drivers/char/mem.c

   1 /*
   2  *  linux/drivers/char/mem.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  *  Added devfs support.
   7  *    Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
   8  *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/miscdevice.h>
  13 #include <linux/slab.h>
  14 #include <linux/vmalloc.h>
  15 #include <linux/mman.h>
  16 #include <linux/random.h>
  17 #include <linux/init.h>
  18 #include <linux/raw.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/splice.h>
  26 #include <linux/pfn.h>
  27 #include <linux/export.h>
  28 #include <linux/io.h>
  29 #include <linux/aio.h>
  30
  31 #include <asm/uaccess.h>
  32
  33 #ifdef CONFIG_IA64
  34 # include <linux/efi.h>
  35 #endif
  36
  37 #define DEVPORT_MINOR   4
  38
  39 static inline unsigned long size_inside_page(unsigned long start,
  40                                              unsigned long size)
  41 {
  42         unsigned long sz;
  43
  44         sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));
  45
  46         return min(sz, size);
  47 }
  48
  49 #ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE
  50 static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
  51 {
  52         return addr + count <= __pa(high_memory);
  53 }
  54
  55 static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
  56 {
  57         return 1;
  58 }
  59 #endif
  60
  61 #ifdef CONFIG_STRICT_DEVMEM
  62 static inline int range_is_allowed(unsigned long pfn, unsigned long size)
  63 {
  64         u64 from = ((u64)pfn) << PAGE_SHIFT;
  65         u64 to = from + size;
  66         u64 cursor = from;
  67
  68         while (cursor < to) {
  69                 if (!devmem_is_allowed(pfn)) {
  70                         printk(KERN_INFO
  71                 "Program %s tried to access /dev/mem between %Lx->%Lx.\n",
  72                                 current->comm, from, to);
  73                         return 0;
  74                 }
  75                 cursor += PAGE_SIZE;
  76                 pfn++;
  77         }
  78         return 1;
  79 }
  80 #else
  81 static inline int range_is_allowed(unsigned long pfn, unsigned long size)
  82 {
  83         return 1;
  84 }
  85 #endif
  86
  87 void __weak unxlate_dev_mem_ptr(unsigned long phys, void *addr)
  88 {
  89 }
  90
  91 /*
  92  * This funcion reads the *physical* memory. The f_pos points directly to the
  93  * memory location.
  94  */
  95 static ssize_t read_mem(struct file *file, char __user *buf,
  96                         size_t count, loff_t *ppos)
  97 {
  98         phys_addr_t p = *ppos;
  99         ssize_t read, sz;
 100         char *ptr;
 101
 102         if (p != *ppos)
 103                 return 0;
 104
 105         if (!valid_phys_addr_range(p, count))
 106                 return -EFAULT;
 107         read = 0;
 108 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 109         /* we don't have page 0 mapped on sparc and m68k.. */
 110         if (p < PAGE_SIZE) {
 111                 sz = size_inside_page(p, count);
 112                 if (sz > 0) {
 113                         if (clear_user(buf, sz))
 114                                 return -EFAULT;
 115                         buf += sz;
 116                         p += sz;
 117                         count -= sz;
 118                         read += sz;
 119                 }
 120         }
 121 #endif
 122
 123         while (count > 0) {
 124                 unsigned long remaining;
 125
 126                 sz = size_inside_page(p, count);
 127
 128                 if (!range_is_allowed(p >> PAGE_SHIFT, count))
 129                         return -EPERM;
 130
 131                 /*
 132                  * On ia64 if a page has been mapped somewhere as uncached, then
 133                  * it must also be accessed uncached by the kernel or data
 134                  * corruption may occur.
