buffered-io.c revision b74b1293
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2010 Red Hat, Inc.
4 * Copyright (C) 2016-2019 Christoph Hellwig.
5 */
6#include <linux/module.h>
7#include <linux/compiler.h>
8#include <linux/fs.h>
9#include <linux/iomap.h>
10#include <linux/pagemap.h>
11#include <linux/uio.h>
12#include <linux/buffer_head.h>
13#include <linux/dax.h>
14#include <linux/writeback.h>
15#include <linux/list_sort.h>
16#include <linux/swap.h>
17#include <linux/bio.h>
18#include <linux/sched/signal.h>
19#include <linux/migrate.h>
20#include "trace.h"
21
22#include "../internal.h"
23
24/*
25 * Structure allocated for each page or THP when block size < page size
26 * to track sub-page uptodate status and I/O completions.
27 */
28struct iomap_page {
29	atomic_t		read_bytes_pending;
30	atomic_t		write_bytes_pending;
31	spinlock_t		uptodate_lock;
32	unsigned long		uptodate[];
33};
34
35static inline struct iomap_page *to_iomap_page(struct page *page)
36{
37	/*
38	 * per-block data is stored in the head page.  Callers should
39	 * not be dealing with tail pages, and if they are, they can
40	 * call thp_head() first.
41	 */
42	VM_BUG_ON_PGFLAGS(PageTail(page), page);
43
44	if (page_has_private(page))
45		return (struct iomap_page *)page_private(page);
46	return NULL;
47}
48
49static struct bio_set iomap_ioend_bioset;
50
51static struct iomap_page *
52iomap_page_create(struct inode *inode, struct page *page)
53{
54	struct iomap_page *iop = to_iomap_page(page);
55	unsigned int nr_blocks = i_blocks_per_page(inode, page);
56
57	if (iop || nr_blocks <= 1)
58		return iop;
59
60	iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),
61			GFP_NOFS | __GFP_NOFAIL);
62	spin_lock_init(&iop->uptodate_lock);
63	if (PageUptodate(page))
64		bitmap_fill(iop->uptodate, nr_blocks);
65	attach_page_private(page, iop);
66	return iop;
67}
68
69static void
70iomap_page_release(struct page *page)
71{
72	struct iomap_page *iop = detach_page_private(page);
73	unsigned int nr_blocks = i_blocks_per_page(page->mapping->host, page);
74
75	if (!iop)
76		return;
77	WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
78	WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
79	WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
80			PageUptodate(page));
81	kfree(iop);
82}
83
84/*
85 * Calculate the range inside the page that we actually need to read.
86 */
87static void
88iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
89		loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)
90{
91	loff_t orig_pos = *pos;
92	loff_t isize = i_size_read(inode);
93	unsigned block_bits = inode->i_blkbits;
94	unsigned block_size = (1 << block_bits);
95	unsigned poff = offset_in_page(*pos);
96	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
97	unsigned first = poff >> block_bits;
98	unsigned last = (poff + plen - 1) >> block_bits;
99
100	/*
101	 * If the block size is smaller than the page size, we need to check the
102	 * per-block uptodate status and adjust the offset and length if needed
103	 * to avoid reading in already uptodate ranges.
104	 */
105	if (iop) {
106		unsigned int i;
107
108		/* move forward for each leading block marked uptodate */
109		for (i = first; i <= last; i++) {
110			if (!test_bit(i, iop->uptodate))
111				break;
112			*pos += block_size;
113			poff += block_size;
114			plen -= block_size;
115			first++;
116		}
117
118		/* truncate len if we find any trailing uptodate block(s) */
119		for ( ; i <= last; i++) {
120			if (test_bit(i, iop->uptodate)) {
121				plen -= (last - i + 1) * block_size;
122				last = i - 1;
123				break;
124			}
125		}
126	}
127
128	/*
129	 * If the extent spans the block that contains the i_size, we need to
130	 * handle both halves separately so that we properly zero data in the
131	 * page cache for blocks that are entirely outside of i_size.
