fs/squashfs/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 */
  24 static void *cache_first_page(struct squashfs_page_actor *actor)
  25 {
  26         actor->next_page = 1;
  27         return actor->buffer[0];
  28 }
  29
  30 static 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
  38 static void cache_finish_page(struct squashfs_page_actor *actor)
  39 {
  40         /* empty */
  41 }
  42
  43 struct 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->squashfs_first_page = cache_first_page;
  56         actor->squashfs_next_page = cache_next_page;
  57         actor->squashfs_finish_page = cache_finish_page;
  58         return actor;
  59 }
  60
  61 /* Implementation of page_actor for decompressing directly into page cache. */
  62 static void *handle_next_page(struct squashfs_page_actor *actor)
  63 {
  64         int max_pages = (actor->length + PAGE_SIZE - 1) >> PAGE_SHIFT;
  65
  66         if (actor->returned_pages == max_pages)
  67                 return NULL;
  68
  69         if ((actor->next_page == actor->pages) ||
  70                         (actor->next_index != actor->page[actor->next_page]->index)) {
  71                 if (actor->alloc_buffer) {
  72                         void *tmp_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
  73
  74                         if (tmp_buffer) {
  75                                 actor->tmp_buffer = tmp_buffer;
  76                                 actor->next_index++;
  77                                 actor->returned_pages++;
  78                                 return tmp_buffer;
  79                         }
  80                 }
  81
  82                 actor->next_index++;
  83                 actor->returned_pages++;
  84                 return ERR_PTR(-ENOMEM);
  85         }
  86
  87         actor->next_index++;
  88         actor->returned_pages++;
  89         return actor->pageaddr = kmap_local_page(actor->page[actor->next_page++]);
  90 }
  91
  92 static void *direct_first_page(struct squashfs_page_actor *actor)
  93 {
  94         return handle_next_page(actor);
  95 }
  96
  97 static void *direct_next_page(struct squashfs_page_actor *actor)
  98 {
  99         if (actor->pageaddr)
 100                 kunmap_local(actor->pageaddr);
 101
 102         kfree(actor->tmp_buffer);
 103         actor->pageaddr = actor->tmp_buffer = NULL;
 104
 105         return handle_next_page(actor);
 106 }
 107
 108 static void direct_finish_page(struct squashfs_page_actor *actor)
 109 {
 110         if (actor->pageaddr)
 111                 kunmap_local(actor->pageaddr);
 112
 113         kfree(actor->tmp_buffer);
 114 }
 115
 116 struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_info *msblk,
 117         struct page **page, int pages, int length)
 118 {
 119         struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
 120
 121         if (actor == NULL)
 122                 return NULL;
 123
 124         actor->length = length ? : pages * PAGE_SIZE;
 125         actor->page = page;
 126         actor->pages = pages;
 127         actor->next_page = 0;
 128         actor->returned_pages = 0;
 129         actor->next_index = page[0]->index & ~((1 << (msblk->block_log - PAGE_SHIFT)) - 1);
 130         actor->pageaddr = NULL;
 131         actor->tmp_buffer = NULL;
 132         actor->alloc_buffer = msblk->decompressor->alloc_buffer;
 133         actor->squashfs_first_page = direct_first_page;
 134         actor->squashfs_next_page = direct_next_page;
 135         actor->squashfs_finish_page = direct_finish_page;
 136         return actor;
 137 }