/*
   *  linux/drivers/char/mem.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *

   *  Added devfs support.

   *    Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>

   *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>

   */

  #include <linux/mm.h>
  #include <linux/miscdevice.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <linux/mman.h>
  #include <linux/random.h>
  #include <linux/init.h>
  #include <linux/raw.h>
  #include <linux/tty.h>
  #include <linux/capability.h>

  #include <linux/ptrace.h>
  #include <linux/device.h>

  #include <linux/highmem.h>

  #include <linux/backing-dev.h>

  #include <linux/splice.h>

  #include <linux/pfn.h>

  #include <linux/export.h>

  #include <linux/io.h>

  #include <linux/aio.h>

  
  #include <asm/uaccess.h>

  
  #ifdef CONFIG_IA64
  # include <linux/efi.h>
  #endif

  #define DEVPORT_MINOR	4

  static inline unsigned long size_inside_page(unsigned long start,
  					     unsigned long size)
  {
  	unsigned long sz;

  	sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));

  	return min(sz, size);

  }

  #ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE

  static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)

  {

  	return addr + count <= __pa(high_memory);

  }

  static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)

  {
  	return 1;
  }

  #endif

  #ifdef CONFIG_STRICT_DEVMEM

  static inline int range_is_allowed(unsigned long pfn, unsigned long size)

  {

  	u64 from = ((u64)pfn) << PAGE_SHIFT;
  	u64 to = from + size;
  	u64 cursor = from;
  
  	while (cursor < to) {
  		if (!devmem_is_allowed(pfn)) {
  			printk(KERN_INFO
  		"Program %s tried to access /dev/mem between %Lx->%Lx.
  ",

  				current->comm, from, to);
  			return 0;
  		}

  		cursor += PAGE_SIZE;
  		pfn++;

  	}
  	return 1;
  }
  #else

  static inline int range_is_allowed(unsigned long pfn, unsigned long size)

  {
  	return 1;
  }
  #endif

  void __weak unxlate_dev_mem_ptr(unsigned long phys, void *addr)

  {
  }

  /*

   * This funcion reads the *physical* memory. The f_pos points directly to the
   * memory location.

   */

  static ssize_t read_mem(struct file *file, char __user *buf,

  			size_t count, loff_t *ppos)
  {

  	phys_addr_t p = *ppos;

  	ssize_t read, sz;
  	char *ptr;

  	if (p != *ppos)
  		return 0;

  	if (!valid_phys_addr_range(p, count))

  		return -EFAULT;
  	read = 0;
  #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
  	/* we don't have page 0 mapped on sparc and m68k.. */
  	if (p < PAGE_SIZE) {

  		sz = size_inside_page(p, count);

  		if (sz > 0) {
  			if (clear_user(buf, sz))
  				return -EFAULT;

  			buf += sz;
  			p += sz;
  			count -= sz;
  			read += sz;

  		}
  	}
  #endif
  
  	while (count > 0) {

  		unsigned long remaining;

  		sz = size_inside_page(p, count);

  		if (!range_is_allowed(p >> PAGE_SHIFT, count))
  			return -EPERM;

  		/*

  		 * On ia64 if a page has been mapped somewhere as uncached, then
  		 * it must also be accessed uncached by the kernel or data
  		 * corruption may occur.

  		 */
  		ptr = xlate_dev_mem_ptr(p);

  		if (!ptr)
  			return -EFAULT;

  		remaining = copy_to_user(buf, ptr, sz);

  		unxlate_dev_mem_ptr(p, ptr);

  		if (remaining)
  			return -EFAULT;

  		buf += sz;
  		p += sz;
  		count -= sz;
  		read += sz;
  	}
  
  	*ppos += read;
  	return read;
  }

  static ssize_t write_mem(struct file *file, const char __user *buf,

  			 size_t count, loff_t *ppos)
  {

  	phys_addr_t p = *ppos;

  	ssize_t written, sz;
  	unsigned long copied;
  	void *ptr;

  	if (p != *ppos)
  		return -EFBIG;

  	if (!valid_phys_addr_range(p, count))

  		return -EFAULT;
  
  	written = 0;
  
