#include <linux/mm.h>

  #include <linux/slab.h>
  #include <linux/string.h>

  #include <linux/compiler.h>

  #include <linux/export.h>

  #include <linux/err.h>

  #include <linux/sched.h>

  #include <linux/sched/mm.h>

  #include <linux/sched/task_stack.h>

  #include <linux/security.h>

  #include <linux/swap.h>

  #include <linux/swapops.h>

  #include <linux/mman.h>
  #include <linux/hugetlb.h>

  #include <linux/vmalloc.h>

  #include <linux/userfaultfd_k.h>

  #include <asm/sections.h>

  #include <linux/uaccess.h>

  #include "internal.h"

  static inline int is_kernel_rodata(unsigned long addr)
  {
  	return addr >= (unsigned long)__start_rodata &&
  		addr < (unsigned long)__end_rodata;
  }
  
  /**
   * kfree_const - conditionally free memory
   * @x: pointer to the memory
   *
   * Function calls kfree only if @x is not in .rodata section.
   */
  void kfree_const(const void *x)
  {
  	if (!is_kernel_rodata((unsigned long)x))
  		kfree(x);
  }
  EXPORT_SYMBOL(kfree_const);

  /**

   * kstrdup - allocate space for and copy an existing string

   * @s: the string to duplicate
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory
   */
  char *kstrdup(const char *s, gfp_t gfp)
  {
  	size_t len;
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	len = strlen(s) + 1;

  	buf = kmalloc_track_caller(len, gfp);

  	if (buf)
  		memcpy(buf, s, len);
  	return buf;
  }
  EXPORT_SYMBOL(kstrdup);

  /**

   * kstrdup_const - conditionally duplicate an existing const string
   * @s: the string to duplicate
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory
   *
   * Function returns source string if it is in .rodata section otherwise it
   * fallbacks to kstrdup.
   * Strings allocated by kstrdup_const should be freed by kfree_const.
   */
  const char *kstrdup_const(const char *s, gfp_t gfp)
  {
  	if (is_kernel_rodata((unsigned long)s))
  		return s;
  
  	return kstrdup(s, gfp);
  }
  EXPORT_SYMBOL(kstrdup_const);
  
  /**

   * kstrndup - allocate space for and copy an existing string
   * @s: the string to duplicate
   * @max: read at most @max chars from @s
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory

   *
   * Note: Use kmemdup_nul() instead if the size is known exactly.

   */
  char *kstrndup(const char *s, size_t max, gfp_t gfp)
  {
  	size_t len;
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	len = strnlen(s, max);
  	buf = kmalloc_track_caller(len+1, gfp);
  	if (buf) {
  		memcpy(buf, s, len);
  		buf[len] = '\0';
  	}
  	return buf;
  }
  EXPORT_SYMBOL(kstrndup);
  
  /**

   * kmemdup - duplicate region of memory
   *
   * @src: memory region to duplicate
   * @len: memory region length
   * @gfp: GFP mask to use
   */
  void *kmemdup(const void *src, size_t len, gfp_t gfp)
  {
  	void *p;

  	p = kmalloc_track_caller(len, gfp);

  	if (p)
  		memcpy(p, src, len);
  	return p;
  }
  EXPORT_SYMBOL(kmemdup);

  /**

   * kmemdup_nul - Create a NUL-terminated string from unterminated data
   * @s: The data to stringify
   * @len: The size of the data
   * @gfp: the GFP mask used in the kmalloc() call when allocating memory
   */
  char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
  {
  	char *buf;
  
  	if (!s)
  		return NULL;
  
  	buf = kmalloc_track_caller(len + 1, gfp);
  	if (buf) {
  		memcpy(buf, s, len);
  		buf[len] = '\0';
  	}
  	return buf;
  }
  EXPORT_SYMBOL(kmemdup_nul);
  
  /**

   * memdup_user - duplicate memory region from user space
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *

   * Returns an ERR_PTR() on failure.  Result is physically
   * contiguous, to be freed by kfree().