132	 */
133	if (orig_pos <= isize && orig_pos + length > isize) {
134		unsigned end = offset_in_page(isize - 1) >> block_bits;
135
136		if (first <= end && last > end)
137			plen -= (last - end) * block_size;
138	}
139
140	*offp = poff;
141	*lenp = plen;
142}
143
144static void
145iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
146{
147	struct iomap_page *iop = to_iomap_page(page);
148	struct inode *inode = page->mapping->host;
149	unsigned first = off >> inode->i_blkbits;
150	unsigned last = (off + len - 1) >> inode->i_blkbits;
151	unsigned long flags;
152
153	spin_lock_irqsave(&iop->uptodate_lock, flags);
154	bitmap_set(iop->uptodate, first, last - first + 1);
155	if (bitmap_full(iop->uptodate, i_blocks_per_page(inode, page)))
156		SetPageUptodate(page);
157	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
158}
159
160static void
161iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
162{
163	if (PageError(page))
164		return;
165
166	if (page_has_private(page))
167		iomap_iop_set_range_uptodate(page, off, len);
168	else
169		SetPageUptodate(page);
170}
171
172static void
173iomap_read_page_end_io(struct bio_vec *bvec, int error)
174{
175	struct page *page = bvec->bv_page;
176	struct iomap_page *iop = to_iomap_page(page);
177
178	if (unlikely(error)) {
179		ClearPageUptodate(page);
180		SetPageError(page);
181	} else {
182		iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
183	}
184
185	if (!iop || atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending))
186		unlock_page(page);
187}
188
189static void
190iomap_read_end_io(struct bio *bio)
191{
192	int error = blk_status_to_errno(bio->bi_status);
193	struct bio_vec *bvec;
194	struct bvec_iter_all iter_all;
195
196	bio_for_each_segment_all(bvec, bio, iter_all)
197		iomap_read_page_end_io(bvec, error);
198	bio_put(bio);
199}
200
201struct iomap_readpage_ctx {
202	struct page		*cur_page;
203	bool			cur_page_in_bio;
204	struct bio		*bio;
205	struct readahead_control *rac;
206};
207
208static loff_t iomap_read_inline_data(struct iomap_iter *iter,
209		struct page *page)
210{
211	struct iomap *iomap = iomap_iter_srcmap(iter);
212	size_t size = i_size_read(iter->inode) - iomap->offset;
213	size_t poff = offset_in_page(iomap->offset);
214	void *addr;
215
216	if (PageUptodate(page))
217		return PAGE_SIZE - poff;
218
219	if (WARN_ON_ONCE(size > PAGE_SIZE - poff))
220		return -EIO;
221	if (WARN_ON_ONCE(size > PAGE_SIZE -
222			 offset_in_page(iomap->inline_data)))
223		return -EIO;
224	if (WARN_ON_ONCE(size > iomap->length))
225		return -EIO;
226	if (poff > 0)
227		iomap_page_create(iter->inode, page);
228
229	addr = kmap_local_page(page) + poff;
230	memcpy(addr, iomap->inline_data, size);
231	memset(addr + size, 0, PAGE_SIZE - poff - size);
232	kunmap_local(addr);
233	iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
234	return PAGE_SIZE - poff;
235}
236
237static inline bool iomap_block_needs_zeroing(struct iomap_iter *iter,
238		loff_t pos)
239{
240	struct iomap *srcmap = iomap_iter_srcmap(iter);
241
242	return srcmap->type != IOMAP_MAPPED ||
243		(srcmap->flags & IOMAP_F_NEW) ||
244		pos >= i_size_read(iter->inode);
245}
246
247static loff_t iomap_readpage_iter(struct iomap_iter *iter,
248		struct iomap_readpage_ctx *ctx, loff_t offset)
249{
250	struct iomap *iomap = &iter->iomap;
251	loff_t pos = iter->pos + offset;
252	loff_t length = iomap_length(iter) - offset;
253	struct page *page = ctx->cur_page;
254	struct iomap_page *iop;
255	loff_t orig_pos = pos;
256	unsigned poff, plen;
257	sector_t sector;
258
259	if (iomap->type == IOMAP_INLINE)
260		return min(iomap_read_inline_data(iter, page), length);
261
262	/* zero post-eof blocks as the page may be mapped */
263	iop = iomap_page_create(iter->inode, page);
264	iomap_adjust_read_range(iter->inode, iop, &pos, length, &poff, &plen);
265	if (plen == 0)
266		goto done;
267
268	if (iomap_block_needs_zeroing(iter, pos)) {
269		zero_user(page, poff, plen);
270		iomap_set_range_uptodate(page, poff, plen);
271		goto done;
272	}
273
274	ctx->cur_page_in_bio = true;
275	if (iop)
276		atomic_add(plen, &iop->read_bytes_pending);
277
278	sector = iomap_sector(iomap, pos);
279	if (!ctx->bio ||
280	    bio_end_sector(ctx->bio) != sector ||
281	    bio_add_page(ctx->bio, page, plen, poff) != plen) {
282		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
283		gfp_t orig_gfp = gfp;
284		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
285
286		if (ctx->bio)
287			submit_bio(ctx->bio);
288
289		if (ctx->rac) /* same as readahead_gfp_mask */
290			gfp |= __GFP_NORETRY | __GFP_NOWARN;
291		ctx->bio = bio_alloc(gfp, bio_max_segs(nr_vecs));
292		/*
293		 * If the bio_alloc fails, try it again for a single page to
294		 * avoid having to deal with partial page reads.  This emulates
295		 * what do_mpage_readpage does.
