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 static inline bool should_stop_iteration(void)
  94 {
  95         if (need_resched())
  96                 cond_resched();
  97         return signal_pending(current);
  98 }
  99
 100 /*
 101  * This funcion reads the *physical* memory. The f_pos points directly to the
 102  * memory location.
 103  */
 104 static ssize_t read_mem(struct file *file, char __user *buf,
 105                         size_t count, loff_t *ppos)
 106 {
 107         phys_addr_t p = *ppos;
 108         ssize_t read, sz;
 109         void *ptr;
 110         char *bounce;
 111         int err;
 112
 113         if (p != *ppos)
 114                 return 0;
 115
 116         if (!valid_phys_addr_range(p, count))
 117                 return -EFAULT;
 118         read = 0;
 119 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 120         /* we don't have page 0 mapped on sparc and m68k.. */
 121         if (p < PAGE_SIZE) {
 122                 sz = size_inside_page(p, count);
 123                 if (sz > 0) {
 124                         if (clear_user(buf, sz))
 125                                 return -EFAULT;
 126                         buf += sz;
 127                         p += sz;
 128                         count -= sz;
 129                         read += sz;
 130                 }
 131         }
 132 #endif
 133
 134         bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
 135         if (!bounce)
 136                 return -ENOMEM;
 137
 138         while (count > 0) {
 139                 unsigned long remaining;
 140                 int allowed, probe;
 141
 142                 sz = size_inside_page(p, count);
 143
 144                 err = -EPERM;
 145                 allowed = page_is_allowed(p >> PAGE_SHIFT);
 146                 if (!allowed)
 147                         goto failed;
 148
 149                 err = -EFAULT;
 150                 if (allowed == 2) {
 151                         /* Show zeros for restricted memory. */
 152                         remaining = clear_user(buf, sz);
 153                 } else {
 154                         /*
 155                          * On ia64 if a page has been mapped somewhere as
 156                          * uncached, then it must also be accessed uncached
 157                          * by the kernel or data corruption may occur.
 158                          */
 159                         ptr = xlate_dev_mem_ptr(p);
 160                         if (!ptr)
 161                                 goto failed;
 162
 163                         probe = copy_from_kernel_nofault(bounce, ptr, sz);
 164                         unxlate_dev_mem_ptr(p, ptr);
 165                         if (probe)
 166                                 goto failed;
 167
 168                         remaining = copy_to_user(buf, bounce, sz);
 169                 }
 170
 171                 if (remaining)
 172                         goto failed;
 173
 174                 buf += sz;
 175                 p += sz;
 176                 count -= sz;
 177                 read += sz;
 178                 if (should_stop_iteration())
 179                         break;
 180         }
 181         kfree(bounce);
 182
 183         *ppos += read;
 184         return read;
 185
 186 failed:
 187         kfree(bounce);
 188         return err;
 189 }
 190
 191 static ssize_t write_mem(struct file *file, const char __user *buf,
 192                          size_t count, loff_t *ppos)
 193 {
 194         phys_addr_t p = *ppos;
 195         ssize_t written, sz;
 196         unsigned long copied;
 197         void *ptr;
 198
 199         if (p != *ppos)
 200                 return -EFBIG;
 201
 202         if (!valid_phys_addr_range(p, count))
 203                 return -EFAULT;
 204
 205         written = 0;
 206
 207 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 208         /* we don't have page 0 mapped on sparc and m68k.. */
 209         if (p < PAGE_SIZE) {
 210                 sz = size_inside_page(p, count);
 211                 /* Hmm. Do something? */
 212                 buf += sz;
 213                 p += sz;
 214                 count -= sz;
 215                 written += sz;
 216         }
 217 #endif
 218
 219         while (count > 0) {
 220                 int allowed;
 221
 222                 sz = size_inside_page(p, count);
 223
 224                 allowed = page_is_allowed(p >> PAGE_SHIFT);
 225                 if (!allowed)
 226                         return -EPERM;
 227
 228                 /* Skip actual writing when a page is marked as restricted. */
 229                 if (allowed == 1) {
 230                         /*
 231                          * On ia64 if a page has been mapped somewhere as
 232                          * uncached, then it must also be accessed uncached
 233                          * by the kernel or data corruption may occur.