 135                  */
 136                 ptr = xlate_dev_mem_ptr(p);
 137                 if (!ptr)
 138                         return -EFAULT;
 139
 140                 remaining = copy_to_user(buf, ptr, sz);
 141                 unxlate_dev_mem_ptr(p, ptr);
 142                 if (remaining)
 143                         return -EFAULT;
 144
 145                 buf += sz;
 146                 p += sz;
 147                 count -= sz;
 148                 read += sz;
 149         }
 150
 151         *ppos += read;
 152         return read;
 153 }
 154
 155 static ssize_t write_mem(struct file *file, const char __user *buf,
 156                          size_t count, loff_t *ppos)
 157 {
 158         phys_addr_t p = *ppos;
 159         ssize_t written, sz;
 160         unsigned long copied;
 161         void *ptr;
 162
 163         if (p != *ppos)
 164                 return -EFBIG;
 165
 166         if (!valid_phys_addr_range(p, count))
 167                 return -EFAULT;
 168
 169         written = 0;
 170
 171 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 172         /* we don't have page 0 mapped on sparc and m68k.. */
 173         if (p < PAGE_SIZE) {
 174                 sz = size_inside_page(p, count);
 175                 /* Hmm. Do something? */
 176                 buf += sz;
 177                 p += sz;
 178                 count -= sz;
 179                 written += sz;
 180         }
 181 #endif
 182
 183         while (count > 0) {
 184                 sz = size_inside_page(p, count);
 185
 186                 if (!range_is_allowed(p >> PAGE_SHIFT, sz))
 187                         return -EPERM;
 188
 189                 /*
 190                  * On ia64 if a page has been mapped somewhere as uncached, then
 191                  * it must also be accessed uncached by the kernel or data
 192                  * corruption may occur.
 193                  */
 194                 ptr = xlate_dev_mem_ptr(p);
 195                 if (!ptr) {
 196                         if (written)
 197                                 break;
 198                         return -EFAULT;
 199                 }
 200
 201                 copied = copy_from_user(ptr, buf, sz);
 202                 unxlate_dev_mem_ptr(p, ptr);
 203                 if (copied) {
 204                         written += sz - copied;
 205                         if (written)
 206                                 break;
 207                         return -EFAULT;
 208                 }
 209
 210                 buf += sz;
 211                 p += sz;
 212                 count -= sz;
 213                 written += sz;
 214         }
 215
 216         *ppos += written;
 217         return written;
 218 }
 219
 220 int __weak phys_mem_access_prot_allowed(struct file *file,
 221         unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
 222 {
 223         return 1;
 224 }
 225
 226 #ifndef __HAVE_PHYS_MEM_ACCESS_PROT
 227
 228 /*
 229  * Architectures vary in how they handle caching for addresses
 230  * outside of main memory.
 231  *
 232  */
 233 #ifdef pgprot_noncached
 234 static int uncached_access(struct file *file, phys_addr_t addr)
 235 {
 236 #if defined(CONFIG_IA64)
 237         /*
 238          * On ia64, we ignore O_DSYNC because we cannot tolerate memory
 239          * attribute aliases.
 240          */
 241         return !(efi_mem_attributes(addr) & EFI_MEMORY_WB);
 242 #elif defined(CONFIG_MIPS)
 243         {
 244                 extern int __uncached_access(struct file *file,
 245                                              unsigned long addr);
 246
 247                 return __uncached_access(file, addr);
 248         }
 249 #else
 250         /*
 251          * Accessing memory above the top the kernel knows about or through a
 252          * file pointer
 253          * that was marked O_DSYNC will be done non-cached.
