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