  #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
  	/* we don't have page 0 mapped on sparc and m68k.. */
  	if (p < PAGE_SIZE) {

  		sz = size_inside_page(p, count);

  		/* Hmm. Do something? */
  		buf += sz;
  		p += sz;
  		count -= sz;
  		written += sz;
  	}
  #endif
  
  	while (count > 0) {

  		sz = size_inside_page(p, count);

  		if (!range_is_allowed(p >> PAGE_SHIFT, sz))
  			return -EPERM;

  		/*

  		 * On ia64 if a page has been mapped somewhere as uncached, then
  		 * it must also be accessed uncached by the kernel or data
  		 * corruption may occur.

  		 */
  		ptr = xlate_dev_mem_ptr(p);

  		if (!ptr) {
  			if (written)
  				break;
  			return -EFAULT;
  		}

  
  		copied = copy_from_user(ptr, buf, sz);

  		unxlate_dev_mem_ptr(p, ptr);

  		if (copied) {

  			written += sz - copied;
  			if (written)
  				break;

  			return -EFAULT;
  		}

  		buf += sz;
  		p += sz;
  		count -= sz;
  		written += sz;
  	}
  
  	*ppos += written;
  	return written;
  }

  int __weak phys_mem_access_prot_allowed(struct file *file,

  	unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
  {
  	return 1;
  }

  #ifndef __HAVE_PHYS_MEM_ACCESS_PROT

  
  /*
   * Architectures vary in how they handle caching for addresses
   * outside of main memory.
   *
   */

  #ifdef pgprot_noncached

  static int uncached_access(struct file *file, phys_addr_t addr)

  {
  #if defined(CONFIG_IA64)
  	/*
  	 * On ia64, we ignore O_DSYNC because we cannot tolerate memory
  	 * attribute aliases.
  	 */
  	return !(efi_mem_attributes(addr) & EFI_MEMORY_WB);
  #elif defined(CONFIG_MIPS)
  	{
  		extern int __uncached_access(struct file *file,
  					     unsigned long addr);
  
  		return __uncached_access(file, addr);
  	}
  #else
  	/*
  	 * Accessing memory above the top the kernel knows about or through a
  	 * file pointer
  	 * that was marked O_DSYNC will be done non-cached.
  	 */
  	if (file->f_flags & O_DSYNC)
  		return 1;
  	return addr >= __pa(high_memory);
  #endif
  }

  #endif

  static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
  				     unsigned long size, pgprot_t vma_prot)
  {
  #ifdef pgprot_noncached

  	phys_addr_t offset = pfn << PAGE_SHIFT;

  
  	if (uncached_access(file, offset))
  		return pgprot_noncached(vma_prot);
  #endif
  	return vma_prot;
  }
  #endif

  #ifndef CONFIG_MMU
  static unsigned long get_unmapped_area_mem(struct file *file,
  					   unsigned long addr,
  					   unsigned long len,
  					   unsigned long pgoff,
  					   unsigned long flags)
  {
  	if (!valid_mmap_phys_addr_range(pgoff, len))
  		return (unsigned long) -EINVAL;

  	return pgoff << PAGE_SHIFT;

  }
  
  /* can't do an in-place private mapping if there's no MMU */
  static inline int private_mapping_ok(struct vm_area_struct *vma)
  {
  	return vma->vm_flags & VM_MAYSHARE;
  }
  #else
  #define get_unmapped_area_mem	NULL
  
  static inline int private_mapping_ok(struct vm_area_struct *vma)
  {
  	return 1;
  }
  #endif

  static const struct vm_operations_struct mmap_mem_ops = {

  #ifdef CONFIG_HAVE_IOREMAP_PROT
  	.access = generic_access_phys
  #endif

  };

  static int mmap_mem(struct file *file, struct vm_area_struct *vma)

  {

  	size_t size = vma->vm_end - vma->vm_start;

  	if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))

  		return -EINVAL;

  	if (!private_mapping_ok(vma))
  		return -ENOSYS;

  	if (!range_is_allowed(vma->vm_pgoff, size))
  		return -EPERM;

  	if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
  						&vma->vm_page_prot))
  		return -EINVAL;

  	vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,

  						 size,

  						 vma->vm_page_prot);

  	vma->vm_ops = &mmap_mem_ops;