 254          */
 255         if (file->f_flags & O_DSYNC)
 256                 return 1;
 257         return addr >= __pa(high_memory);
 258 #endif
 259 }
 260 #endif
 261
 262 static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 263                                      unsigned long size, pgprot_t vma_prot)
 264 {
 265 #ifdef pgprot_noncached
 266         phys_addr_t offset = pfn << PAGE_SHIFT;
 267
 268         if (uncached_access(file, offset))
 269                 return pgprot_noncached(vma_prot);
 270 #endif
 271         return vma_prot;
 272 }
 273 #endif
 274
 275 #ifndef CONFIG_MMU
 276 static unsigned long get_unmapped_area_mem(struct file *file,
 277                                            unsigned long addr,
 278                                            unsigned long len,
 279                                            unsigned long pgoff,
 280                                            unsigned long flags)
 281 {
 282         if (!valid_mmap_phys_addr_range(pgoff, len))
 283                 return (unsigned long) -EINVAL;
 284         return pgoff << PAGE_SHIFT;
 285 }
 286
 287 /* can't do an in-place private mapping if there's no MMU */
 288 static inline int private_mapping_ok(struct vm_area_struct *vma)
 289 {
 290         return vma->vm_flags & VM_MAYSHARE;
 291 }
 292 #else
 293 #define get_unmapped_area_mem   NULL
 294
 295 static inline int private_mapping_ok(struct vm_area_struct *vma)
 296 {
 297         return 1;
 298 }
 299 #endif
 300
 301 static const struct vm_operations_struct mmap_mem_ops = {
 302 #ifdef CONFIG_HAVE_IOREMAP_PROT
 303         .access = generic_access_phys
 304 #endif
 305 };
 306
 307 static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 308 {
 309         size_t size = vma->vm_end - vma->vm_start;
 310
 311         if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
 312                 return -EINVAL;
 313
 314         if (!private_mapping_ok(vma))
 315                 return -ENOSYS;
 316
 317         if (!range_is_allowed(vma->vm_pgoff, size))
 318                 return -EPERM;
 319
 320         if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
 321                                                 &vma->vm_page_prot))
 322                 return -EINVAL;
 323
 324         vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
 325                                                  size,
 326                                                  vma->vm_page_prot);
 327
 328         vma->vm_ops = &mmap_mem_ops;
 329
 330         /* Remap-pfn-range will mark the range VM_IO */
 331         if (remap_pfn_range(vma,
 332                             vma->vm_start,
 333                             vma->vm_pgoff,
 334                             size,
 335                             vma->vm_page_prot)) {
 336                 return -EAGAIN;
 337         }
 338         return 0;
 339 }
 340
 341 #ifdef CONFIG_DEVKMEM
 342 static int mmap_kmem(struct file *file, struct vm_area_struct *vma)
 343 {
 344         unsigned long pfn;
 345
 346         /* Turn a kernel-virtual address into a physical page frame */
 347         pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT;
 348
 349         /*
 350          * RED-PEN: on some architectures there is more mapped memory than
 351          * available in mem_map which pfn_valid checks for. Perhaps should add a
 352          * new macro here.
 353          *
 354          * RED-PEN: vmalloc is not supported right now.
 355          */
 356         if (!pfn_valid(pfn))
 357                 return -EIO;
 358
 359         vma->vm_pgoff = pfn;
 360         return mmap_mem(file, vma);
 361 }
 362 #endif
 363
 364 #ifdef CONFIG_DEVKMEM
 365 /*
 366  * This function reads the *virtual* memory as seen by the kernel.