   */
  void *memdup_user(const void __user *src, size_t len)
  {
  	void *p;

  	p = kmalloc_track_caller(len, GFP_USER);

  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  
  	return p;
  }
  EXPORT_SYMBOL(memdup_user);

  /**
   * vmemdup_user - duplicate memory region from user space
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *
   * Returns an ERR_PTR() on failure.  Result may be not
   * physically contiguous.  Use kvfree() to free.
   */
  void *vmemdup_user(const void __user *src, size_t len)
  {
  	void *p;
  
  	p = kvmalloc(len, GFP_USER);
  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kvfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  
  	return p;
  }
  EXPORT_SYMBOL(vmemdup_user);

  /**

   * strndup_user - duplicate an existing string from user space

   * @s: The string to duplicate
   * @n: Maximum number of bytes to copy, including the trailing NUL.
   */
  char *strndup_user(const char __user *s, long n)
  {
  	char *p;
  	long length;
  
  	length = strnlen_user(s, n);
  
  	if (!length)
  		return ERR_PTR(-EFAULT);
  
  	if (length > n)
  		return ERR_PTR(-EINVAL);

  	p = memdup_user(s, length);

  	if (IS_ERR(p))
  		return p;

  
  	p[length - 1] = '\0';
  
  	return p;
  }
  EXPORT_SYMBOL(strndup_user);

  /**
   * memdup_user_nul - duplicate memory region from user space and NUL-terminate
   *
   * @src: source address in user space
   * @len: number of bytes to copy
   *
   * Returns an ERR_PTR() on failure.
   */
  void *memdup_user_nul(const void __user *src, size_t len)
  {
  	char *p;
  
  	/*
  	 * Always use GFP_KERNEL, since copy_from_user() can sleep and
  	 * cause pagefault, which makes it pointless to use GFP_NOFS
  	 * or GFP_ATOMIC.
  	 */
  	p = kmalloc_track_caller(len + 1, GFP_KERNEL);
  	if (!p)
  		return ERR_PTR(-ENOMEM);
  
  	if (copy_from_user(p, src, len)) {
  		kfree(p);
  		return ERR_PTR(-EFAULT);
  	}
  	p[len] = '\0';
  
  	return p;
  }
  EXPORT_SYMBOL(memdup_user_nul);

  void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
  		struct vm_area_struct *prev, struct rb_node *rb_parent)
  {
  	struct vm_area_struct *next;
  
  	vma->vm_prev = prev;
  	if (prev) {
  		next = prev->vm_next;
  		prev->vm_next = vma;
  	} else {
  		mm->mmap = vma;
  		if (rb_parent)
  			next = rb_entry(rb_parent,
  					struct vm_area_struct, vm_rb);
  		else
  			next = NULL;
  	}
  	vma->vm_next = next;
  	if (next)
  		next->vm_prev = vma;
  }

  /* Check if the vma is being used as a stack by this task */

  int vma_is_stack_for_current(struct vm_area_struct *vma)

  {

  	struct task_struct * __maybe_unused t = current;

  	return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t));
  }

  #if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)

  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)

  {
  	mm->mmap_base = TASK_UNMAPPED_BASE;
  	mm->get_unmapped_area = arch_get_unmapped_area;

  }
  #endif

  /*
   * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
   * back to the regular GUP.

   * Note a difference with get_user_pages_fast: this always returns the
   * number of pages pinned, 0 if no pages were pinned.
   * If the architecture does not support this function, simply return with no
   * pages pinned.

   */

  int __weak __get_user_pages_fast(unsigned long start,

  				 int nr_pages, int write, struct page **pages)
  {
  	return 0;
  }
  EXPORT_SYMBOL_GPL(__get_user_pages_fast);

  /**
   * get_user_pages_fast() - pin user pages in memory
   * @start:	starting user address
   * @nr_pages:	number of pages from start to pin
   * @write:	whether pages will be written to
   * @pages:	array that receives pointers to the pages pinned.
   *		Should be at least nr_pages long.
   *

   * Returns number of pages pinned. This may be fewer than the number
   * requested. If nr_pages is 0 or negative, returns 0. If no pages
   * were pinned, returns -errno.

   *
   * get_user_pages_fast provides equivalent functionality to get_user_pages,
   * operating on current and current->mm, with force=0 and vma=NULL. However
   * unlike get_user_pages, it must be called without mmap_sem held.
   *
   * get_user_pages_fast may take mmap_sem and page table locks, so no
   * assumptions can be made about lack of locking. get_user_pages_fast is to be
   * implemented in a way that is advantageous (vs get_user_pages()) when the
   * user memory area is already faulted in and present in ptes. However if the
   * pages have to be faulted in, it may turn out to be slightly slower so
   * callers need to carefully consider what to use. On many architectures,
   * get_user_pages_fast simply falls back to get_user_pages.