296		 */
297		if (!ctx->bio)
298			ctx->bio = bio_alloc(orig_gfp, 1);
299		ctx->bio->bi_opf = REQ_OP_READ;
300		if (ctx->rac)
301			ctx->bio->bi_opf |= REQ_RAHEAD;
302		ctx->bio->bi_iter.bi_sector = sector;
303		bio_set_dev(ctx->bio, iomap->bdev);
304		ctx->bio->bi_end_io = iomap_read_end_io;
305		__bio_add_page(ctx->bio, page, plen, poff);
306	}
307done:
308	/*
309	 * Move the caller beyond our range so that it keeps making progress.
310	 * For that, we have to include any leading non-uptodate ranges, but
311	 * we can skip trailing ones as they will be handled in the next
312	 * iteration.
313	 */
314	return pos - orig_pos + plen;
315}
316
317int
318iomap_readpage(struct page *page, const struct iomap_ops *ops)
319{
320	struct iomap_iter iter = {
321		.inode		= page->mapping->host,
322		.pos		= page_offset(page),
323		.len		= PAGE_SIZE,
324	};
325	struct iomap_readpage_ctx ctx = {
326		.cur_page	= page,
327	};
328	int ret;
329
330	trace_iomap_readpage(page->mapping->host, 1);
331
332	while ((ret = iomap_iter(&iter, ops)) > 0)
333		iter.processed = iomap_readpage_iter(&iter, &ctx, 0);
334
335	if (ret < 0)
336		SetPageError(page);
337
338	if (ctx.bio) {
339		submit_bio(ctx.bio);
340		WARN_ON_ONCE(!ctx.cur_page_in_bio);
341	} else {
342		WARN_ON_ONCE(ctx.cur_page_in_bio);
343		unlock_page(page);
344	}
345
346	/*
347	 * Just like mpage_readahead and block_read_full_page, we always
348	 * return 0 and just mark the page as PageError on errors.  This
349	 * should be cleaned up throughout the stack eventually.
350	 */
351	return 0;
352}
353EXPORT_SYMBOL_GPL(iomap_readpage);
354
355static loff_t iomap_readahead_iter(struct iomap_iter *iter,
356		struct iomap_readpage_ctx *ctx)
357{
358	loff_t length = iomap_length(iter);
359	loff_t done, ret;
360
361	for (done = 0; done < length; done += ret) {
362		if (ctx->cur_page && offset_in_page(iter->pos + done) == 0) {
363			if (!ctx->cur_page_in_bio)
364				unlock_page(ctx->cur_page);
365			put_page(ctx->cur_page);
366			ctx->cur_page = NULL;
367		}
368		if (!ctx->cur_page) {
369			ctx->cur_page = readahead_page(ctx->rac);
370			ctx->cur_page_in_bio = false;
371		}
372		ret = iomap_readpage_iter(iter, ctx, done);
373	}
374
375	return done;
376}
377
378/**
379 * iomap_readahead - Attempt to read pages from a file.
380 * @rac: Describes the pages to be read.
381 * @ops: The operations vector for the filesystem.
382 *
383 * This function is for filesystems to call to implement their readahead
384 * address_space operation.
385 *
386 * Context: The @ops callbacks may submit I/O (eg to read the addresses of
387 * blocks from disc), and may wait for it.  The caller may be trying to
388 * access a different page, and so sleeping excessively should be avoided.
389 * It may allocate memory, but should avoid costly allocations.  This
390 * function is called with memalloc_nofs set, so allocations will not cause
391 * the filesystem to be reentered.
392 */
393void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
394{
395	struct iomap_iter iter = {
396		.inode	= rac->mapping->host,
397		.pos	= readahead_pos(rac),
398		.len	= readahead_length(rac),
399	};
400	struct iomap_readpage_ctx ctx = {
401		.rac	= rac,
402	};
403
404	trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
405
406	while (iomap_iter(&iter, ops) > 0)
407		iter.processed = iomap_readahead_iter(&iter, &ctx);
408
409	if (ctx.bio)
410		submit_bio(ctx.bio);
411	if (ctx.cur_page) {
412		if (!ctx.cur_page_in_bio)
413			unlock_page(ctx.cur_page);
414		put_page(ctx.cur_page);
415	}
416}
417EXPORT_SYMBOL_GPL(iomap_readahead);
418
419/*
420 * iomap_is_partially_uptodate checks whether blocks within a page are
421 * uptodate or not.
422 *
423 * Returns true if all blocks which correspond to a file portion
424 * we want to read within the page are uptodate.
