// SPDX-License-Identifier: GPL-2.0

  #include <linux/module.h>

  #include <linux/gfp.h>

  #include <linux/slab.h>

  #include <linux/pagemap.h>
  #include <linux/highmem.h>

  #include <linux/ceph/pagelist.h>

  static void ceph_pagelist_unmap_tail(struct ceph_pagelist *pl)
  {

  	if (pl->mapped_tail) {
  		struct page *page = list_entry(pl->head.prev, struct page, lru);
  		kunmap(page);
  		pl->mapped_tail = NULL;
  	}

  }

  void ceph_pagelist_release(struct ceph_pagelist *pl)

  {

  	if (!refcount_dec_and_test(&pl->refcnt))

  		return;

  	ceph_pagelist_unmap_tail(pl);

  	while (!list_empty(&pl->head)) {
  		struct page *page = list_first_entry(&pl->head, struct page,
  						     lru);
  		list_del(&page->lru);
  		__free_page(page);
  	}

  	ceph_pagelist_free_reserve(pl);

  	kfree(pl);

  }

  EXPORT_SYMBOL(ceph_pagelist_release);

  
  static int ceph_pagelist_addpage(struct ceph_pagelist *pl)
  {

  	struct page *page;
  
  	if (!pl->num_pages_free) {
  		page = __page_cache_alloc(GFP_NOFS);
  	} else {
  		page = list_first_entry(&pl->free_list, struct page, lru);
  		list_del(&page->lru);

  		--pl->num_pages_free;

  	}

  	if (!page)
  		return -ENOMEM;
  	pl->room += PAGE_SIZE;

  	ceph_pagelist_unmap_tail(pl);

  	list_add_tail(&page->lru, &pl->head);

  	pl->mapped_tail = kmap(page);
  	return 0;
  }

  int ceph_pagelist_append(struct ceph_pagelist *pl, const void *buf, size_t len)

  {
  	while (pl->room < len) {
  		size_t bit = pl->room;
  		int ret;

  		memcpy(pl->mapped_tail + (pl->length & ~PAGE_MASK),

  		       buf, bit);
  		pl->length += bit;
  		pl->room -= bit;
  		buf += bit;
  		len -= bit;
  		ret = ceph_pagelist_addpage(pl);
  		if (ret)
  			return ret;
  	}

  	memcpy(pl->mapped_tail + (pl->length & ~PAGE_MASK), buf, len);

  	pl->length += len;
  	pl->room -= len;
  	return 0;
  }

  EXPORT_SYMBOL(ceph_pagelist_append);

  /* Allocate enough pages for a pagelist to append the given amount

   * of data without without allocating.
   * Returns: 0 on success, -ENOMEM on error.
   */
  int ceph_pagelist_reserve(struct ceph_pagelist *pl, size_t space)
  {
  	if (space <= pl->room)
  		return 0;
  	space -= pl->room;
  	space = (space + PAGE_SIZE - 1) >> PAGE_SHIFT;   /* conv to num pages */
  
  	while (space > pl->num_pages_free) {
  		struct page *page = __page_cache_alloc(GFP_NOFS);
  		if (!page)
  			return -ENOMEM;
  		list_add_tail(&page->lru, &pl->free_list);
  		++pl->num_pages_free;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(ceph_pagelist_reserve);

  /* Free any pages that have been preallocated. */

  int ceph_pagelist_free_reserve(struct ceph_pagelist *pl)
  {
  	while (!list_empty(&pl->free_list)) {
  		struct page *page = list_first_entry(&pl->free_list,
  						     struct page, lru);
  		list_del(&page->lru);
  		__free_page(page);
  		--pl->num_pages_free;
  	}
  	BUG_ON(pl->num_pages_free);
  	return 0;
  }
  EXPORT_SYMBOL(ceph_pagelist_free_reserve);

  /* Create a truncation point. */

  void ceph_pagelist_set_cursor(struct ceph_pagelist *pl,
  			      struct ceph_pagelist_cursor *c)
  {
  	c->pl = pl;
  	c->page_lru = pl->head.prev;
  	c->room = pl->room;
  }
  EXPORT_SYMBOL(ceph_pagelist_set_cursor);

  /* Truncate a pagelist to the given point. Move extra pages to reserve.

   * This won't sleep.
   * Returns: 0 on success,
   *          -EINVAL if the pagelist doesn't match the trunc point pagelist
   */
  int ceph_pagelist_truncate(struct ceph_pagelist *pl,
  			   struct ceph_pagelist_cursor *c)
  {
  	struct page *page;
  
  	if (pl != c->pl)
  		return -EINVAL;
  	ceph_pagelist_unmap_tail(pl);
  	while (pl->head.prev != c->page_lru) {
  		page = list_entry(pl->head.prev, struct page, lru);

  		/* move from pagelist to reserve */
  		list_move_tail(&page->lru, &pl->free_list);

  		++pl->num_pages_free;
  	}
  	pl->room = c->room;
  	if (!list_empty(&pl->head)) {
  		page = list_entry(pl->head.prev, struct page, lru);
  		pl->mapped_tail = kmap(page);
  	}
  	return 0;
  }
  EXPORT_SYMBOL(ceph_pagelist_truncate);