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, int bytes);
  25
  26 /* Read separately compressed datablock directly into page cache */
  27 int 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
 126 mark_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
 139 out:
 140         kfree(actor);
 141         kfree(page);
 142         return res;
 143 }
 144
 145
 146 static 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
 173 out:
 174         squashfs_cache_put(buffer);
 175         return res;
 176 }