  	/* Remap-pfn-range will mark the range VM_IO */

  	if (remap_pfn_range(vma,
  			    vma->vm_start,
  			    vma->vm_pgoff,

  			    size,

  			    vma->vm_page_prot)) {

  		return -EAGAIN;

  	}

  	return 0;
  }

  #ifdef CONFIG_DEVKMEM

  static int mmap_kmem(struct file *file, struct vm_area_struct *vma)

  {

  	unsigned long pfn;

  	/* Turn a kernel-virtual address into a physical page frame */
  	pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT;

  	/*

  	 * RED-PEN: on some architectures there is more mapped memory than
  	 * available in mem_map which pfn_valid checks for. Perhaps should add a
  	 * new macro here.

  	 *
  	 * RED-PEN: vmalloc is not supported right now.
  	 */

  	if (!pfn_valid(pfn))

  		return -EIO;

  
  	vma->vm_pgoff = pfn;

  	return mmap_mem(file, vma);
  }

  #endif

  #ifdef CONFIG_DEVKMEM

  /*
   * This function reads the *virtual* memory as seen by the kernel.
   */

  static ssize_t read_kmem(struct file *file, char __user *buf,

  			 size_t count, loff_t *ppos)
  {
  	unsigned long p = *ppos;
  	ssize_t low_count, read, sz;

  	char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */

  	int err = 0;

  
  	read = 0;
  	if (p < (unsigned long) high_memory) {
  		low_count = count;

  		if (count > (unsigned long)high_memory - p)
  			low_count = (unsigned long)high_memory - p;

  
  #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
  		/* we don't have page 0 mapped on sparc and m68k.. */
  		if (p < PAGE_SIZE && low_count > 0) {

  			sz = size_inside_page(p, low_count);
  			if (clear_user(buf, sz))

  				return -EFAULT;

  			buf += sz;
  			p += sz;
  			read += sz;
  			low_count -= sz;
  			count -= sz;

  		}
  #endif
  		while (low_count > 0) {

  			sz = size_inside_page(p, low_count);

  
  			/*
  			 * On ia64 if a page has been mapped somewhere as
  			 * uncached, then it must also be accessed uncached
  			 * by the kernel or data corruption may occur
  			 */
  			kbuf = xlate_dev_kmem_ptr((char *)p);
  
  			if (copy_to_user(buf, kbuf, sz))
  				return -EFAULT;
  			buf += sz;
  			p += sz;
  			read += sz;
  			low_count -= sz;
  			count -= sz;
  		}
  	}
  
  	if (count > 0) {
  		kbuf = (char *)__get_free_page(GFP_KERNEL);
  		if (!kbuf)
  			return -ENOMEM;
  		while (count > 0) {

  			sz = size_inside_page(p, count);

  			if (!is_vmalloc_or_module_addr((void *)p)) {
  				err = -ENXIO;
  				break;
  			}

  			sz = vread(kbuf, (char *)p, sz);
  			if (!sz)

  				break;

  			if (copy_to_user(buf, kbuf, sz)) {

  				err = -EFAULT;
  				break;

  			}

  			count -= sz;
  			buf += sz;
  			read += sz;
  			p += sz;

  		}
  		free_page((unsigned long)kbuf);
  	}

  	*ppos = p;
  	return read ? read : err;

  }

  static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
  				size_t count, loff_t *ppos)

  {
  	ssize_t written, sz;
  	unsigned long copied;
  
  	written = 0;
  #ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
  	/* we don't have page 0 mapped on sparc and m68k.. */

  	if (p < PAGE_SIZE) {
  		sz = size_inside_page(p, count);

  		/* Hmm. Do something? */
  		buf += sz;
  		p += sz;

  		count -= sz;
  		written += sz;
  	}
  #endif
  
  	while (count > 0) {
  		char *ptr;

  		sz = size_inside_page(p, count);

  
  		/*

  		 * On ia64 if a page has been mapped somewhere as uncached, then
  		 * it must also be accessed uncached by the kernel or data
  		 * corruption may occur.