 234                          */
 235                         ptr = xlate_dev_mem_ptr(p);
 236                         if (!ptr) {
 237                                 if (written)
 238                                         break;
 239                                 return -EFAULT;
 240                         }
 241
 242                         copied = copy_from_user(ptr, buf, sz);
 243                         unxlate_dev_mem_ptr(p, ptr);
 244                         if (copied) {
 245                                 written += sz - copied;
 246                                 if (written)
 247                                         break;
 248                                 return -EFAULT;
 249                         }
 250                 }
 251
 252                 buf += sz;
 253                 p += sz;
 254                 count -= sz;
 255                 written += sz;
 256                 if (should_stop_iteration())
 257                         break;
 258         }
 259
 260         *ppos += written;
 261         return written;
 262 }
 263
 264 int __weak phys_mem_access_prot_allowed(struct file *file,
 265         unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
 266 {
 267         return 1;
 268 }
 269
 270 #ifndef __HAVE_PHYS_MEM_ACCESS_PROT
 271
 272 /*
 273  * Architectures vary in how they handle caching for addresses
 274  * outside of main memory.
 275  *
 276  */
 277 #ifdef pgprot_noncached
 278 static int uncached_access(struct file *file, phys_addr_t addr)
 279 {
 280 #if defined(CONFIG_IA64)
 281         /*
 282          * On ia64, we ignore O_DSYNC because we cannot tolerate memory
 283          * attribute aliases.
 284          */
 285         return !(efi_mem_attributes(addr) & EFI_MEMORY_WB);
 286 #else
 287         /*
 288          * Accessing memory above the top the kernel knows about or through a
 289          * file pointer
 290          * that was marked O_DSYNC will be done non-cached.
 291          */
 292         if (file->f_flags & O_DSYNC)
 293                 return 1;
 294         return addr >= __pa(high_memory);
 295 #endif
 296 }
 297 #endif
 298
 299 static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 300                                      unsigned long size, pgprot_t vma_prot)
 301 {
 302 #ifdef pgprot_noncached
 303         phys_addr_t offset = pfn << PAGE_SHIFT;
 304
 305         if (uncached_access(file, offset))
 306                 return pgprot_noncached(vma_prot);
 307 #endif
 308         return vma_prot;
 309 }
 310 #endif
 311
 312 #ifndef CONFIG_MMU
 313 static unsigned long get_unmapped_area_mem(struct file *file,
 314                                            unsigned long addr,
 315                                            unsigned long len,
 316                                            unsigned long pgoff,
 317                                            unsigned long flags)
 318 {
 319         if (!valid_mmap_phys_addr_range(pgoff, len))
 320                 return (unsigned long) -EINVAL;
 321         return pgoff << PAGE_SHIFT;
 322 }
 323
 324 /* permit direct mmap, for read, write or exec */
 325 static unsigned memory_mmap_capabilities(struct file *file)
 326 {
 327         return NOMMU_MAP_DIRECT |
 328                 NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
 329 }
 330
 331 static unsigned zero_mmap_capabilities(struct file *file)
 332 {
 333         return NOMMU_MAP_COPY;
 334 }
 335
 336 /* can't do an in-place private mapping if there's no MMU */
 337 static inline int private_mapping_ok(struct vm_area_struct *vma)
 338 {
 339         return is_nommu_shared_mapping(vma->vm_flags);
 340 }
 341 #else
 342
 343 static inline int private_mapping_ok(struct vm_area_struct *vma)
 344 {
 345         return 1;
 346 }
 347 #endif
 348
 349 static const struct vm_operations_struct mmap_mem_ops = {
 350 #ifdef CONFIG_HAVE_IOREMAP_PROT
 351         .access = generic_access_phys
 352 #endif
 353 };
 354
 355 static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 356 {
 357         size_t size = vma->vm_end - vma->vm_start;
 358         phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
 359
 360         /* Does it even fit in phys_addr_t? */
 361         if (offset >> PAGE_SHIFT != vma->vm_pgoff)
 362                 return -EINVAL;
 363
 364         /* It's illegal to wrap around the end of the physical address space. */
 365         if (offset + (phys_addr_t)size - 1 < offset)
 366                 return -EINVAL;
 367
