Quellcode-Bibliothek page_actor.c   Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2013
 * Phillip Lougher <phillip@squashfs.org.uk>
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include "squashfs_fs_sb.h"
#include "decompressor.h"
#include "page_actor.h"

/*
 * This file contains implementations of page_actor for decompressing into
 * an intermediate buffer, and for decompressing directly into the
 * page cache.
 *
 * Calling code should avoid sleeping between calls to squashfs_first_page()
 * and squashfs_finish_page().
 */

/* Implementation of page_actor for decompressing into intermediate buffer */
static void *cache_first_page(struct squashfs_page_actor *actor)
{
 actor->next_page = 1;
 return actor->buffer[0];
}

static void *cache_next_page(struct squashfs_page_actor *actor)
{
 if (actor->next_page == actor->pages)
  return NULL;

 return actor->buffer[actor->next_page++];
}

static void cache_finish_page(struct squashfs_page_actor *actor)
{
 /* empty */
}

struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
 int pages, int length)
{
 struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);

 if (actor == NULL)
  return NULL;

 actor->length = length ? : pages * PAGE_SIZE;
 actor->buffer = buffer;
 actor->pages = pages;
 actor->next_page = 0;
 actor->tmp_buffer = NULL;
 actor->squashfs_first_page = cache_first_page;
 actor->squashfs_next_page = cache_next_page;
 actor->squashfs_finish_page = cache_finish_page;
 return actor;
}

/* Implementation of page_actor for decompressing directly into page cache. */
static loff_t page_next_index(struct squashfs_page_actor *actor)
{
 return page_folio(actor->page[actor->next_page])->index;
}

static void *handle_next_page(struct squashfs_page_actor *actor)
{
 int max_pages = (actor->length + PAGE_SIZE - 1) >> PAGE_SHIFT;

 if (actor->returned_pages == max_pages)
  return NULL;

 if ((actor->next_page == actor->pages) ||
   (actor->next_index != page_next_index(actor))) {
  actor->next_index++;
  actor->returned_pages++;
  actor->last_page = NULL;
  return actor->alloc_buffer ? actor->tmp_buffer : ERR_PTR(-ENOMEM);
 }

 actor->next_index++;
 actor->returned_pages++;
 actor->last_page = actor->page[actor->next_page];
 return actor->pageaddr = kmap_local_page(actor->page[actor->next_page++]);
}

static void *direct_first_page(struct squashfs_page_actor *actor)
{
 return handle_next_page(actor);
}

static void *direct_next_page(struct squashfs_page_actor *actor)
{
 if (actor->pageaddr) {
  kunmap_local(actor->pageaddr);
  actor->pageaddr = NULL;
 }

 return handle_next_page(actor);
}

static void direct_finish_page(struct squashfs_page_actor *actor)
{
 if (actor->pageaddr)
  kunmap_local(actor->pageaddr);
}

struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_info *msblk,
 struct page **page, int pages, int length, loff_t start_index)
{
 struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);

 if (actor == NULL)
  return NULL;

 if (msblk->decompressor->alloc_buffer) {
  actor->tmp_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);

  if (actor->tmp_buffer == NULL) {
   kfree(actor);
   return NULL;
  }
 } else
  actor->tmp_buffer = NULL;

 actor->length = length ? : pages * PAGE_SIZE;
 actor->page = page;
 actor->pages = pages;
 actor->next_page = 0;
 actor->returned_pages = 0;
 actor->next_index = start_index >> PAGE_SHIFT;
 actor->pageaddr = NULL;
 actor->last_page = NULL;
 actor->alloc_buffer = msblk->decompressor->alloc_buffer;
 actor->squashfs_first_page = direct_first_page;
 actor->squashfs_next_page = direct_next_page;
 actor->squashfs_finish_page = direct_finish_page;
 return actor;
}