1/*
2 * linux/fs/ext4/readpage.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 * Copyright (C) 2015, Google, Inc.
6 *
7 * This was originally taken from fs/mpage.c
8 *
9 * The intent is the ext4_mpage_readpages() function here is intended
10 * to replace mpage_readpages() in the general case, not just for
11 * encrypted files.  It has some limitations (see below), where it
12 * will fall back to read_block_full_page(), but these limitations
13 * should only be hit when page_size != block_size.
14 *
15 * This will allow us to attach a callback function to support ext4
16 * encryption.
17 *
18 * If anything unusual happens, such as:
19 *
20 * - encountering a page which has buffers
21 * - encountering a page which has a non-hole after a hole
22 * - encountering a page with non-contiguous blocks
23 *
24 * then this code just gives up and calls the buffer_head-based read function.
25 * It does handle a page which has holes at the end - that is a common case:
26 * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
27 *
28 */
29
30#include <linux/kernel.h>
31#include <linux/export.h>
32#include <linux/mm.h>
33#include <linux/kdev_t.h>
34#include <linux/gfp.h>
35#include <linux/bio.h>
36#include <linux/fs.h>
37#include <linux/buffer_head.h>
38#include <linux/blkdev.h>
39#include <linux/highmem.h>
40#include <linux/prefetch.h>
41#include <linux/mpage.h>
42#include <linux/writeback.h>
43#include <linux/backing-dev.h>
44#include <linux/pagevec.h>
45#include <linux/cleancache.h>
46
47#include "ext4.h"
48
49/*
50 * Call ext4_decrypt on every single page, reusing the encryption
51 * context.
52 */
53static void completion_pages(struct work_struct *work)
54{
55#ifdef CONFIG_EXT4_FS_ENCRYPTION
56	struct ext4_crypto_ctx *ctx =
57		container_of(work, struct ext4_crypto_ctx, work);
58	struct bio	*bio	= ctx->bio;
59	struct bio_vec	*bv;
60	int		i;
61
62	bio_for_each_segment_all(bv, bio, i) {
63		struct page *page = bv->bv_page;
64
65		int ret = ext4_decrypt(ctx, page);
66		if (ret) {
67			WARN_ON_ONCE(1);
68			SetPageError(page);
69		} else
70			SetPageUptodate(page);
71		unlock_page(page);
72	}
73	ext4_release_crypto_ctx(ctx);
74	bio_put(bio);
75#else
76	BUG();
77#endif
78}
79
80static inline bool ext4_bio_encrypted(struct bio *bio)
81{
82#ifdef CONFIG_EXT4_FS_ENCRYPTION
83	return unlikely(bio->bi_private != NULL);
84#else
85	return false;
86#endif
87}
88
89/*
90 * I/O completion handler for multipage BIOs.
91 *
92 * The mpage code never puts partial pages into a BIO (except for end-of-file).
93 * If a page does not map to a contiguous run of blocks then it simply falls
94 * back to block_read_full_page().
95 *
96 * Why is this?  If a page's completion depends on a number of different BIOs
97 * which can complete in any order (or at the same time) then determining the
98 * status of that page is hard.  See end_buffer_async_read() for the details.
99 * There is no point in duplicating all that complexity.
100 */
101static void mpage_end_io(struct bio *bio, int err)
102{
103	struct bio_vec *bv;
104	int i;
105
106	if (ext4_bio_encrypted(bio)) {
107		struct ext4_crypto_ctx *ctx = bio->bi_private;
108
109		if (err) {
110			ext4_release_crypto_ctx(ctx);
111		} else {
112			INIT_WORK(&ctx->work, completion_pages);
113			ctx->bio = bio;
114			queue_work(ext4_read_workqueue, &ctx->work);
115			return;
116		}
117	}
118	bio_for_each_segment_all(bv, bio, i) {
119		struct page *page = bv->bv_page;
120
121		if (!err) {
122			SetPageUptodate(page);
123		} else {
124			ClearPageUptodate(page);
125			SetPageError(page);
126		}
127		unlock_page(page);
128	}
129
130	bio_put(bio);
131}
132
133int ext4_mpage_readpages(struct address_space *mapping,
134			 struct list_head *pages, struct page *page,
135			 unsigned nr_pages)
136{
137	struct bio *bio = NULL;
138	unsigned page_idx;
139	sector_t last_block_in_bio = 0;
140
141	struct inode *inode = mapping->host;
142	const unsigned blkbits = inode->i_blkbits;
143	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
144	const unsigned blocksize = 1 << blkbits;
145	sector_t block_in_file;
146	sector_t last_block;
147	sector_t last_block_in_file;
148	sector_t blocks[MAX_BUF_PER_PAGE];
149	unsigned page_block;
150	struct block_device *bdev = inode->i_sb->s_bdev;
151	int length;
152	unsigned relative_block = 0;
153	struct ext4_map_blocks map;
154
155	map.m_pblk = 0;
156	map.m_lblk = 0;
157	map.m_len = 0;
158	map.m_flags = 0;
159
160	for (page_idx = 0; nr_pages; page_idx++, nr_pages--) {
161		int fully_mapped = 1;
162		unsigned first_hole = blocks_per_page;
163
164		prefetchw(&page->flags);
165		if (pages) {
166			page = list_entry(pages->prev, struct page, lru);
167			list_del(&page->lru);
168			if (add_to_page_cache_lru(page, mapping,
169						  page->index, GFP_KERNEL))
170				goto next_page;
171		}
172
173		if (page_has_buffers(page))
174			goto confused;
175
176		block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
177		last_block = block_in_file + nr_pages * blocks_per_page;
178		last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
179		if (last_block > last_block_in_file)
180			last_block = last_block_in_file;
181		page_block = 0;
182
183		/*
184		 * Map blocks using the previous result first.
