text: /*
   * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   * Licensed under the GPL
   */
  
  #include <linux/err.h>
  #include <linux/highmem.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <asm/current.h>
  #include <asm/page.h>
  #include <asm/pgtable.h>
  #include "kern_util.h"
  #include "os.h"
  
  pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  
  	if (mm == NULL)
  		return NULL;
  
  	pgd = pgd_offset(mm, addr);
  	if (!pgd_present(*pgd))
  		return NULL;
  
  	pud = pud_offset(pgd, addr);
  	if (!pud_present(*pud))
  		return NULL;
  
  	pmd = pmd_offset(pud, addr);
  	if (!pmd_present(*pmd))
  		return NULL;
  
  	return pte_offset_kernel(pmd, addr);
  }
  
  static pte_t *maybe_map(unsigned long virt, int is_write)
  {
  	pte_t *pte = virt_to_pte(current->mm, virt);
  	int err, dummy_code;
  
  	if ((pte == NULL) || !pte_present(*pte) ||
  	    (is_write && !pte_write(*pte))) {
  		err = handle_page_fault(virt, 0, is_write, 1, &dummy_code);
  		if (err)
  			return NULL;
  		pte = virt_to_pte(current->mm, virt);
  	}
  	if (!pte_present(*pte))
  		pte = NULL;
  
  	return pte;
  }
  
  static int do_op_one_page(unsigned long addr, int len, int is_write,
  		 int (*op)(unsigned long addr, int len, void *arg), void *arg)
  {
  	jmp_buf buf;
  	struct page *page;
  	pte_t *pte;
  	int n, faulted;
  
  	pte = maybe_map(addr, is_write);
  	if (pte == NULL)
  		return -1;
  
  	page = pte_page(*pte);
  	addr = (unsigned long) kmap_atomic(page) +
  		(addr & ~PAGE_MASK);
  
  	current->thread.fault_catcher = &buf;
  
  	faulted = UML_SETJMP(&buf);
  	if (faulted == 0)
  		n = (*op)(addr, len, arg);
  	else
  		n = -1;
  
  	current->thread.fault_catcher = NULL;
  
  	kunmap_atomic((void *)addr);
  
  	return n;
  }
  
  static int buffer_op(unsigned long addr, int len, int is_write,
  		     int (*op)(unsigned long, int, void *), void *arg)
  {
  	int size, remain, n;
  
  	size = min(PAGE_ALIGN(addr) - addr, (unsigned long) len);
  	remain = len;
  
  	n = do_op_one_page(addr, size, is_write, op, arg);
  	if (n != 0) {
  		remain = (n < 0 ? remain : 0);
  		goto out;
  	}
  
  	addr += size;
  	remain -= size;
  	if (remain == 0)
  		goto out;
  
  	while (addr < ((addr + remain) & PAGE_MASK)) {
  		n = do_op_one_page(addr, PAGE_SIZE, is_write, op, arg);
  		if (n != 0) {
  			remain = (n < 0 ? remain : 0);
  			goto out;
  		}
  
  		addr += PAGE_SIZE;
  		remain -= PAGE_SIZE;
  	}
  	if (remain == 0)
  		goto out;
  
  	n = do_op_one_page(addr, remain, is_write, op, arg);
  	if (n != 0) {
  		remain = (n < 0 ? remain : 0);
  		goto out;
  	}
  
  	return 0;
   out:
  	return remain;
  }
  
  static int copy_chunk_from_user(unsigned long from, int len, void *arg)
  {
  	unsigned long *to_ptr = arg, to = *to_ptr;
  
  	memcpy((void *) to, (void *) from, len);
  	*to_ptr += len;
  	return 0;
  }
  
  int copy_from_user(void *to, const void __user *from, int n)
  {
  	if (segment_eq(get_fs(), KERNEL_DS)) {
  		memcpy(to, (__force void*)from, n);
  		return 0;
  	}
  
  	return access_ok(VERIFY_READ, from, n) ?
  	       buffer_op((unsigned long) from, n, 0, copy_chunk_from_user, &to):
  	       n;
  }
  EXPORT_SYMBOL(copy_from_user);
  
  static int copy_chunk_to_user(unsigned long to, int len, void *arg)
  {
  	unsigned long *from_ptr = arg, from = *from_ptr;
  
  	memcpy((void *) to, (void *) from, len);
  	*from_ptr += len;
  	return 0;
  }
  
  int copy_to_user(void __user *to, const void *from, int n)
  {
  	if (segment_eq(get_fs(), KERNEL_DS)) {
  		memcpy((__force void *) to, from, n);
  		return 0;
  	}
  
  	return access_ok(VERIFY_WRITE, to, n) ?
  	       buffer_op((unsigned long) to, n, 1, copy_chunk_to_user, &from) :
  	       n;
  }
  EXPORT_SYMBOL(copy_to_user);
  
  static int strncpy_chunk_from_user(unsigned long from, int len, void *arg)
  {
  	char **to_ptr = arg, *to = *to_ptr;
  	int n;
  
  	strncpy(to, (void *) from, len);
  	n = strnlen(to, len);
  	*to_ptr += n;
  
  	if (n < len)
  	        return 1;
  	return 0;
  }
  
  int strncpy_from_user(char *dst, const char __user *src, int count)
  {
  	int n;
  	char *ptr = dst;
  
  	if (segment_eq(get_fs(), KERNEL_DS)) {
  		strncpy(dst, (__force void *) src, count);
  		return strnlen(dst, count);
  	}
  
  	if (!access_ok(VERIFY_READ, src, 1))
  		return -EFAULT;
  
  	n = buffer_op((unsigned long) src, count, 0, strncpy_chunk_from_user,
  		      &ptr);
  	if (n != 0)
  		return -EFAULT;
  	return strnlen(dst, count);
  }
  EXPORT_SYMBOL(strncpy_from_user);
  
  static int clear_chunk(unsigned long addr, int len, void *unused)
  {
  	memset((void *) addr, 0, len);
  	return 0;
  }
  
  int __clear_user(void __user *mem, int len)
  {
  	return buffer_op((unsigned long) mem, len, 1, clear_chunk, NULL);
  }
  
  int clear_user(void __user *mem, int len)
  {
  	if (segment_eq(get_fs(), KERNEL_DS)) {
  		memset((__force void*)mem, 0, len);
  		return 0;
  	}
  
  	return access_ok(VERIFY_WRITE, mem, len) ?
  	       buffer_op((unsigned long) mem, len, 1, clear_chunk, NULL) : len;
  }
  EXPORT_SYMBOL(clear_user);
  
  static int strnlen_chunk(unsigned long str, int len, void *arg)
  {
  	int *len_ptr = arg, n;
  
  	n = strnlen((void *) str, len);
  	*len_ptr += n;
  
  	if (n < len)
  		return 1;
  	return 0;
  }
  
  int strnlen_user(const void __user *str, int len)
  {
  	int count = 0, n;
  
  	if (segment_eq(get_fs(), KERNEL_DS))
  		return strnlen((__force char*)str, len) + 1;
  
  	n = buffer_op((unsigned long) str, len, 0, strnlen_chunk, &count);
  	if (n == 0)
  		return count + 1;
  	return -EFAULT;
  }
  EXPORT_SYMBOL(strnlen_user);
  