425 */
426int
427iomap_is_partially_uptodate(struct page *page, unsigned long from,
428		unsigned long count)
429{
430	struct iomap_page *iop = to_iomap_page(page);
431	struct inode *inode = page->mapping->host;
432	unsigned len, first, last;
433	unsigned i;
434
435	/* Limit range to one page */
436	len = min_t(unsigned, PAGE_SIZE - from, count);
437
438	/* First and last blocks in range within page */
439	first = from >> inode->i_blkbits;
440	last = (from + len - 1) >> inode->i_blkbits;
441
442	if (iop) {
443		for (i = first; i <= last; i++)
444			if (!test_bit(i, iop->uptodate))
445				return 0;
446		return 1;
447	}
448
449	return 0;
450}
451EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
452
453int
454iomap_releasepage(struct page *page, gfp_t gfp_mask)
455{
456	trace_iomap_releasepage(page->mapping->host, page_offset(page),
457			PAGE_SIZE);
458
459	/*
460	 * mm accommodates an old ext3 case where clean pages might not have had
461	 * the dirty bit cleared. Thus, it can send actual dirty pages to
462	 * ->releasepage() via shrink_active_list(); skip those here.
463	 */
464	if (PageDirty(page) || PageWriteback(page))
465		return 0;
466	iomap_page_release(page);
467	return 1;
468}
469EXPORT_SYMBOL_GPL(iomap_releasepage);
470
471void
472iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)
473{
474	trace_iomap_invalidatepage(page->mapping->host, offset, len);
475
476	/*
477	 * If we're invalidating the entire page, clear the dirty state from it
478	 * and release it to avoid unnecessary buildup of the LRU.
479	 */
480	if (offset == 0 && len == PAGE_SIZE) {
481		WARN_ON_ONCE(PageWriteback(page));
482		cancel_dirty_page(page);
483		iomap_page_release(page);
484	}
485}
486EXPORT_SYMBOL_GPL(iomap_invalidatepage);
487
488#ifdef CONFIG_MIGRATION
489int
490iomap_migrate_page(struct address_space *mapping, struct page *newpage,
491		struct page *page, enum migrate_mode mode)
492{
493	int ret;
494
495	ret = migrate_page_move_mapping(mapping, newpage, page, 0);
496	if (ret != MIGRATEPAGE_SUCCESS)
497		return ret;
498
499	if (page_has_private(page))
500		attach_page_private(newpage, detach_page_private(page));
501
502	if (mode != MIGRATE_SYNC_NO_COPY)
503		migrate_page_copy(newpage, page);
504	else
505		migrate_page_states(newpage, page);
506	return MIGRATEPAGE_SUCCESS;
507}
508EXPORT_SYMBOL_GPL(iomap_migrate_page);
509#endif /* CONFIG_MIGRATION */
510
511static void
512iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
513{
514	loff_t i_size = i_size_read(inode);
515
516	/*
517	 * Only truncate newly allocated pages beyoned EOF, even if the
518	 * write started inside the existing inode size.
519	 */
520	if (pos + len > i_size)
521		truncate_pagecache_range(inode, max(pos, i_size), pos + len);
522}
523
524static int
525iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff,
526		unsigned plen, const struct iomap *iomap)
527{
528	struct bio_vec bvec;
529	struct bio bio;
530
531	bio_init(&bio, &bvec, 1);
532	bio.bi_opf = REQ_OP_READ;
533	bio.bi_iter.bi_sector = iomap_sector(iomap, block_start);
534	bio_set_dev(&bio, iomap->bdev);
535	__bio_add_page(&bio, page, plen, poff);
536	return submit_bio_wait(&bio);
537}
538
539static int __iomap_write_begin(struct iomap_iter *iter, loff_t pos,
540		unsigned len, struct page *page)
541{
542	struct iomap *srcmap = iomap_iter_srcmap(iter);
543	struct iomap_page *iop = iomap_page_create(iter->inode, page);
544	loff_t block_size = i_blocksize(iter->inode);
545	loff_t block_start = round_down(pos, block_size);
546	loff_t block_end = round_up(pos + len, block_size);
547	unsigned from = offset_in_page(pos), to = from + len, poff, plen;
548
549	if (PageUptodate(page))
550		return 0;
551	ClearPageError(page);
552
553	do {
554		iomap_adjust_read_range(iter->inode, iop, &block_start,
555				block_end - block_start, &poff, &plen);
556		if (plen == 0)
557			break;
558
559		if (!(iter->flags & IOMAP_UNSHARE) &&
560		    (from <= poff || from >= poff + plen) &&
561		    (to <= poff || to >= poff + plen))
562			continue;
563
564		if (iomap_block_needs_zeroing(iter, block_start)) {
565			if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE))
566				return -EIO;
567			zero_user_segments(page, poff, from, to, poff + plen);
568		} else {
569			int status = iomap_read_page_sync(block_start, page,
570					poff, plen, srcmap);