 368         if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
 369                 return -EINVAL;
 370
 371         if (!private_mapping_ok(vma))
 372                 return -ENOSYS;
 373
 374         if (!range_is_allowed(vma->vm_pgoff, size))
 375                 return -EPERM;
 376
 377         if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
 378                                                 &vma->vm_page_prot))
 379                 return -EINVAL;
 380
 381         vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
 382                                                  size,
 383                                                  vma->vm_page_prot);
 384
 385         vma->vm_ops = &mmap_mem_ops;
 386
 387         /* Remap-pfn-range will mark the range VM_IO */
 388         if (remap_pfn_range(vma,
 389                             vma->vm_start,
 390                             vma->vm_pgoff,
 391                             size,
 392                             vma->vm_page_prot)) {
 393                 return -EAGAIN;
 394         }
 395         return 0;
 396 }
 397
 398 static ssize_t read_port(struct file *file, char __user *buf,
 399                          size_t count, loff_t *ppos)
 400 {
 401         unsigned long i = *ppos;
 402         char __user *tmp = buf;
 403
 404         if (!access_ok(buf, count))
 405                 return -EFAULT;
 406         while (count-- > 0 && i < 65536) {
 407                 if (__put_user(inb(i), tmp) < 0)
 408                         return -EFAULT;
 409                 i++;
 410                 tmp++;
 411         }
 412         *ppos = i;
 413         return tmp-buf;
 414 }
 415
 416 static ssize_t write_port(struct file *file, const char __user *buf,
 417                           size_t count, loff_t *ppos)
 418 {
 419         unsigned long i = *ppos;
 420         const char __user *tmp = buf;
 421
 422         if (!access_ok(buf, count))
 423                 return -EFAULT;
 424         while (count-- > 0 && i < 65536) {
 425                 char c;
 426
 427                 if (__get_user(c, tmp)) {
 428                         if (tmp > buf)
 429                                 break;
 430                         return -EFAULT;
 431                 }
 432                 outb(c, i);
 433                 i++;
 434                 tmp++;
 435         }
 436         *ppos = i;
 437         return tmp-buf;
 438 }
 439
 440 static ssize_t read_null(struct file *file, char __user *buf,
 441                          size_t count, loff_t *ppos)
 442 {
 443         return 0;
 444 }
 445
 446 static ssize_t write_null(struct file *file, const char __user *buf,
 447                           size_t count, loff_t *ppos)
 448 {
 449         return count;
 450 }
 451
 452 static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
 453 {
 454         return 0;
 455 }
 456
 457 static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
 458 {
 459         size_t count = iov_iter_count(from);
 460         iov_iter_advance(from, count);
 461         return count;
 462 }
 463
 464 static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
 465                         struct splice_desc *sd)
 466 {
 467         return sd->len;
 468 }
 469
 470 static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
 471                                  loff_t *ppos, size_t len, unsigned int flags)
 472 {
 473         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
 474 }
 475
 476 static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
 477 {
 478         return 0;
 479 }
 480
 481 static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
 482 {
 483         size_t written = 0;
 484
 485         while (iov_iter_count(iter)) {
 486                 size_t chunk = iov_iter_count(iter), n;
 487
 488                 if (chunk > PAGE_SIZE)
 489                         chunk = PAGE_SIZE;      /* Just for latency reasons */
 490                 n = iov_iter_zero(chunk, iter);
 491                 if (!n && iov_iter_count(iter))
 492                         return written ? written : -EFAULT;
 493                 written += n;
 494                 if (signal_pending(current))
 495                         return written ? written : -ERESTARTSYS;
 496                 if (!need_resched())
 497                         continue;
 498                 if (iocb->ki_flags & IOCB_NOWAIT)
 499                         return written ? written : -EAGAIN;
 500                 cond_resched();