   */

  int __weak get_user_pages_fast(unsigned long start,

  				int nr_pages, int write, struct page **pages)
  {

  	return get_user_pages_unlocked(start, nr_pages, pages,
  				       write ? FOLL_WRITE : 0);

  }
  EXPORT_SYMBOL_GPL(get_user_pages_fast);

  unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
  	unsigned long len, unsigned long prot,

  	unsigned long flag, unsigned long pgoff)

  {
  	unsigned long ret;
  	struct mm_struct *mm = current->mm;

  	unsigned long populate;

  	LIST_HEAD(uf);

  
  	ret = security_mmap_file(file, prot, flag);
  	if (!ret) {

  		if (down_write_killable(&mm->mmap_sem))
  			return -EINTR;

  		ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,

  				    &populate, &uf);

  		up_write(&mm->mmap_sem);

  		userfaultfd_unmap_complete(mm, &uf);

  		if (populate)
  			mm_populate(ret, populate);

  	}
  	return ret;
  }
  
  unsigned long vm_mmap(struct file *file, unsigned long addr,
  	unsigned long len, unsigned long prot,
  	unsigned long flag, unsigned long offset)
  {
  	if (unlikely(offset + PAGE_ALIGN(len) < offset))
  		return -EINVAL;

  	if (unlikely(offset_in_page(offset)))

  		return -EINVAL;

  	return vm_mmap_pgoff(file, addr, len, prot, flag, offset >> PAGE_SHIFT);

  }
  EXPORT_SYMBOL(vm_mmap);

  /**
   * kvmalloc_node - attempt to allocate physically contiguous memory, but upon
   * failure, fall back to non-contiguous (vmalloc) allocation.
   * @size: size of the request.
   * @flags: gfp mask for the allocation - must be compatible (superset) with GFP_KERNEL.
   * @node: numa node to allocate from
   *
   * Uses kmalloc to get the memory but if the allocation fails then falls back
   * to the vmalloc allocator. Use kvfree for freeing the memory.
   *

   * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported.
   * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is
   * preferable to the vmalloc fallback, due to visible performance drawbacks.

   *

   * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not
   * fall back to vmalloc.

   */
  void *kvmalloc_node(size_t size, gfp_t flags, int node)
  {
  	gfp_t kmalloc_flags = flags;
  	void *ret;
  
  	/*
  	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
  	 * so the given set of flags has to be compatible.
  	 */

  	if ((flags & GFP_KERNEL) != GFP_KERNEL)
  		return kmalloc_node(size, flags, node);

  
  	/*

  	 * We want to attempt a large physically contiguous block first because
  	 * it is less likely to fragment multiple larger blocks and therefore
  	 * contribute to a long term fragmentation less than vmalloc fallback.
  	 * However make sure that larger requests are not too disruptive - no
  	 * OOM killer and no allocation failure warnings as we have a fallback.

  	 */

  	if (size > PAGE_SIZE) {
  		kmalloc_flags |= __GFP_NOWARN;

  		if (!(kmalloc_flags & __GFP_RETRY_MAYFAIL))

  			kmalloc_flags |= __GFP_NORETRY;
  	}

  
  	ret = kmalloc_node(size, kmalloc_flags, node);
  
  	/*
  	 * It doesn't really make sense to fallback to vmalloc for sub page
  	 * requests
  	 */
  	if (ret || size <= PAGE_SIZE)
  		return ret;

  	return __vmalloc_node_flags_caller(size, node, flags,
  			__builtin_return_address(0));

  }
  EXPORT_SYMBOL(kvmalloc_node);

  /**

   * kvfree() - Free memory.
   * @addr: Pointer to allocated memory.

   *

   * kvfree frees memory allocated by any of vmalloc(), kmalloc() or kvmalloc().
   * It is slightly more efficient to use kfree() or vfree() if you are certain
   * that you know which one to use.
   *
   * Context: Any context except NMI.

   */

  void kvfree(const void *addr)
  {
  	if (is_vmalloc_addr(addr))
  		vfree(addr);
  	else
  		kfree(addr);
  }
  EXPORT_SYMBOL(kvfree);

  static inline void *__page_rmapping(struct page *page)
  {
  	unsigned long mapping;
  
  	mapping = (unsigned long)page->mapping;
  	mapping &= ~PAGE_MAPPING_FLAGS;
  
  	return (void *)mapping;
  }
  
  /* Neutral page->mapping pointer to address_space or anon_vma or other */
  void *page_rmapping(struct page *page)
  {
  	page = compound_head(page);
  	return __page_rmapping(page);
  }