185		 */
186		if ((map.m_flags & EXT4_MAP_MAPPED) &&
187		    block_in_file > map.m_lblk &&
188		    block_in_file < (map.m_lblk + map.m_len)) {
189			unsigned map_offset = block_in_file - map.m_lblk;
190			unsigned last = map.m_len - map_offset;
191
192			for (relative_block = 0; ; relative_block++) {
193				if (relative_block == last) {
194					/* needed? */
195					map.m_flags &= ~EXT4_MAP_MAPPED;
196					break;
197				}
198				if (page_block == blocks_per_page)
199					break;
200				blocks[page_block] = map.m_pblk + map_offset +
201					relative_block;
202				page_block++;
203				block_in_file++;
204			}
205		}
206
207		/*
208		 * Then do more ext4_map_blocks() calls until we are
209		 * done with this page.
210		 */
211		while (page_block < blocks_per_page) {
212			if (block_in_file < last_block) {
213				map.m_lblk = block_in_file;
214				map.m_len = last_block - block_in_file;
215
216				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
217				set_error_page:
218					SetPageError(page);
219					zero_user_segment(page, 0,
220							  PAGE_CACHE_SIZE);
221					unlock_page(page);
222					goto next_page;
223				}
224			}
225			if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
226				fully_mapped = 0;
227				if (first_hole == blocks_per_page)
228					first_hole = page_block;
229				page_block++;
230				block_in_file++;
231				continue;
232			}
233			if (first_hole != blocks_per_page)
234				goto confused;		/* hole -> non-hole */
235
236			/* Contiguous blocks? */
237			if (page_block && blocks[page_block-1] != map.m_pblk-1)
238				goto confused;
239			for (relative_block = 0; ; relative_block++) {
240				if (relative_block == map.m_len) {
241					/* needed? */
242					map.m_flags &= ~EXT4_MAP_MAPPED;
243					break;
244				} else if (page_block == blocks_per_page)
245					break;
246				blocks[page_block] = map.m_pblk+relative_block;
247				page_block++;
248				block_in_file++;
249			}
250		}
251		if (first_hole != blocks_per_page) {
252			zero_user_segment(page, first_hole << blkbits,
253					  PAGE_CACHE_SIZE);
254			if (first_hole == 0) {
255				SetPageUptodate(page);
256				unlock_page(page);
257				goto next_page;
258			}
259		} else if (fully_mapped) {
260			SetPageMappedToDisk(page);
261		}
262		if (fully_mapped && blocks_per_page == 1 &&
263		    !PageUptodate(page) && cleancache_get_page(page) == 0) {
264			SetPageUptodate(page);
265			goto confused;
266		}
267
268		/*
269		 * This page will go to BIO.  Do we need to send this
270		 * BIO off first?
271		 */
272		if (bio && (last_block_in_bio != blocks[0] - 1)) {
273		submit_and_realloc:
274			submit_bio(READ, bio);
275			bio = NULL;
276		}
277		if (bio == NULL) {
278			struct ext4_crypto_ctx *ctx = NULL;
279
280			if (ext4_encrypted_inode(inode) &&
281			    S_ISREG(inode->i_mode)) {
282				ctx = ext4_get_crypto_ctx(inode);
283				if (IS_ERR(ctx))
284					goto set_error_page;
285			}
286			bio = bio_alloc(GFP_KERNEL,
287				min_t(int, nr_pages, bio_get_nr_vecs(bdev)));
288			if (!bio) {
289				if (ctx)
290					ext4_release_crypto_ctx(ctx);
291				goto set_error_page;
292			}
293			bio->bi_bdev = bdev;
294			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
295			bio->bi_end_io = mpage_end_io;
296			bio->bi_private = ctx;
297		}
298
299		length = first_hole << blkbits;
300		if (bio_add_page(bio, page, length, 0) < length)
301			goto submit_and_realloc;
302
303		if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
304		     (relative_block == map.m_len)) ||
305		    (first_hole != blocks_per_page)) {
306			submit_bio(READ, bio);
307			bio = NULL;
308		} else
309			last_block_in_bio = blocks[blocks_per_page - 1];
310		goto next_page;
311	confused:
312		if (bio) {
313			submit_bio(READ, bio);
314			bio = NULL;
315		}
316		if (!PageUptodate(page))
317			block_read_full_page(page, ext4_get_block);
318		else
319			unlock_page(page);
320	next_page:
321		if (pages)
322			page_cache_release(page);
323	}
324	BUG_ON(pages && !list_empty(pages));
325	if (bio)
326		submit_bio(READ, bio);
327	return 0;
328}
329