 501         }
 502         return written;
 503 }
 504
 505 static ssize_t read_zero(struct file *file, char __user *buf,
 506                          size_t count, loff_t *ppos)
 507 {
 508         size_t cleared = 0;
 509
 510         while (count) {
 511                 size_t chunk = min_t(size_t, count, PAGE_SIZE);
 512                 size_t left;
 513
 514                 left = clear_user(buf + cleared, chunk);
 515                 if (unlikely(left)) {
 516                         cleared += (chunk - left);
 517                         if (!cleared)
 518                                 return -EFAULT;
 519                         break;
 520                 }
 521                 cleared += chunk;
 522                 count -= chunk;
 523
 524                 if (signal_pending(current))
 525                         break;
 526                 cond_resched();
 527         }
 528
 529         return cleared;
 530 }
 531
 532 static int mmap_zero(struct file *file, struct vm_area_struct *vma)
 533 {
 534 #ifndef CONFIG_MMU
 535         return -ENOSYS;
 536 #endif
 537         if (vma->vm_flags & VM_SHARED)
 538                 return shmem_zero_setup(vma);
 539         vma_set_anonymous(vma);
 540         return 0;
 541 }
 542
 543 static unsigned long get_unmapped_area_zero(struct file *file,
 544                                 unsigned long addr, unsigned long len,
 545                                 unsigned long pgoff, unsigned long flags)
 546 {
 547 #ifdef CONFIG_MMU
 548         if (flags & MAP_SHARED) {
 549                 /*
 550                  * mmap_zero() will call shmem_zero_setup() to create a file,
 551                  * so use shmem's get_unmapped_area in case it can be huge;
 552                  * and pass NULL for file as in mmap.c's get_unmapped_area(),
 553                  * so as not to confuse shmem with our handle on "/dev/zero".
 554                  */
 555                 return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
 556         }
 557
 558         /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
 559         return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
 560 #else
 561         return -ENOSYS;
 562 #endif
 563 }
 564
 565 static ssize_t write_full(struct file *file, const char __user *buf,
 566                           size_t count, loff_t *ppos)
 567 {
 568         return -ENOSPC;
 569 }
 570
 571 /*
 572  * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
 573  * can fopen() both devices with "a" now.  This was previously impossible.
 574  * -- SRB.
 575  */
 576 static loff_t null_lseek(struct file *file, loff_t offset, int orig)
 577 {
 578         return file->f_pos = 0;
 579 }
 580
 581 /*
 582  * The memory devices use the full 32/64 bits of the offset, and so we cannot
 583  * check against negative addresses: they are ok. The return value is weird,
 584  * though, in that case (0).
 585  *
 586  * also note that seeking relative to the "end of file" isn't supported:
 587  * it has no meaning, so it returns -EINVAL.
 588  */
 589 static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 590 {
 591         loff_t ret;
 592
 593         inode_lock(file_inode(file));
 594         switch (orig) {
 595         case SEEK_CUR:
 596                 offset += file->f_pos;
 597                 fallthrough;
 598         case SEEK_SET:
 599                 /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
 600                 if ((unsigned long long)offset >= -MAX_ERRNO) {
 601                         ret = -EOVERFLOW;
 602                         break;
 603                 }
 604                 file->f_pos = offset;
 605                 ret = file->f_pos;
 606                 force_successful_syscall_return();
 607                 break;
 608         default:
 609                 ret = -EINVAL;
 610         }
 611         inode_unlock(file_inode(file));
 612         return ret;
 613 }
 614
 615 static int open_port(struct inode *inode, struct file *filp)
 616 {
 617         int rc;
 618
 619         if (!capable(CAP_SYS_RAWIO))
 620                 return -EPERM;
 621
 622         rc = security_locked_down(LOCKDOWN_DEV_MEM);
 623         if (rc)
 624                 return rc;
 625
 626         if (iminor(inode) != DEVMEM_MINOR)
 627                 return 0;
 628
 629         /*
 630          * Use a unified address space to have a single point to manage
 631          * revocations when drivers want to take over a /dev/mem mapped
 632          * range.