  		 */

  		ptr = xlate_dev_kmem_ptr((char *)p);

  
  		copied = copy_from_user(ptr, buf, sz);
  		if (copied) {

  			written += sz - copied;
  			if (written)
  				break;

  			return -EFAULT;
  		}
  		buf += sz;
  		p += sz;

  		count -= sz;
  		written += sz;
  	}
  
  	*ppos += written;
  	return written;
  }

  /*
   * This function writes to the *virtual* memory as seen by the kernel.
   */

  static ssize_t write_kmem(struct file *file, const char __user *buf,

  			  size_t count, loff_t *ppos)
  {
  	unsigned long p = *ppos;
  	ssize_t wrote = 0;
  	ssize_t virtr = 0;

  	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */

  	int err = 0;

  
  	if (p < (unsigned long) high_memory) {

  		unsigned long to_write = min_t(unsigned long, count,
  					       (unsigned long)high_memory - p);

  		wrote = do_write_kmem(p, buf, to_write, ppos);

  		if (wrote != to_write)
  			return wrote;

  		p += wrote;
  		buf += wrote;
  		count -= wrote;
  	}
  
  	if (count > 0) {
  		kbuf = (char *)__get_free_page(GFP_KERNEL);
  		if (!kbuf)
  			return wrote ? wrote : -ENOMEM;
  		while (count > 0) {

  			unsigned long sz = size_inside_page(p, count);
  			unsigned long n;

  			if (!is_vmalloc_or_module_addr((void *)p)) {
  				err = -ENXIO;
  				break;
  			}

  			n = copy_from_user(kbuf, buf, sz);
  			if (n) {

  				err = -EFAULT;
  				break;

  			}

  			vwrite(kbuf, (char *)p, sz);

  			count -= sz;
  			buf += sz;
  			virtr += sz;
  			p += sz;

  		}
  		free_page((unsigned long)kbuf);
  	}

  	*ppos = p;
  	return virtr + wrote ? : err;

  }

  #endif

  #ifdef CONFIG_DEVPORT

  static ssize_t read_port(struct file *file, char __user *buf,

  			 size_t count, loff_t *ppos)
  {
  	unsigned long i = *ppos;
  	char __user *tmp = buf;
  
  	if (!access_ok(VERIFY_WRITE, buf, count))

  		return -EFAULT;

  	while (count-- > 0 && i < 65536) {

  		if (__put_user(inb(i), tmp) < 0)
  			return -EFAULT;

  		i++;
  		tmp++;
  	}
  	*ppos = i;
  	return tmp-buf;
  }

  static ssize_t write_port(struct file *file, const char __user *buf,

  			  size_t count, loff_t *ppos)
  {
  	unsigned long i = *ppos;

  	const char __user *tmp = buf;

  	if (!access_ok(VERIFY_READ, buf, count))

  		return -EFAULT;
  	while (count-- > 0 && i < 65536) {
  		char c;

  		if (__get_user(c, tmp)) {
  			if (tmp > buf)
  				break;

  			return -EFAULT;

  		}

  		outb(c, i);

  		i++;
  		tmp++;
  	}
  	*ppos = i;
  	return tmp-buf;
  }
  #endif

  static ssize_t read_null(struct file *file, char __user *buf,

  			 size_t count, loff_t *ppos)
  {
  	return 0;
  }

  static ssize_t write_null(struct file *file, const char __user *buf,

  			  size_t count, loff_t *ppos)
  {
  	return count;
  }

  static ssize_t aio_read_null(struct kiocb *iocb, const struct iovec *iov,
  			     unsigned long nr_segs, loff_t pos)
  {
  	return 0;
  }
  
  static ssize_t aio_write_null(struct kiocb *iocb, const struct iovec *iov,
  			      unsigned long nr_segs, loff_t pos)
  {
  	return iov_length(iov, nr_segs);
  }

  static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
  			struct splice_desc *sd)
  {
  	return sd->len;
  }