571			if (status)
572				return status;
573		}
574		iomap_set_range_uptodate(page, poff, plen);
575	} while ((block_start += plen) < block_end);
576
577	return 0;
578}
579
580static int iomap_write_begin_inline(struct iomap_iter *iter,
581		struct page *page)
582{
583	int ret;
584
585	/* needs more work for the tailpacking case; disable for now */
586	if (WARN_ON_ONCE(iomap_iter_srcmap(iter)->offset != 0))
587		return -EIO;
588	ret = iomap_read_inline_data(iter, page);
589	if (ret < 0)
590		return ret;
591	return 0;
592}
593
594static int iomap_write_begin(struct iomap_iter *iter, loff_t pos, unsigned len,
595		struct page **pagep)
596{
597	const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
598	struct iomap *srcmap = iomap_iter_srcmap(iter);
599	struct page *page;
600	int status = 0;
601
602	BUG_ON(pos + len > iter->iomap.offset + iter->iomap.length);
603	if (srcmap != &iter->iomap)
604		BUG_ON(pos + len > srcmap->offset + srcmap->length);
605
606	if (fatal_signal_pending(current))
607		return -EINTR;
608
609	if (page_ops && page_ops->page_prepare) {
610		status = page_ops->page_prepare(iter->inode, pos, len);
611		if (status)
612			return status;
613	}
614
615	page = grab_cache_page_write_begin(iter->inode->i_mapping,
616				pos >> PAGE_SHIFT, AOP_FLAG_NOFS);
617	if (!page) {
618		status = -ENOMEM;
619		goto out_no_page;
620	}
621
622	if (srcmap->type == IOMAP_INLINE)
623		status = iomap_write_begin_inline(iter, page);
624	else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
625		status = __block_write_begin_int(page, pos, len, NULL, srcmap);
626	else
627		status = __iomap_write_begin(iter, pos, len, page);
628
629	if (unlikely(status))
630		goto out_unlock;
631
632	*pagep = page;
633	return 0;
634
635out_unlock:
636	unlock_page(page);
637	put_page(page);
638	iomap_write_failed(iter->inode, pos, len);
639
640out_no_page:
641	if (page_ops && page_ops->page_done)
642		page_ops->page_done(iter->inode, pos, 0, NULL);
643	return status;
644}
645
646static size_t __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
647		size_t copied, struct page *page)
648{
649	flush_dcache_page(page);
650
651	/*
652	 * The blocks that were entirely written will now be uptodate, so we
653	 * don't have to worry about a readpage reading them and overwriting a
654	 * partial write.  However, if we've encountered a short write and only
655	 * partially written into a block, it will not be marked uptodate, so a
656	 * readpage might come in and destroy our partial write.
657	 *
658	 * Do the simplest thing and just treat any short write to a
659	 * non-uptodate page as a zero-length write, and force the caller to
660	 * redo the whole thing.
661	 */
662	if (unlikely(copied < len && !PageUptodate(page)))
663		return 0;
664	iomap_set_range_uptodate(page, offset_in_page(pos), len);
665	__set_page_dirty_nobuffers(page);
666	return copied;
667}
668
669static size_t iomap_write_end_inline(struct iomap_iter *iter, struct page *page,
670		loff_t pos, size_t copied)
671{
672	struct iomap *iomap = &iter->iomap;
673	void *addr;
674
675	WARN_ON_ONCE(!PageUptodate(page));
676	BUG_ON(!iomap_inline_data_valid(iomap));
677
678	flush_dcache_page(page);
679	addr = kmap_local_page(page) + pos;
680	memcpy(iomap_inline_data(iomap, pos), addr, copied);
681	kunmap_local(addr);
682
683	mark_inode_dirty(iter->inode);
684	return copied;
685}
686
687/* Returns the number of bytes copied.  May be 0.  Cannot be an errno. */
688static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
689		size_t copied, struct page *page)
690{
691	const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
692	struct iomap *srcmap = iomap_iter_srcmap(iter);
693	loff_t old_size = iter->inode->i_size;
694	size_t ret;
695
696	if (srcmap->type == IOMAP_INLINE) {
697		ret = iomap_write_end_inline(iter, page, pos, copied);
698	} else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
699		ret = block_write_end(NULL, iter->inode->i_mapping, pos, len,
700				copied, page, NULL);
701	} else {
702		ret = __iomap_write_end(iter->inode, pos, len, copied, page);
703	}
704
705	/*
706	 * Update the in-memory inode size after copying the data into the page
707	 * cache.  It's up to the file system to write the updated size to disk,
708	 * preferably after I/O completion so that no stale data is exposed.
