fs/squashfs/file_direct.c

   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
  23 static 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 */
  27 int 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_CACHE_SHIFT;
  34         int mask = (1 << (msblk->block_log - PAGE_CACHE_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(sizeof(void *) * pages, 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                         page_cache_release(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                 goto out;
  88         }
  89
  90         /* Decompress directly into the page cache buffers */
  91         res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
  92         if (res < 0)
  93                 goto mark_errored;
  94
  95         /* Last page may have trailing bytes not filled */
  96         bytes = res % PAGE_CACHE_SIZE;
  97         if (bytes) {
  98                 pageaddr = kmap_atomic(page[pages - 1]);
  99                 memset(pageaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
 100                 kunmap_atomic(pageaddr);
 101         }
 102
 103         /* Mark pages as uptodate, unlock and release */
 104         for (i = 0; i < pages; i++) {
 105                 flush_dcache_page(page[i]);
 106                 SetPageUptodate(page[i]);
 107                 unlock_page(page[i]);
 108                 if (page[i] != target_page)
 109                         page_cache_release(page[i]);
 110         }
 111
 112         kfree(actor);
 113         kfree(page);
 114
 115         return 0;
 116
 117 mark_errored:
 118         /* Decompression failed, mark pages as errored.  Target_page is
 119          * dealt with by the caller
 120          */
 121         for (i = 0; i < pages; i++) {
 122                 if (page[i] == target_page)
 123                         continue;
 124                 flush_dcache_page(page[i]);
 125                 SetPageError(page[i]);
 126                 unlock_page(page[i]);
 127                 page_cache_release(page[i]);
 128         }
 129
 130 out:
 131         kfree(actor);
 132         kfree(page);
 133         return res;
 134 }
 135
 136
 137 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
 138         int pages, struct page **page)
 139 {
 140         struct inode *i = target_page->mapping->host;
 141         struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
 142                                                  block, bsize);
 143         int bytes = buffer->length, res = buffer->error, n, offset = 0;
 144         void *pageaddr;
 145
 146         if (res) {
 147                 ERROR("Unable to read page, block %llx, size %x\n", block,
 148                         bsize);
 149                 goto out;
 150         }
 151
 152         for (n = 0; n < pages && bytes > 0; n++,
 153                         bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
 154                 int avail = min_t(int, bytes, PAGE_CACHE_SIZE);
 155
 156                 if (page[n] == NULL)
 157                         continue;
 158
 159                 pageaddr = kmap_atomic(page[n]);
 160                 squashfs_copy_data(pageaddr, buffer, offset, avail);
 161                 memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
 162                 kunmap_atomic(pageaddr);
 163                 flush_dcache_page(page[n]);
 164                 SetPageUptodate(page[n]);
 165                 unlock_page(page[n]);
 166                 if (page[n] != target_page)
 167                         page_cache_release(page[n]);
 168         }
 169
 170 out:
 171         squashfs_cache_put(buffer);
 172         return res;
 173 }