  static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,

  				 loff_t *ppos, size_t len, unsigned int flags)
  {
  	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
  }

  static ssize_t read_zero(struct file *file, char __user *buf,

  			 size_t count, loff_t *ppos)
  {

  	size_t written;

  
  	if (!count)
  		return 0;
  
  	if (!access_ok(VERIFY_WRITE, buf, count))
  		return -EFAULT;

  	written = 0;
  	while (count) {
  		unsigned long unwritten;
  		size_t chunk = count;

  		if (chunk > PAGE_SIZE)
  			chunk = PAGE_SIZE;	/* Just for latency reasons */

  		unwritten = __clear_user(buf, chunk);

  		written += chunk - unwritten;

  		if (unwritten)

  			break;

  		if (signal_pending(current))
  			return written ? written : -ERESTARTSYS;

  		buf += chunk;

  		count -= chunk;

  		cond_resched();
  	}

  	return written ? written : -EFAULT;

  }

  static ssize_t aio_read_zero(struct kiocb *iocb, const struct iovec *iov,
  			     unsigned long nr_segs, loff_t pos)
  {
  	size_t written = 0;
  	unsigned long i;
  	ssize_t ret;
  
  	for (i = 0; i < nr_segs; i++) {
  		ret = read_zero(iocb->ki_filp, iov[i].iov_base, iov[i].iov_len,
  				&pos);
  		if (ret < 0)
  			break;
  		written += ret;
  	}
  
  	return written ? written : -EFAULT;
  }

  static int mmap_zero(struct file *file, struct vm_area_struct *vma)

  {

  #ifndef CONFIG_MMU

  	return -ENOSYS;

  #endif
  	if (vma->vm_flags & VM_SHARED)
  		return shmem_zero_setup(vma);
  	return 0;

  }

  static ssize_t write_full(struct file *file, const char __user *buf,

  			  size_t count, loff_t *ppos)
  {
  	return -ENOSPC;
  }
  
  /*
   * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
   * can fopen() both devices with "a" now.  This was previously impossible.
   * -- SRB.
   */

  static loff_t null_lseek(struct file *file, loff_t offset, int orig)

  {
  	return file->f_pos = 0;
  }
  
  /*
   * The memory devices use the full 32/64 bits of the offset, and so we cannot
   * check against negative addresses: they are ok. The return value is weird,
   * though, in that case (0).
   *
   * also note that seeking relative to the "end of file" isn't supported:
   * it has no meaning, so it returns -EINVAL.
   */

  static loff_t memory_lseek(struct file *file, loff_t offset, int orig)

  {
  	loff_t ret;

  	mutex_lock(&file_inode(file)->i_mutex);

  	switch (orig) {

  	case SEEK_CUR:
  		offset += file->f_pos;

  	case SEEK_SET:
  		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */

  		if (IS_ERR_VALUE((unsigned long long)offset)) {

  			ret = -EOVERFLOW;

  			break;

  		}
  		file->f_pos = offset;
  		ret = file->f_pos;
  		force_successful_syscall_return();
  		break;
  	default:
  		ret = -EINVAL;

  	}

  	mutex_unlock(&file_inode(file)->i_mutex);

  	return ret;
  }

  static int open_port(struct inode *inode, struct file *filp)

  {
  	return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
  }
  
  #define zero_lseek	null_lseek
  #define full_lseek      null_lseek
  #define write_zero	write_null
  #define read_full       read_zero

  #define aio_write_zero	aio_write_null

  #define open_mem	open_port
  #define open_kmem	open_mem

  static const struct file_operations mem_fops = {

  	.llseek		= memory_lseek,
  	.read		= read_mem,
  	.write		= write_mem,
  	.mmap		= mmap_mem,
  	.open		= open_mem,

  	.get_unmapped_area = get_unmapped_area_mem,

  };

  #ifdef CONFIG_DEVKMEM

  static const struct file_operations kmem_fops = {

  	.llseek		= memory_lseek,
  	.read		= read_kmem,
  	.write		= write_kmem,
  	.mmap		= mmap_kmem,
  	.open		= open_kmem,

