem,
 647         .mmap           = mmap_mem,
 648         .open           = open_mem,
 649 #ifndef CONFIG_MMU
 650         .get_unmapped_area = get_unmapped_area_mem,
 651         .mmap_capabilities = memory_mmap_capabilities,
 652 #endif
 653 };
 654
 655 static const struct file_operations null_fops = {
 656         .llseek         = null_lseek,
 657         .read           = read_null,
 658         .write          = write_null,
 659         .read_iter      = read_iter_null,
 660         .write_iter     = write_iter_null,
 661         .splice_write   = splice_write_null,
 662 };
 663
 664 static const struct file_operations __maybe_unused port_fops = {
 665         .llseek         = memory_lseek,
 666         .read           = read_port,
 667         .write          = write_port,
 668         .open           = open_port,
 669 };
 670
 671 static const struct file_operations zero_fops = {
 672         .llseek         = zero_lseek,
 673         .write          = write_zero,
 674         .read_iter      = read_iter_zero,
 675         .read           = read_zero,
 676         .write_iter     = write_iter_zero,
 677         .mmap           = mmap_zero,
 678         .get_unmapped_area = get_unmapped_area_zero,
 679 #ifndef CONFIG_MMU
 680         .mmap_capabilities = zero_mmap_capabilities,
 681 #endif
 682 };
 683
 684 static const struct file_operations full_fops = {
 685         .llseek         = full_lseek,
 686         .read_iter      = read_iter_zero,
 687         .write          = write_full,
 688 };
 689
 690 static const struct memdev {
 691         const char *name;
 692         umode_t mode;
 693         const struct file_operations *fops;
 694         fmode_t fmode;
 695 } devlist[] = {
 696 #ifdef CONFIG_DEVMEM
 697          [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
 698 #endif
 699          [3] = { "null", 0666, &null_fops, 0 },
 700 #ifdef CONFIG_DEVPORT
 701          [4] = { "port", 0, &port_fops, 0 },
 702 #endif
 703          [5] = { "zero", 0666, &zero_fops, 0 },
 704          [7] = { "full", 0666, &full_fops, 0 },
 705          [8] = { "random", 0666, &random_fops, 0 },
 706          [9] = { "urandom", 0666, &urandom_fops, 0 },
 707 #ifdef CONFIG_PRINTK
 708         [11] = { "kmsg", 0644, &kmsg_fops, 0 },
 709 #endif
 710 };
 711
 712 static int memory_open(struct inode *inode, struct file *filp)
 713 {
 714         int minor;
 715         const struct memdev *dev;
 716
 717         minor = iminor(inode);
 718         if (minor >= ARRAY_SIZE(devlist))
 719                 return -ENXIO;
 720
 721         dev = &devlist[minor];
 722         if (!dev->fops)
 723                 return -ENXIO;
 724
 725         filp->f_op = dev->fops;
 726         filp->f_mode |= dev->fmode;
 727
 728         if (dev->fops->open)
 729                 return dev->fops->open(inode, filp);
 730
 731         return 0;
 732 }
 733
 734 static const struct file_operations memory_fops = {
 735         .open = memory_open,
 736         .llseek = noop_llseek,
 737 };
 738
 739 static char *mem_devnode(struct device *dev, umode_t *mode)
 740 {
 741         if (mode && devlist[MINOR(dev->devt)].mode)
 742                 *mode = devlist[MINOR(dev->devt)].mode;
 743         return NULL;
 744 }
 745
 746 static struct class *mem_class;
 747
 748 static int __init chr_dev_init(void)
 749 {
 750         int minor;
 751
 752         if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
 753                 printk("unable to get major %d for memory devs\n", MEM_MAJOR);
 754
 755         mem_class = class_create(THIS_MODULE, "mem");
 756         if (IS_ERR(mem_class))
 757                 return PTR_ERR(mem_class);
 758
 759         mem_class->devnode = mem_devnode;
 760         for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
 761                 if (!devlist[minor].name)
 762                         continue;
 763
 764                 /*
 765                  * Create /dev/port?
 766                  */
 767                 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
 768                         continue;
 769
 770                 device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
 771                               NULL, devlist[minor].name);
 772         }
 773
 774         return tty_init();
 775 }
 776
 777 fs_initcall(chr_dev_init);