 367  */
 368 static ssize_t read_kmem(struct file *file, char __user *buf,
 369                          size_t count, loff_t *ppos)
 370 {
 371         unsigned long p = *ppos;
 372         ssize_t low_count, read, sz;
 373         char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
 374         int err = 0;
 375
 376         read = 0;
 377         if (p < (unsigned long) high_memory) {
 378                 low_count = count;
 379                 if (count > (unsigned long)high_memory - p)
 380                         low_count = (unsigned long)high_memory - p;
 381
 382 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 383                 /* we don't have page 0 mapped on sparc and m68k.. */
 384                 if (p < PAGE_SIZE && low_count > 0) {
 385                         sz = size_inside_page(p, low_count);
 386                         if (clear_user(buf, sz))
 387                                 return -EFAULT;
 388                         buf += sz;
 389                         p += sz;
 390                         read += sz;
 391                         low_count -= sz;
 392                         count -= sz;
 393                 }
 394 #endif
 395                 while (low_count > 0) {
 396                         sz = size_inside_page(p, low_count);
 397
 398                         /*
 399                          * On ia64 if a page has been mapped somewhere as
 400                          * uncached, then it must also be accessed uncached
 401                          * by the kernel or data corruption may occur
 402                          */
 403                         kbuf = xlate_dev_kmem_ptr((char *)p);
 404
 405                         if (copy_to_user(buf, kbuf, sz))
 406                                 return -EFAULT;
 407                         buf += sz;
 408                         p += sz;
 409                         read += sz;
 410                         low_count -= sz;
 411                         count -= sz;
 412                 }
 413         }
 414
 415         if (count > 0) {
 416                 kbuf = (char *)__get_free_page(GFP_KERNEL);
 417                 if (!kbuf)
 418                         return -ENOMEM;
 419                 while (count > 0) {
 420                         sz = size_inside_page(p, count);
 421                         if (!is_vmalloc_or_module_addr((void *)p)) {
 422                                 err = -ENXIO;
 423                                 break;
 424                         }
 425                         sz = vread(kbuf, (char *)p, sz);
 426                         if (!sz)
 427                                 break;
 428                         if (copy_to_user(buf, kbuf, sz)) {
 429                                 err = -EFAULT;
 430                                 break;
 431                         }
 432                         count -= sz;
 433                         buf += sz;
 434                         read += sz;
 435                         p += sz;
 436                 }
 437                 free_page((unsigned long)kbuf);
 438         }
 439         *ppos = p;
 440         return read ? read : err;
 441 }
 442
 443
 444 static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
 445                                 size_t count, loff_t *ppos)
 446 {
 447         ssize_t written, sz;
 448         unsigned long copied;
 449
 450         written = 0;
 451 #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
 452         /* we don't have page 0 mapped on sparc and m68k.. */
 453         if (p < PAGE_SIZE) {
 454                 sz = size_inside_page(p, count);
 455                 /* Hmm. Do something? */
 456                 buf += sz;
 457                 p += sz;
 458                 count -= sz;
 459                 written += sz;
 460         }
 461 #endif
 462
 463         while (count > 0) {
 464                 char *ptr;
 465
 466                 sz = size_inside_page(p, count);
 467
 468                 /*
 469                  * On ia64 if a page has been mapped somewhere as uncached, then
 470                  * it must also be accessed uncached by the kernel or data
 471                  * corruption may occur.
 472                  */
 473                 ptr = xlate_dev_kmem_ptr((char *)p);
 474
 475                 copied = copy_from_user(ptr, buf, sz);
 476                 if (copied) {
 477                         written += sz - copied;
 478                         if (written)
 479                                 break;
 480                         return -EFAULT;
 481                 }
 482                 buf += sz;
 483                 p += sz;
 484                 count -= sz;
 485                 written += sz;
 486         }
 487
 488         *ppos += written;
 489         return written;
 490 }
 491
 492 /*
 493  * This function writes to the *virtual* memory as seen by the kernel.