  /*
   * Return true if this page is mapped into pagetables.
   * For compound page it returns true if any subpage of compound page is mapped.
   */
  bool page_mapped(struct page *page)
  {
  	int i;
  
  	if (likely(!PageCompound(page)))
  		return atomic_read(&page->_mapcount) >= 0;
  	page = compound_head(page);
  	if (atomic_read(compound_mapcount_ptr(page)) >= 0)
  		return true;
  	if (PageHuge(page))
  		return false;

  	for (i = 0; i < (1 << compound_order(page)); i++) {

  		if (atomic_read(&page[i]._mapcount) >= 0)
  			return true;
  	}
  	return false;
  }
  EXPORT_SYMBOL(page_mapped);

  struct anon_vma *page_anon_vma(struct page *page)
  {
  	unsigned long mapping;
  
  	page = compound_head(page);
  	mapping = (unsigned long)page->mapping;
  	if ((mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
  		return NULL;
  	return __page_rmapping(page);
  }

  struct address_space *page_mapping(struct page *page)
  {

  	struct address_space *mapping;
  
  	page = compound_head(page);

  	/* This happens if someone calls flush_dcache_page on slab page */
  	if (unlikely(PageSlab(page)))
  		return NULL;

  	if (unlikely(PageSwapCache(page))) {
  		swp_entry_t entry;
  
  		entry.val = page_private(page);

  		return swap_address_space(entry);
  	}

  	mapping = page->mapping;

  	if ((unsigned long)mapping & PAGE_MAPPING_ANON)

  		return NULL;

  
  	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);

  }

  EXPORT_SYMBOL(page_mapping);

  /*
   * For file cache pages, return the address_space, otherwise return NULL
   */
  struct address_space *page_mapping_file(struct page *page)
  {
  	if (unlikely(PageSwapCache(page)))
  		return NULL;
  	return page_mapping(page);
  }

  /* Slow path of page_mapcount() for compound pages */
  int __page_mapcount(struct page *page)
  {
  	int ret;
  
  	ret = atomic_read(&page->_mapcount) + 1;

  	/*
  	 * For file THP page->_mapcount contains total number of mapping
  	 * of the page: no need to look into compound_mapcount.
  	 */
  	if (!PageAnon(page) && !PageHuge(page))
  		return ret;

  	page = compound_head(page);
  	ret += atomic_read(compound_mapcount_ptr(page)) + 1;
  	if (PageDoubleMap(page))
  		ret--;
  	return ret;
  }
  EXPORT_SYMBOL_GPL(__page_mapcount);

  int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
  int sysctl_overcommit_ratio __read_mostly = 50;
  unsigned long sysctl_overcommit_kbytes __read_mostly;
  int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
  unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
  unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */

  int overcommit_ratio_handler(struct ctl_table *table, int write,
  			     void __user *buffer, size_t *lenp,
  			     loff_t *ppos)
  {
  	int ret;
  
  	ret = proc_dointvec(table, write, buffer, lenp, ppos);
  	if (ret == 0 && write)
  		sysctl_overcommit_kbytes = 0;
  	return ret;
  }
  
  int overcommit_kbytes_handler(struct ctl_table *table, int write,
  			     void __user *buffer, size_t *lenp,
  			     loff_t *ppos)
  {
  	int ret;
  
  	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  	if (ret == 0 && write)
  		sysctl_overcommit_ratio = 0;
  	return ret;
  }

  /*
   * Committed memory limit enforced when OVERCOMMIT_NEVER policy is used
   */
  unsigned long vm_commit_limit(void)
  {

  	unsigned long allowed;
  
  	if (sysctl_overcommit_kbytes)
  		allowed = sysctl_overcommit_kbytes >> (PAGE_SHIFT - 10);
  	else
  		allowed = ((totalram_pages - hugetlb_total_pages())
  			   * sysctl_overcommit_ratio / 100);
  	allowed += total_swap_pages;
  
  	return allowed;

  }

  /*
   * Make sure vm_committed_as in one cacheline and not cacheline shared with
   * other variables. It can be updated by several CPUs frequently.
   */
  struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
  
  /*
   * The global memory commitment made in the system can be a metric
   * that can be used to drive ballooning decisions when Linux is hosted
   * as a guest. On Hyper-V, the host implements a policy engine for dynamically
   * balancing memory across competing virtual machines that are hosted.
   * Several metrics drive this policy engine including the guest reported
   * memory commitment.
   */
  unsigned long vm_memory_committed(void)
  {
  	return percpu_counter_read_positive(&vm_committed_as);
  }
  EXPORT_SYMBOL_GPL(vm_memory_committed);
  
