page_actor.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (c) 2013
  4 * Phillip Lougher <phillip@squashfs.org.uk>
  5 */
  6
  7#include <linux/kernel.h>
  8#include <linux/slab.h>
  9#include <linux/pagemap.h>
 10#include "squashfs_fs_sb.h"
 11#include "decompressor.h"
 12#include "page_actor.h"
 13
 14/*
 15 * This file contains implementations of page_actor for decompressing into
 16 * an intermediate buffer, and for decompressing directly into the
 17 * page cache.
 18 *
 19 * Calling code should avoid sleeping between calls to squashfs_first_page()
 20 * and squashfs_finish_page().
 21 */
 22
 23/* Implementation of page_actor for decompressing into intermediate buffer */
 24static void *cache_first_page(struct squashfs_page_actor *actor)
 25{
 26	actor->next_page = 1;
 27	return actor->buffer[0];
 28}
 29
 30static void *cache_next_page(struct squashfs_page_actor *actor)
 31{
 32	if (actor->next_page == actor->pages)
 33		return NULL;
 34
 35	return actor->buffer[actor->next_page++];
 36}
 37
 38static void cache_finish_page(struct squashfs_page_actor *actor)
 39{
 40	/* empty */
 41}
 42
 43struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
 44	int pages, int length)
 45{
 46	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
 47
 48	if (actor == NULL)
 49		return NULL;
 50
 51	actor->length = length ? : pages * PAGE_SIZE;
 52	actor->buffer = buffer;
 53	actor->pages = pages;
 54	actor->next_page = 0;
 55	actor->tmp_buffer = NULL;
 56	actor->squashfs_first_page = cache_first_page;
 57	actor->squashfs_next_page = cache_next_page;
 58	actor->squashfs_finish_page = cache_finish_page;
 59	return actor;
 60}
 61
 62/* Implementation of page_actor for decompressing directly into page cache. */
 63static loff_t page_next_index(struct squashfs_page_actor *actor)
 64{
 65	return page_folio(actor->page[actor->next_page])->index;
 66}
 67
 68static void *handle_next_page(struct squashfs_page_actor *actor)
 69{
 70	int max_pages = (actor->length + PAGE_SIZE - 1) >> PAGE_SHIFT;
 71
 72	if (actor->returned_pages == max_pages)
 73		return NULL;
 74
 75	if ((actor->next_page == actor->pages) ||
 76			(actor->next_index != page_next_index(actor))) {
 77		actor->next_index++;
 78		actor->returned_pages++;
 79		actor->last_page = NULL;
 80		return actor->alloc_buffer ? actor->tmp_buffer : ERR_PTR(-ENOMEM);
 81	}
 82
 83	actor->next_index++;
 84	actor->returned_pages++;
 85	actor->last_page = actor->page[actor->next_page];
 86	return actor->pageaddr = kmap_local_page(actor->page[actor->next_page++]);
 87}
 88
 89static void *direct_first_page(struct squashfs_page_actor *actor)
 90{
 91	return handle_next_page(actor);
 92}
 93
 94static void *direct_next_page(struct squashfs_page_actor *actor)
 95{
 96	if (actor->pageaddr) {
 97		kunmap_local(actor->pageaddr);
 98		actor->pageaddr = NULL;
 99	}
100
101	return handle_next_page(actor);
102}
103
104static void direct_finish_page(struct squashfs_page_actor *actor)
105{
106	if (actor->pageaddr)
107		kunmap_local(actor->pageaddr);
108}
109
110struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_info *msblk,
111	struct page **page, int pages, int length, loff_t start_index)
112{
113	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
114
115	if (actor == NULL)
116		return NULL;
117
118	if (msblk->decompressor->alloc_buffer) {
119		actor->tmp_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
120
121		if (actor->tmp_buffer == NULL) {
122			kfree(actor);
123			return NULL;
124		}
125	} else
126		actor->tmp_buffer = NULL;
127
128	actor->length = length ? : pages * PAGE_SIZE;
129	actor->page = page;
130	actor->pages = pages;
131	actor->next_page = 0;
132	actor->returned_pages = 0;
133	actor->next_index = start_index >> PAGE_SHIFT;
134	actor->pageaddr = NULL;
135	actor->last_page = NULL;
136	actor->alloc_buffer = msblk->decompressor->alloc_buffer;
137	actor->squashfs_first_page = direct_first_page;
138	actor->squashfs_next_page = direct_next_page;
139	actor->squashfs_finish_page = direct_finish_page;
140	return actor;
141}