709	 */
710	if (pos + ret > old_size) {
711		i_size_write(iter->inode, pos + ret);
712		iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
713	}
714	unlock_page(page);
715
716	if (old_size < pos)
717		pagecache_isize_extended(iter->inode, old_size, pos);
718	if (page_ops && page_ops->page_done)
719		page_ops->page_done(iter->inode, pos, ret, page);
720	put_page(page);
721
722	if (ret < len)
723		iomap_write_failed(iter->inode, pos, len);
724	return ret;
725}
726
727static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
728{
729	loff_t length = iomap_length(iter);
730	loff_t pos = iter->pos;
731	ssize_t written = 0;
732	long status = 0;
733
734	do {
735		struct page *page;
736		unsigned long offset;	/* Offset into pagecache page */
737		unsigned long bytes;	/* Bytes to write to page */
738		size_t copied;		/* Bytes copied from user */
739
740		offset = offset_in_page(pos);
741		bytes = min_t(unsigned long, PAGE_SIZE - offset,
742						iov_iter_count(i));
743again:
744		if (bytes > length)
745			bytes = length;
746
747		/*
748		 * Bring in the user page that we'll copy from _first_.
749		 * Otherwise there's a nasty deadlock on copying from the
750		 * same page as we're writing to, without it being marked
751		 * up-to-date.
752		 */
753		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
754			status = -EFAULT;
755			break;
756		}
757
758		status = iomap_write_begin(iter, pos, bytes, &page);
759		if (unlikely(status))
760			break;
761
762		if (mapping_writably_mapped(iter->inode->i_mapping))
763			flush_dcache_page(page);
764
765		copied = copy_page_from_iter_atomic(page, offset, bytes, i);
766
767		status = iomap_write_end(iter, pos, bytes, copied, page);
768
769		if (unlikely(copied != status))
770			iov_iter_revert(i, copied - status);
771
772		cond_resched();
773		if (unlikely(status == 0)) {
774			/*
775			 * A short copy made iomap_write_end() reject the
776			 * thing entirely.  Might be memory poisoning
777			 * halfway through, might be a race with munmap,
778			 * might be severe memory pressure.
779			 */
780			if (copied)
781				bytes = copied;
782			goto again;
783		}
784		pos += status;
785		written += status;
786		length -= status;
787
788		balance_dirty_pages_ratelimited(iter->inode->i_mapping);
789	} while (iov_iter_count(i) && length);
790
791	return written ? written : status;
792}
793
794ssize_t
795iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
796		const struct iomap_ops *ops)
797{
798	struct iomap_iter iter = {
799		.inode		= iocb->ki_filp->f_mapping->host,
800		.pos		= iocb->ki_pos,
801		.len		= iov_iter_count(i),
802		.flags		= IOMAP_WRITE,
803	};
804	int ret;
805
806	while ((ret = iomap_iter(&iter, ops)) > 0)
807		iter.processed = iomap_write_iter(&iter, i);
808	if (iter.pos == iocb->ki_pos)
809		return ret;
810	return iter.pos - iocb->ki_pos;
811}
812EXPORT_SYMBOL_GPL(iomap_file_buffered_write);
813
814static loff_t iomap_unshare_iter(struct iomap_iter *iter)
815{
816	struct iomap *iomap = &iter->iomap;
817	struct iomap *srcmap = iomap_iter_srcmap(iter);
818	loff_t pos = iter->pos;
819	loff_t length = iomap_length(iter);
820	long status = 0;
821	loff_t written = 0;
822
823	/* don't bother with blocks that are not shared to start with */
824	if (!(iomap->flags & IOMAP_F_SHARED))
825		return length;
826	/* don't bother with holes or unwritten extents */
827	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
828		return length;
829
830	do {
831		unsigned long offset = offset_in_page(pos);
832		unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length);
833		struct page *page;
834
835		status = iomap_write_begin(iter, pos, bytes, &page);
836		if (unlikely(status))
837			return status;
838
839		status = iomap_write_end(iter, pos, bytes, bytes, page);
840		if (WARN_ON_ONCE(status == 0))
841			return -EIO;
842
843		cond_resched();
844
845		pos += status;
846		written += status;
847		length -= status;
848
849		balance_dirty_pages_ratelimited(iter->inode->i_mapping);
850	} while (length);
851
852	return written;
853}
854
855int
856iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
857		const struct iomap_ops *ops)
858{
859	struct iomap_iter iter = {
860		.inode		= inode,
861		.pos		= pos,
862		.len		= len,
863		.flags		= IOMAP_WRITE | IOMAP_UNSHARE,
864	};
865	int ret;
866
867	while ((ret = iomap_iter(&iter, ops)) > 0)
868		iter.processed = iomap_unshare_iter(&iter);
869	return ret;
870}
871EXPORT_SYMBOL_GPL(iomap_file_unshare);
872
873static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
874{
875	struct page *page;