 633          */
 634         filp->f_mapping = iomem_get_mapping();
 635
 636         return 0;
 637 }
 638
 639 #define zero_lseek      null_lseek
 640 #define full_lseek      null_lseek
 641 #define write_zero      write_null
 642 #define write_iter_zero write_iter_null
 643 #define open_mem        open_port
 644
 645 static const struct file_operations __maybe_unused mem_fops = {
 646         .llseek         = memory_lseek,
 647         .read           = read_mem,
 648         .write          = write_mem,
 649         .mmap           = mmap_mem,
 650         .open           = open_mem,
 651 #ifndef CONFIG_MMU
 652         .get_unmapped_area = get_unmapped_area_mem,
 653         .mmap_capabilities = memory_mmap_capabilities,
 654 #endif
 655 };
 656
 657 static const struct file_operations null_fops = {
 658         .llseek         = null_lseek,
 659         .read           = read_null,
 660         .write          = write_null,
 661         .read_iter      = read_iter_null,
 662         .write_iter     = write_iter_null,
 663         .splice_write   = splice_write_null,
 664         .uring_cmd      = uring_cmd_null,
 665 };
 666
 667 static const struct file_operations __maybe_unused port_fops = {
 668         .llseek         = memory_lseek,
 669         .read           = read_port,
 670         .write          = write_port,
 671         .open           = open_port,
 672 };
 673
 674 static const struct file_operations zero_fops = {
 675         .llseek         = zero_lseek,
 676         .write          = write_zero,
 677         .read_iter      = read_iter_zero,
 678         .read           = read_zero,
 679         .write_iter     = write_iter_zero,
 680         .mmap           = mmap_zero,
 681         .get_unmapped_area = get_unmapped_area_zero,
 682 #ifndef CONFIG_MMU
 683         .mmap_capabilities = zero_mmap_capabilities,
 684 #endif
 685 };
 686
 687 static const struct file_operations full_fops = {
 688         .llseek         = full_lseek,
 689         .read_iter      = read_iter_zero,
 690         .write          = write_full,
 691 };
 692
 693 static const struct memdev {
 694         const char *name;
 695         umode_t mode;
 696         const struct file_operations *fops;
 697         fmode_t fmode;
 698 } devlist[] = {
 699 #ifdef CONFIG_DEVMEM
 700          [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
 701 #endif
 702          [3] = { "null", 0666, &null_fops, FMODE_NOWAIT },
 703 #ifdef CONFIG_DEVPORT
 704          [4] = { "port", 0, &port_fops, 0 },
 705 #endif
 706          [5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
 707          [7] = { "full", 0666, &full_fops, 0 },
 708          [8] = { "random", 0666, &random_fops, FMODE_NOWAIT },
 709          [9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },
 710 #ifdef CONFIG_PRINTK
 711         [11] = { "kmsg", 0644, &kmsg_fops, 0 },
 712 #endif
 713 };
 714
 715 static int memory_open(struct inode *inode, struct file *filp)
 716 {
 717         int minor;
 718         const struct memdev *dev;
 719
 720         minor = iminor(inode);
 721         if (minor >= ARRAY_SIZE(devlist))
 722                 return -ENXIO;
 723
 724         dev = &devlist[minor];
 725         if (!dev->fops)
 726                 return -ENXIO;
 727
 728         filp->f_op = dev->fops;
 729         filp->f_mode |= dev->fmode;
 730
 731         if (dev->fops->open)
 732                 return dev->fops->open(inode, filp);
 733
 734         return 0;
 735 }
 736
 737 static const struct file_operations memory_fops = {
 738         .open = memory_open,
 739         .llseek = noop_llseek,
 740 };
 741
 742 static char *mem_devnode(const struct device *dev, umode_t *mode)
 743 {
 744         if (mode && devlist[MINOR(dev->devt)].mode)
 745                 *mode = devlist[MINOR(dev->devt)].mode;
 746         return NULL;
 747 }
 748
 749 static const struct class mem_class = {
 750         .name           = "mem",
 751         .devnode        = mem_devnode,
 752 };
 753
 754 static int __init chr_dev_init(void)
 755 {
 756         int retval;
 757         int minor;
 758
 759         if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
 760                 printk("unable to get major %d for memory devs\n", MEM_MAJOR);
 761
 762         retval = class_register(&mem_class);
 763         if (retval)
 764                 return retval;
 765
 766         for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
 767                 if (!devlist[minor].name)
 768                         continue;
 769
 770                 /*
 771                  * Create /dev/port?
 772                  */
 773                 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
 774                         continue;
 775
 776                 device_create(&mem_class, NULL, MKDEV(MEM_MAJOR, minor),
 777                               NULL, devlist[minor].name);
 778         }
 779
 780         return tty_init();
 781 }
 782
 783 fs_initcall(chr_dev_init);