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