  	.get_unmapped_area = get_unmapped_area_mem,

  };

  #endif

  static const struct file_operations null_fops = {

  	.llseek		= null_lseek,
  	.read		= read_null,
  	.write		= write_null,

  	.aio_read	= aio_read_null,
  	.aio_write	= aio_write_null,

  	.splice_write	= splice_write_null,

  };

  #ifdef CONFIG_DEVPORT

  static const struct file_operations port_fops = {

  	.llseek		= memory_lseek,
  	.read		= read_port,
  	.write		= write_port,
  	.open		= open_port,
  };
  #endif

  static const struct file_operations zero_fops = {

  	.llseek		= zero_lseek,
  	.read		= read_zero,
  	.write		= write_zero,

  	.aio_read	= aio_read_zero,
  	.aio_write	= aio_write_zero,

  	.mmap		= mmap_zero,
  };

  /*
   * capabilities for /dev/zero
   * - permits private mappings, "copies" are taken of the source of zeros

   * - no writeback happens

   */

  static struct backing_dev_info zero_bdi = {

  	.name		= "char/mem",

  	.capabilities	= BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,

  };

  static const struct file_operations full_fops = {

  	.llseek		= full_lseek,
  	.read		= read_full,
  	.write		= write_full,
  };

  static const struct memdev {
  	const char *name;

  	umode_t mode;

  	const struct file_operations *fops;
  	struct backing_dev_info *dev_info;
  } devlist[] = {

  	 [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },

  #ifdef CONFIG_DEVKMEM

  	 [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },

  #endif

  	 [3] = { "null", 0666, &null_fops, NULL },

  #ifdef CONFIG_DEVPORT

  	 [4] = { "port", 0, &port_fops, NULL },

  #endif

  	 [5] = { "zero", 0666, &zero_fops, &zero_bdi },
  	 [7] = { "full", 0666, &full_fops, NULL },
  	 [8] = { "random", 0666, &random_fops, NULL },
  	 [9] = { "urandom", 0666, &urandom_fops, NULL },

  #ifdef CONFIG_PRINTK

  	[11] = { "kmsg", 0644, &kmsg_fops, NULL },

  #endif

  };
  
  static int memory_open(struct inode *inode, struct file *filp)
  {

  	int minor;
  	const struct memdev *dev;

  	minor = iminor(inode);
  	if (minor >= ARRAY_SIZE(devlist))

  		return -ENXIO;

  	dev = &devlist[minor];
  	if (!dev->fops)

  		return -ENXIO;

  	filp->f_op = dev->fops;
  	if (dev->dev_info)
  		filp->f_mapping->backing_dev_info = dev->dev_info;

  	/* Is /dev/mem or /dev/kmem ? */
  	if (dev->dev_info == &directly_mappable_cdev_bdi)
  		filp->f_mode |= FMODE_UNSIGNED_OFFSET;

  	if (dev->fops->open)

  		return dev->fops->open(inode, filp);
  
  	return 0;

  }

  static const struct file_operations memory_fops = {

  	.open = memory_open,

  	.llseek = noop_llseek,

  };

  static char *mem_devnode(struct device *dev, umode_t *mode)

  {
  	if (mode && devlist[MINOR(dev->devt)].mode)
  		*mode = devlist[MINOR(dev->devt)].mode;
  	return NULL;
  }

  static struct class *mem_class;

  
  static int __init chr_dev_init(void)
  {

  	int minor;

  	int err;
  
  	err = bdi_init(&zero_bdi);
  	if (err)
  		return err;

  	if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))

  		printk("unable to get major %d for memory devs
  ", MEM_MAJOR);

  	mem_class = class_create(THIS_MODULE, "mem");

  	if (IS_ERR(mem_class))
  		return PTR_ERR(mem_class);

  	mem_class->devnode = mem_devnode;

  	for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
  		if (!devlist[minor].name)
  			continue;

  
  		/*

  		 * Create /dev/port?

  		 */
  		if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
  			continue;

  		device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
  			      NULL, devlist[minor].name);
  	}

  	return tty_init();

  }
  
  fs_initcall(chr_dev_init);