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);
25
26/* Read separately compressed datablock directly into page cache */
27int 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_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			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		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_CACHE_SIZE;
100	if (bytes) {
101		pageaddr = kmap_atomic(page[pages - 1]);
102		memset(pageaddr + bytes, 0, PAGE_CACHE_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			page_cache_release(page[i]);
113	}
114
115	kfree(actor);
116	kfree(page);
117
118	return 0;
119
120mark_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		page_cache_release(page[i]);
131	}
132
133out:
134	kfree(actor);
135	kfree(page);
136	return res;
137}
138
139
140static 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_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
157		int avail = min_t(int, bytes, PAGE_CACHE_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_CACHE_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			page_cache_release(page[n]);
171	}
172
173out:
174	squashfs_cache_put(buffer);
175	return res;
176}
177