 494  */
 495 static ssize_t write_kmem(struct file *file, const char __user *buf,
 496                           size_t count, loff_t *ppos)
 497 {
 498         unsigned long p = *ppos;
 499         ssize_t wrote = 0;
 500         ssize_t virtr = 0;
 501         char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
 502         int err = 0;
 503
 504         if (p < (unsigned long) high_memory) {
 505                 unsigned long to_write = min_t(unsigned long, count,
 506                                                (unsigned long)high_memory - p);
 507                 wrote = do_write_kmem(p, buf, to_write, ppos);
 508                 if (wrote != to_write)
 509                         return wrote;
 510                 p += wrote;
 511                 buf += wrote;
 512                 count -= wrote;
 513         }
 514
 515         if (count > 0) {
 516                 kbuf = (char *)__get_free_page(GFP_KERNEL);
 517                 if (!kbuf)
 518                         return wrote ? wrote : -ENOMEM;
 519                 while (count > 0) {
 520                         unsigned long sz = size_inside_page(p, count);
 521                         unsigned long n;
 522
 523                         if (!is_vmalloc_or_module_addr((void *)p)) {
 524                                 err = -ENXIO;
 525                                 break;
 526                         }
 527                         n = copy_from_user(kbuf, buf, sz);
 528                         if (n) {
 529                                 err = -EFAULT;
 530                                 break;
 531                         }
 532                         vwrite(kbuf, (char *)p, sz);
 533                         count -= sz;
 534                         buf += sz;
 535                         virtr += sz;
 536                         p += sz;
 537                 }
 538                 free_page((unsigned long)kbuf);
 539         }
 540
 541         *ppos = p;
 542         return virtr + wrote ? : err;
 543 }
 544 #endif
 545
 546 #ifdef CONFIG_DEVPORT
 547 static ssize_t read_port(struct file *file, char __user *buf,
 548                          size_t count, loff_t *ppos)
 549 {
 550         unsigned long i = *ppos;
 551         char __user *tmp = buf;
 552
 553         if (!access_ok(VERIFY_WRITE, buf, count))
 554                 return -EFAULT;
 555         while (count-- > 0 && i < 65536) {
 556                 if (__put_user(inb(i), tmp) < 0)
 557                         return -EFAULT;
 558                 i++;
 559                 tmp++;
 560         }
 561         *ppos = i;
 562         return tmp-buf;
 563 }
 564
 565 static ssize_t write_port(struct file *file, const char __user *buf,
 566                           size_t count, loff_t *ppos)
 567 {
 568         unsigned long i = *ppos;
 569         const char __user *tmp = buf;
 570
 571         if (!access_ok(VERIFY_READ, buf, count))
 572                 return -EFAULT;
 573         while (count-- > 0 && i < 65536) {
 574                 char c;
 575                 if (__get_user(c, tmp)) {
 576                         if (tmp > buf)
 577                                 break;
 578                         return -EFAULT;
 579                 }
 580                 outb(c, i);
 581                 i++;
 582                 tmp++;
 583         }
 584         *ppos = i;
 585         return tmp-buf;
 586 }
 587 #endif
 588
 589 static ssize_t read_null(struct file *file, char __user *buf,
 590                          size_t count, loff_t *ppos)
 591 {
 592         return 0;
 593 }
 594
 595 static ssize_t write_null(struct file *file, const char __user *buf,
 596                           size_t count, loff_t *ppos)
 597 {
 598         return count;
 599 }
 600
 601 static ssize_t aio_read_null(struct kiocb *iocb, const struct iovec *iov,
 602                              unsigned long nr_segs, loff_t pos)
 603 {
 604         return 0;
 605 }
 606
 607 static ssize_t aio_write_null(struct kiocb *iocb, const struct iovec *iov,
 608                               unsigned long nr_segs, loff_t pos)
 609 {
 610         return iov_length(iov, nr_segs);
 611 }
 612
 613 static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
 614                         struct splice_desc *sd)
 615 {
 616         return sd->len;
 617 }
 618
 619 static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
 620                                  loff_t *ppos, size_t len, unsigned int flags)
 621 {
 622         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
 623 }
 624
 625 static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
 626 {
 627         size_t written = 0;
 628
 629         while (iov_iter_count(iter)) {
 630                 size_t chunk = iov_iter_count(iter), n;
 631                 if (chunk > PAGE_SIZE)
 632                         chunk = PAGE_SIZE;      /* Just for latency reasons */
 633                 n = iov_iter_zero(chunk, iter);
 634                 if (!n && iov_iter_count(iter))
 635                         return written ? written : -EFAULT;
 636                 written += n;
 637                 if (signal_pending(current))
 638                         return written ? written : -ERESTARTSYS;
 639                 cond_resched();
 640         }
 641         return written;
 642 }
 643
 644 static int mmap_zero(struct file *file, struct vm_area_struct *vma)
 645 {
 646 #ifndef CONFIG_MMU
 647         return -ENOSYS;
 648 #endif
 649         if (vma->vm_flags & VM_SHARED)
 650                 return shmem_zero_setup(vma);
 651         return 0;
 652 }
 653
 654 static ssize_t write_full(struct file *file, const char __user *buf,
 655                           size_t count, loff_t *ppos)
 656 {
 657         return -ENOSPC;
 658 }
 659
 660 /*
 661  * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
 662  * can fopen() both devices with "a" now.  This was previously impossible.
