text: #include <linux/ceph/ceph_debug.h>
  
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/file.h>
  #include <linux/namei.h>
  #include <linux/writeback.h>
  
  #include <linux/ceph/libceph.h>
  
  /*
   * build a vector of user pages
   */
  struct page **ceph_get_direct_page_vector(const char __user *data,
  					  int num_pages, bool write_page)
  {
  	struct page **pages;
  	int got = 0;
  	int rc = 0;
  
  	pages = kmalloc(sizeof(*pages) * num_pages, GFP_NOFS);
  	if (!pages)
  		return ERR_PTR(-ENOMEM);
  
  	down_read(&current->mm->mmap_sem);
  	while (got < num_pages) {
  		rc = get_user_pages(current, current->mm,
  		    (unsigned long)data + ((unsigned long)got * PAGE_SIZE),
  		    num_pages - got, write_page, 0, pages + got, NULL);
  		if (rc < 0)
  			break;
  		BUG_ON(rc == 0);
  		got += rc;
  	}
  	up_read(&current->mm->mmap_sem);
  	if (rc < 0)
  		goto fail;
  	return pages;
  
  fail:
  	ceph_put_page_vector(pages, got, false);
  	return ERR_PTR(rc);
  }
  EXPORT_SYMBOL(ceph_get_direct_page_vector);
  
  void ceph_put_page_vector(struct page **pages, int num_pages, bool dirty)
  {
  	int i;
  
  	for (i = 0; i < num_pages; i++) {
  		if (dirty)
  			set_page_dirty_lock(pages[i]);
  		put_page(pages[i]);
  	}
  	kfree(pages);
  }
  EXPORT_SYMBOL(ceph_put_page_vector);
  
  void ceph_release_page_vector(struct page **pages, int num_pages)
  {
  	int i;
  
  	for (i = 0; i < num_pages; i++)
  		__free_pages(pages[i], 0);
  	kfree(pages);
  }
  EXPORT_SYMBOL(ceph_release_page_vector);
  
  /*
   * allocate a vector new pages
   */
  struct page **ceph_alloc_page_vector(int num_pages, gfp_t flags)
  {
  	struct page **pages;
  	int i;
  
  	pages = kmalloc(sizeof(*pages) * num_pages, flags);
  	if (!pages)
  		return ERR_PTR(-ENOMEM);
  	for (i = 0; i < num_pages; i++) {
  		pages[i] = __page_cache_alloc(flags);
  		if (pages[i] == NULL) {
  			ceph_release_page_vector(pages, i);
  			return ERR_PTR(-ENOMEM);
  		}
  	}
  	return pages;
  }
  EXPORT_SYMBOL(ceph_alloc_page_vector);
  
  /*
   * copy user data into a page vector
   */
  int ceph_copy_user_to_page_vector(struct page **pages,
  					 const char __user *data,
  					 loff_t off, size_t len)
  {
  	int i = 0;
  	int po = off & ~PAGE_CACHE_MASK;
  	int left = len;
  	int l, bad;
  
  	while (left > 0) {
  		l = min_t(int, PAGE_CACHE_SIZE-po, left);
  		bad = copy_from_user(page_address(pages[i]) + po, data, l);
  		if (bad == l)
  			return -EFAULT;
  		data += l - bad;
  		left -= l - bad;
  		po += l - bad;
  		if (po == PAGE_CACHE_SIZE) {
  			po = 0;
  			i++;
  		}
  	}
  	return len;
  }
  EXPORT_SYMBOL(ceph_copy_user_to_page_vector);
  
  int ceph_copy_to_page_vector(struct page **pages,
  				    const char *data,
  				    loff_t off, size_t len)
  {
  	int i = 0;
  	size_t po = off & ~PAGE_CACHE_MASK;
  	size_t left = len;
  	size_t l;
  
  	while (left > 0) {
  		l = min_t(size_t, PAGE_CACHE_SIZE-po, left);
  		memcpy(page_address(pages[i]) + po, data, l);
  		data += l;
  		left -= l;
  		po += l;
  		if (po == PAGE_CACHE_SIZE) {
  			po = 0;
  			i++;
  		}
  	}
  	return len;
  }
  EXPORT_SYMBOL(ceph_copy_to_page_vector);
  
  int ceph_copy_from_page_vector(struct page **pages,
  				    char *data,
  				    loff_t off, size_t len)
  {
  	int i = 0;
  	size_t po = off & ~PAGE_CACHE_MASK;
  	size_t left = len;
  	size_t l;
  
  	while (left > 0) {
  		l = min_t(size_t, PAGE_CACHE_SIZE-po, left);
  		memcpy(data, page_address(pages[i]) + po, l);
  		data += l;
  		left -= l;
  		po += l;
  		if (po == PAGE_CACHE_SIZE) {
  			po = 0;
  			i++;
  		}
  	}
  	return len;
  }
  EXPORT_SYMBOL(ceph_copy_from_page_vector);
  
  /*
   * copy user data from a page vector into a user pointer
   */
  int ceph_copy_page_vector_to_user(struct page **pages,
  					 char __user *data,
  					 loff_t off, size_t len)
  {
  	int i = 0;
  	int po = off & ~PAGE_CACHE_MASK;
  	int left = len;
  	int l, bad;
  
  	while (left > 0) {
  		l = min_t(int, left, PAGE_CACHE_SIZE-po);
  		bad = copy_to_user(data, page_address(pages[i]) + po, l);
  		if (bad == l)
  			return -EFAULT;
  		data += l - bad;
  		left -= l - bad;
  		if (po) {
  			po += l - bad;
  			if (po == PAGE_CACHE_SIZE)
  				po = 0;
  		}
  		i++;
  	}
  	return len;
  }
  EXPORT_SYMBOL(ceph_copy_page_vector_to_user);
  
  /*
   * Zero an extent within a page vector.  Offset is relative to the
   * start of the first page.
   */
  void ceph_zero_page_vector_range(int off, int len, struct page **pages)
  {
  	int i = off >> PAGE_CACHE_SHIFT;
  
  	off &= ~PAGE_CACHE_MASK;
  
  	dout("zero_page_vector_page %u~%u\n", off, len);
  
  	/* leading partial page? */
  	if (off) {
  		int end = min((int)PAGE_CACHE_SIZE, off + len);
  		dout("zeroing %d %p head from %d\n", i, pages[i],
  		     (int)off);
  		zero_user_segment(pages[i], off, end);
  		len -= (end - off);
  		i++;
  	}
  	while (len >= PAGE_CACHE_SIZE) {
  		dout("zeroing %d %p len=%d\n", i, pages[i], len);
  		zero_user_segment(pages[i], 0, PAGE_CACHE_SIZE);
  		len -= PAGE_CACHE_SIZE;
  		i++;
  	}
  	/* trailing partial page? */
  	if (len) {
  		dout("zeroing %d %p tail to %d\n", i, pages[i], (int)len);
  		zero_user_segment(pages[i], 0, len);
  	}
  }
  EXPORT_SYMBOL(ceph_zero_page_vector_range);
  
  