LXR linux/fs/squashfs/file

   1/*
   2 * Copyright (c) 2013
   3 * Phillip Lougher <phillip@squashfs.org.uk>
   4 *
   5 * This work is licensed under the terms of the GNU GPL, version 2. See
   6 * the COPYING file in the top-level directory.
   7 */
   8
   9#include <linux/fs.h>
  10#include <linux/vfs.h>
  11#include <linux/kernel.h>
  12#include <linux/slab.h>
  13#include <linux/string.h>
  14#include <linux/pagemap.h>
  15#include <linux/mutex.h>
  16
  17#include "squashfs_fs.h"
  18#include "squashfs_fs_sb.h"
  19#include "squashfs_fs_i.h"
  20#include "squashfs.h"
  21#include "page_actor.h"
  22
  23static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
  24        int pages, struct page **page);
  25
  26/* Read separately compressed datablock directly into page cache */
  27int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
  28
  29{
  30        struct inode *inode = target_page->mapping->host;
  31        struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
  32
  33        int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
  34        int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
  35        int start_index = target_page->index & ~mask;
  36        int end_index = start_index | mask;
  37        int i, n, pages, missing_pages, bytes, res = -ENOMEM;
  38        struct page **page;
  39        struct squashfs_page_actor *actor;
  40        void *pageaddr;
  41
  42        if (end_index > file_end)
  43                end_index = file_end;
  44
  45        pages = end_index - start_index + 1;
  46
  47        page = kmalloc_array(pages, sizeof(void *), GFP_KERNEL);
  48        if (page == NULL)
  49                return res;
  50
  51        /*
  52         * Create a "page actor" which will kmap and kunmap the
  53         * page cache pages appropriately within the decompressor
  54         */
  55        actor = squashfs_page_actor_init_special(page, pages, 0);
  56        if (actor == NULL)
  57                goto out;
  58
  59        /* Try to grab all the pages covered by the Squashfs block */
  60        for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
  61                page[i] = (n == target_page->index) ? target_page :
  62                        grab_cache_page_nowait(target_page->mapping, n);
  63
  64                if (page[i] == NULL) {
  65                        missing_pages++;
  66                        continue;
  67                }
  68
  69                if (PageUptodate(page[i])) {
  70                        unlock_page(page[i]);
  71                        put_page(page[i]);
  72                        page[i] = NULL;
  73                        missing_pages++;
  74                }
  75        }
  76
  77        if (missing_pages) {
  78                /*
  79                 * Couldn't get one or more pages, this page has either
  80                 * been VM reclaimed, but others are still in the page cache
  81                 * and uptodate, or we're racing with another thread in
  82                 * squashfs_readpage also trying to grab them.  Fall back to
  83                 * using an intermediate buffer.
  84                 */
  85                res = squashfs_read_cache(target_page, block, bsize, pages,
  86                                                                page);
  87                if (res < 0)
  88                        goto mark_errored;
  89
  90                goto out;
  91        }
  92
  93        /* Decompress directly into the page cache buffers */
  94        res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
  95        if (res < 0)
  96                goto mark_errored;
  97
  98        /* Last page may have trailing bytes not filled */
  99        bytes = res % PAGE_SIZE;
 100        if (bytes) {
 101                pageaddr = kmap_atomic(page[pages - 1]);
 102                memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
 103                kunmap_atomic(pageaddr);
 104        }
 105
 106        /* Mark pages as uptodate, unlock and release */
 107        for (i = 0; i < pages; i++) {
 108                flush_dcache_page(page[i]);
 109                SetPageUptodate(page[i]);
 110                unlock_page(page[i]);
 111                if (page[i] != target_page)
 112                        put_page(page[i]);
 113        }
 114
 115        kfree(actor);
 116        kfree(page);
 117
 118        return 0;
 119
 120mark_errored:
 121        /* Decompression failed, mark pages as errored.  Target_page is
 122         * dealt with by the caller
 123         */
 124        for (i = 0; i < pages; i++) {
 125                if (page[i] == NULL || page[i] == target_page)
 126                        continue;
 127                flush_dcache_page(page[i]);
 128                SetPageError(page[i]);
 129                unlock_page(page[i]);
 130                put_page(page[i]);
 131        }
 132
 133out:
 134        kfree(actor);
 135        kfree(page);
 136        return res;
 137}
 138
 139
 140static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
 141        int pages, struct page **page)
 142{
 143        struct inode *i = target_page->mapping->host;
 144        struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
 145                                                 block, bsize);
 146        int bytes = buffer->length, res = buffer->error, n, offset = 0;
 147        void *pageaddr;
 148
 149        if (res) {
 150                ERROR("Unable to read page, block %llx, size %x\n", block,
 151                        bsize);
 152                goto out;
 153        }
 154
 155        for (n = 0; n < pages && bytes > 0; n++,
 156                        bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
 157                int avail = min_t(int, bytes, PAGE_SIZE);
 158
 159                if (page[n] == NULL)
 160                        continue;
 161
 162                pageaddr = kmap_atomic(page[n]);
 163                squashfs_copy_data(pageaddr, buffer, offset, avail);
 164                memset(pageaddr + avail, 0, PAGE_SIZE - avail);
 165                kunmap_atomic(pageaddr);
 166                flush_dcache_page(page[n]);
 167                SetPageUptodate(page[n]);
 168                unlock_page(page[n]);
 169                if (page[n] != target_page)
 170                        put_page(page[n]);
 171        }
 172
 173out:
 174        squashfs_cache_put(buffer);
 175        return res;
 176}
 177