 663  * -- SRB.
 664  */
 665 static loff_t null_lseek(struct file *file, loff_t offset, int orig)
 666 {
 667         return file->f_pos = 0;
 668 }
 669
 670 /*
 671  * The memory devices use the full 32/64 bits of the offset, and so we cannot
 672  * check against negative addresses: they are ok. The return value is weird,
 673  * though, in that case (0).
 674  *
 675  * also note that seeking relative to the "end of file" isn't supported:
 676  * it has no meaning, so it returns -EINVAL.
 677  */
 678 static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 679 {
 680         loff_t ret;
 681
 682         mutex_lock(&file_inode(file)->i_mutex);
 683         switch (orig) {
 684         case SEEK_CUR:
 685                 offset += file->f_pos;
 686         case SEEK_SET:
 687                 /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
 688                 if (IS_ERR_VALUE((unsigned long long)offset)) {
 689                         ret = -EOVERFLOW;
 690                         break;
 691                 }
 692                 file->f_pos = offset;
 693                 ret = file->f_pos;
 694                 force_successful_syscall_return();
 695                 break;
 696         default:
 697                 ret = -EINVAL;
 698         }
 699         mutex_unlock(&file_inode(file)->i_mutex);
 700         return ret;
 701 }
 702
 703 static int open_port(struct inode *inode, struct file *filp)
 704 {
 705         return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
 706 }
 707
 708 #define zero_lseek      null_lseek
 709 #define full_lseek      null_lseek
 710 #define write_zero      write_null
 711 #define aio_write_zero  aio_write_null
 712 #define open_mem        open_port
 713 #define open_kmem       open_mem
 714
 715 static const struct file_operations mem_fops = {
 716         .llseek         = memory_lseek,
 717         .read           = read_mem,
 718         .write          = write_mem,
 719         .mmap           = mmap_mem,
 720         .open           = open_mem,
 721         .get_unmapped_area = get_unmapped_area_mem,
 722 };
 723
 724 #ifdef CONFIG_DEVKMEM
 725 static const struct file_operations kmem_fops = {
 726         .llseek         = memory_lseek,
 727         .read           = read_kmem,
 728         .write          = write_kmem,
 729         .mmap           = mmap_kmem,
 730         .open           = open_kmem,
 731         .get_unmapped_area = get_unmapped_area_mem,
 732 };
 733 #endif
 734
 735 static const struct file_operations null_fops = {
 736         .llseek         = null_lseek,
 737         .read           = read_null,
 738         .write          = write_null,
 739         .aio_read       = aio_read_null,
 740         .aio_write      = aio_write_null,
 741         .splice_write   = splice_write_null,
 742 };
 743
 744 #ifdef CONFIG_DEVPORT
 745 static const struct file_operations port_fops = {
 746         .llseek         = memory_lseek,
 747         .read           = read_port,
 748         .write          = write_port,
 749         .open           = open_port,
 750 };
 751 #endif
 752
 753 static const struct file_operations zero_fops = {
 754         .llseek         = zero_lseek,
 755         .read           = new_sync_read,
 756         .write          = write_zero,
 757         .read_iter      = read_iter_zero,
 758         .aio_write      = aio_write_zero,
 759         .mmap           = mmap_zero,
 760 };
 761
 762 /*
 763  * capabilities for /dev/zero
 764  * - permits private mappings, "copies" are taken of the source of zeros
 765  * - no writeback happens
 766  */
 767 static struct backing_dev_info zero_bdi = {