876	int status;
877	unsigned offset = offset_in_page(pos);
878	unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
879
880	status = iomap_write_begin(iter, pos, bytes, &page);
881	if (status)
882		return status;
883
884	zero_user(page, offset, bytes);
885	mark_page_accessed(page);
886
887	return iomap_write_end(iter, pos, bytes, bytes, page);
888}
889
890static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
891{
892	struct iomap *iomap = &iter->iomap;
893	struct iomap *srcmap = iomap_iter_srcmap(iter);
894	loff_t pos = iter->pos;
895	loff_t length = iomap_length(iter);
896	loff_t written = 0;
897
898	/* already zeroed?  we're done. */
899	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
900		return length;
901
902	do {
903		s64 bytes;
904
905		if (IS_DAX(iter->inode))
906			bytes = dax_iomap_zero(pos, length, iomap);
907		else
908			bytes = __iomap_zero_iter(iter, pos, length);
909		if (bytes < 0)
910			return bytes;
911
912		pos += bytes;
913		length -= bytes;
914		written += bytes;
915		if (did_zero)
916			*did_zero = true;
917	} while (length > 0);
918
919	return written;
920}
921
922int
923iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
924		const struct iomap_ops *ops)
925{
926	struct iomap_iter iter = {
927		.inode		= inode,
928		.pos		= pos,
929		.len		= len,
930		.flags		= IOMAP_ZERO,
931	};
932	int ret;
933
934	while ((ret = iomap_iter(&iter, ops)) > 0)
935		iter.processed = iomap_zero_iter(&iter, did_zero);
936	return ret;
937}
938EXPORT_SYMBOL_GPL(iomap_zero_range);
939
940int
941iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
942		const struct iomap_ops *ops)
943{
944	unsigned int blocksize = i_blocksize(inode);
945	unsigned int off = pos & (blocksize - 1);
946
947	/* Block boundary? Nothing to do */
948	if (!off)
949		return 0;
950	return iomap_zero_range(inode, pos, blocksize - off, did_zero, ops);
951}
952EXPORT_SYMBOL_GPL(iomap_truncate_page);
953
954static loff_t iomap_page_mkwrite_iter(struct iomap_iter *iter,
955		struct page *page)
956{
957	loff_t length = iomap_length(iter);
958	int ret;
959
960	if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
961		ret = __block_write_begin_int(page, iter->pos, length, NULL,
962					      &iter->iomap);
963		if (ret)
964			return ret;
965		block_commit_write(page, 0, length);
966	} else {
967		WARN_ON_ONCE(!PageUptodate(page));
968		set_page_dirty(page);
969	}
970
971	return length;
972}
973
974vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
975{
976	struct iomap_iter iter = {
977		.inode		= file_inode(vmf->vma->vm_file),
978		.flags		= IOMAP_WRITE | IOMAP_FAULT,
979	};
980	struct page *page = vmf->page;
981	ssize_t ret;
982
983	lock_page(page);
984	ret = page_mkwrite_check_truncate(page, iter.inode);
985	if (ret < 0)
986		goto out_unlock;
987	iter.pos = page_offset(page);
988	iter.len = ret;
989	while ((ret = iomap_iter(&iter, ops)) > 0)
990		iter.processed = iomap_page_mkwrite_iter(&iter, page);
991
992	if (ret < 0)
993		goto out_unlock;
994	wait_for_stable_page(page);
995	return VM_FAULT_LOCKED;
996out_unlock:
997	unlock_page(page);
998	return block_page_mkwrite_return(ret);
999}
1000EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
1001
1002static void
1003iomap_finish_page_writeback(struct inode *inode, struct page *page,
1004		int error, unsigned int len)
1005{
1006	struct iomap_page *iop = to_iomap_page(page);
1007
1008	if (error) {
1009		SetPageError(page);
1010		mapping_set_error(inode->i_mapping, error);
1011	}
1012
1013	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
1014	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) <= 0);
1015
1016	if (!iop || atomic_sub_and_test(len, &iop->write_bytes_pending))
1017		end_page_writeback(page);
1018}
1019
1020/*
1021 * We're now finished for good with this ioend structure.  Update the page
1022 * state, release holds on bios, and finally free up memory.  Do not use the
1023 * ioend after this.
1024 */
1025static void
1026iomap_finish_ioend(struct iomap_ioend *ioend, int error)
1027{
1028	struct inode *inode = ioend->io_inode;
1029	struct bio *bio = &ioend->io_inline_bio;
1030	struct bio *last = ioend->io_bio, *next;
1031	u64 start = bio->bi_iter.bi_sector;
1032	loff_t offset = ioend->io_offset;
1033	bool quiet = bio_flagged(bio, BIO_QUIET);
1034
1035	for (bio = &ioend->io_inline_bio; bio; bio = next) {
1036		struct bio_vec *bv;
1037		struct bvec_iter_all iter_all;
1038
1039		/*
1040		 * For the last bio, bi_private points to the ioend, so we
1041		 * need to explicitly end the iteration here.