  /*
   * Check that a process has enough memory to allocate a new virtual
   * mapping. 0 means there is enough memory for the allocation to
   * succeed and -ENOMEM implies there is not.
   *
   * We currently support three overcommit policies, which are set via the

   * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting.rst

   *
   * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
   * Additional code 2002 Jul 20 by Robert Love.
   *
   * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
   *
   * Note this is a helper function intended to be used by LSMs which
   * wish to use this logic.
   */
  int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
  {
  	long free, allowed, reserve;
  
  	VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
  			-(s64)vm_committed_as_batch * num_online_cpus(),
  			"memory commitment underflow");
  
  	vm_acct_memory(pages);
  
  	/*
  	 * Sometimes we want to use more memory than we have
  	 */
  	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
  		return 0;
  
  	if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {

  		free = global_zone_page_state(NR_FREE_PAGES);

  		free += global_node_page_state(NR_FILE_PAGES);

  
  		/*
  		 * shmem pages shouldn't be counted as free in this
  		 * case, they can't be purged, only swapped out, and
  		 * that won't affect the overall amount of available
  		 * memory in the system.
  		 */

  		free -= global_node_page_state(NR_SHMEM);

  
  		free += get_nr_swap_pages();
  
  		/*
  		 * Any slabs which are created with the
  		 * SLAB_RECLAIM_ACCOUNT flag claim to have contents
  		 * which are reclaimable, under pressure.  The dentry
  		 * cache and most inode caches should fall into this
  		 */

  		free += global_node_page_state(NR_SLAB_RECLAIMABLE);

  
  		/*

  		 * Part of the kernel memory, which can be released
  		 * under memory pressure.
  		 */
  		free += global_node_page_state(
  			NR_INDIRECTLY_RECLAIMABLE_BYTES) >> PAGE_SHIFT;
  
  		/*

  		 * Leave reserved pages. The pages are not for anonymous pages.
  		 */
  		if (free <= totalreserve_pages)
  			goto error;
  		else
  			free -= totalreserve_pages;
  
  		/*
  		 * Reserve some for root
  		 */
  		if (!cap_sys_admin)
  			free -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
  
  		if (free > pages)
  			return 0;
  
  		goto error;
  	}
  
  	allowed = vm_commit_limit();
  	/*
  	 * Reserve some for root
  	 */
  	if (!cap_sys_admin)
  		allowed -= sysctl_admin_reserve_kbytes >> (PAGE_SHIFT - 10);
  
  	/*
  	 * Don't let a single process grow so big a user can't recover
  	 */
  	if (mm) {
  		reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);
  		allowed -= min_t(long, mm->total_vm / 32, reserve);
  	}
  
  	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
  		return 0;
  error:
  	vm_unacct_memory(pages);
  
  	return -ENOMEM;
  }

  /**
   * get_cmdline() - copy the cmdline value to a buffer.
   * @task:     the task whose cmdline value to copy.
   * @buffer:   the buffer to copy to.
   * @buflen:   the length of the buffer. Larger cmdline values are truncated
   *            to this length.
   * Returns the size of the cmdline field copied. Note that the copy does
   * not guarantee an ending NULL byte.
   */
  int get_cmdline(struct task_struct *task, char *buffer, int buflen)
  {
  	int res = 0;
  	unsigned int len;
  	struct mm_struct *mm = get_task_mm(task);

  	unsigned long arg_start, arg_end, env_start, env_end;

  	if (!mm)
  		goto out;
  	if (!mm->arg_end)
  		goto out_mm;	/* Shh! No looking before we're done */

  	down_read(&mm->mmap_sem);
  	arg_start = mm->arg_start;
  	arg_end = mm->arg_end;
  	env_start = mm->env_start;
  	env_end = mm->env_end;
  	up_read(&mm->mmap_sem);
  
  	len = arg_end - arg_start;

  
  	if (len > buflen)
  		len = buflen;

  	res = access_process_vm(task, arg_start, buffer, len, FOLL_FORCE);

  
  	/*
  	 * If the nul at the end of args has been overwritten, then
  	 * assume application is using setproctitle(3).
  	 */
  	if (res > 0 && buffer[res-1] != '\0' && len < buflen) {
  		len = strnlen(buffer, res);
  		if (len < res) {
  			res = len;
  		} else {

  			len = env_end - env_start;

  			if (len > buflen - res)
  				len = buflen - res;

  			res += access_process_vm(task, env_start,

  						 buffer+res, len,
  						 FOLL_FORCE);

  			res = strnlen(buffer, res);
  		}
  	}
  out_mm:
  	mmput(mm);
  out:
  	return res;
  }