 768         .name           = "char/mem",
 769         .capabilities   = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
 770 };
 771
 772 static const struct file_operations full_fops = {
 773         .llseek         = full_lseek,
 774         .read           = new_sync_read,
 775         .read_iter      = read_iter_zero,
 776         .write          = write_full,
 777 };
 778
 779 static const struct memdev {
 780         const char *name;
 781         umode_t mode;
 782         const struct file_operations *fops;
 783         struct backing_dev_info *dev_info;
 784 } devlist[] = {
 785          [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },
 786 #ifdef CONFIG_DEVKMEM
 787          [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },
 788 #endif
 789          [3] = { "null", 0666, &null_fops, NULL },
 790 #ifdef CONFIG_DEVPORT
 791          [4] = { "port", 0, &port_fops, NULL },
 792 #endif
 793          [5] = { "zero", 0666, &zero_fops, &zero_bdi },
 794          [7] = { "full", 0666, &full_fops, NULL },
 795          [8] = { "random", 0666, &random_fops, NULL },
 796          [9] = { "urandom", 0666, &urandom_fops, NULL },
 797 #ifdef CONFIG_PRINTK
 798         [11] = { "kmsg", 0644, &kmsg_fops, NULL },
 799 #endif
 800 };
 801
 802 static int memory_open(struct inode *inode, struct file *filp)
 803 {
 804         int minor;
 805         const struct memdev *dev;
 806
 807         minor = iminor(inode);
 808         if (minor >= ARRAY_SIZE(devlist))
 809                 return -ENXIO;
 810
 811         dev = &devlist[minor];
 812         if (!dev->fops)
 813                 return -ENXIO;
 814
 815         filp->f_op = dev->fops;
 816         if (dev->dev_info)
 817                 filp->f_mapping->backing_dev_info = dev->dev_info;
 818
 819         /* Is /dev/mem or /dev/kmem ? */
 820         if (dev->dev_info == &directly_mappable_cdev_bdi)
 821                 filp->f_mode |= FMODE_UNSIGNED_OFFSET;
 822
 823         if (dev->fops->open)
 824                 return dev->fops->open(inode, filp);
 825
 826         return 0;
 827 }
 828
 829 static const struct file_operations memory_fops = {
 830         .open = memory_open,
 831         .llseek = noop_llseek,
 832 };
 833
 834 static char *mem_devnode(struct device *dev, umode_t *mode)
 835 {
 836         if (mode && devlist[MINOR(dev->devt)].mode)
 837                 *mode = devlist[MINOR(dev->devt)].mode;
 838         return NULL;
 839 }
 840
 841 static struct class *mem_class;
 842
 843 static int __init chr_dev_init(void)
 844 {
 845         int minor;
 846         int err;
 847
 848         err = bdi_init(&zero_bdi);
 849         if (err)
 850                 return err;
 851
 852         if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
 853                 printk("unable to get major %d for memory devs\n", MEM_MAJOR);
 854
 855         mem_class = class_create(THIS_MODULE, "mem");
 856         if (IS_ERR(mem_class))
 857                 return PTR_ERR(mem_class);
 858
 859         mem_class->devnode = mem_devnode;
 860         for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
 861                 if (!devlist[minor].name)
 862                         continue;
 863
 864                 /*
 865                  * Create /dev/port?
 866                  */
 867                 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
 868                         continue;
 869
 870                 device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
 871                               NULL, devlist[minor].name);
 872         }
 873
 874         return tty_init();
 875 }
 876
 877 fs_initcall(chr_dev_init);