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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, 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 }
177 

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