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Linux/fs/squashfs/file_direct.c

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  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_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 
120 mark_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 
133 out:
134         kfree(actor);
135         kfree(page);
136         return res;
137 }
138 
139 
140 static 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 
173 out:
174         squashfs_cache_put(buffer);
175         return res;
176 }
177 

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