1042		 */
1043		if (bio == last)
1044			next = NULL;
1045		else
1046			next = bio->bi_private;
1047
1048		/* walk each page on bio, ending page IO on them */
1049		bio_for_each_segment_all(bv, bio, iter_all)
1050			iomap_finish_page_writeback(inode, bv->bv_page, error,
1051					bv->bv_len);
1052		bio_put(bio);
1053	}
1054	/* The ioend has been freed by bio_put() */
1055
1056	if (unlikely(error && !quiet)) {
1057		printk_ratelimited(KERN_ERR
1058"%s: writeback error on inode %lu, offset %lld, sector %llu",
1059			inode->i_sb->s_id, inode->i_ino, offset, start);
1060	}
1061}
1062
1063void
1064iomap_finish_ioends(struct iomap_ioend *ioend, int error)
1065{
1066	struct list_head tmp;
1067
1068	list_replace_init(&ioend->io_list, &tmp);
1069	iomap_finish_ioend(ioend, error);
1070
1071	while (!list_empty(&tmp)) {
1072		ioend = list_first_entry(&tmp, struct iomap_ioend, io_list);
1073		list_del_init(&ioend->io_list);
1074		iomap_finish_ioend(ioend, error);
1075	}
1076}
1077EXPORT_SYMBOL_GPL(iomap_finish_ioends);
1078
1079/*
1080 * We can merge two adjacent ioends if they have the same set of work to do.
1081 */
1082static bool
1083iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
1084{
1085	if (ioend->io_bio->bi_status != next->io_bio->bi_status)
1086		return false;
1087	if ((ioend->io_flags & IOMAP_F_SHARED) ^
1088	    (next->io_flags & IOMAP_F_SHARED))
1089		return false;
1090	if ((ioend->io_type == IOMAP_UNWRITTEN) ^
1091	    (next->io_type == IOMAP_UNWRITTEN))
1092		return false;
1093	if (ioend->io_offset + ioend->io_size != next->io_offset)
1094		return false;
1095	return true;
1096}
1097
1098void
1099iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends)
1100{
1101	struct iomap_ioend *next;
1102
1103	INIT_LIST_HEAD(&ioend->io_list);
1104
1105	while ((next = list_first_entry_or_null(more_ioends, struct iomap_ioend,
1106			io_list))) {
1107		if (!iomap_ioend_can_merge(ioend, next))
1108			break;
1109		list_move_tail(&next->io_list, &ioend->io_list);
1110		ioend->io_size += next->io_size;
1111	}
1112}
1113EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
1114
1115static int
1116iomap_ioend_compare(void *priv, const struct list_head *a,
1117		const struct list_head *b)
1118{
1119	struct iomap_ioend *ia = container_of(a, struct iomap_ioend, io_list);
1120	struct iomap_ioend *ib = container_of(b, struct iomap_ioend, io_list);
1121
1122	if (ia->io_offset < ib->io_offset)
1123		return -1;
1124	if (ia->io_offset > ib->io_offset)
1125		return 1;
1126	return 0;
1127}
1128
1129void
1130iomap_sort_ioends(struct list_head *ioend_list)
1131{
1132	list_sort(NULL, ioend_list, iomap_ioend_compare);
1133}
1134EXPORT_SYMBOL_GPL(iomap_sort_ioends);
1135
1136static void iomap_writepage_end_bio(struct bio *bio)
1137{
1138	struct iomap_ioend *ioend = bio->bi_private;
1139
1140	iomap_finish_ioend(ioend, blk_status_to_errno(bio->bi_status));
1141}
1142
1143/*
1144 * Submit the final bio for an ioend.
1145 *
1146 * If @error is non-zero, it means that we have a situation where some part of
1147 * the submission process has failed after we've marked pages for writeback
1148 * and unlocked them.  In this situation, we need to fail the bio instead of
1149 * submitting it.  This typically only happens on a filesystem shutdown.
1150 */
1151static int
1152iomap_submit_ioend(struct iomap_writepage_ctx *wpc, struct iomap_ioend *ioend,
1153		int error)
1154{
1155	ioend->io_bio->bi_private = ioend;
1156	ioend->io_bio->bi_end_io = iomap_writepage_end_bio;
1157
1158	if (wpc->ops->prepare_ioend)
1159		error = wpc->ops->prepare_ioend(ioend, error);
1160	if (error) {
1161		/*
1162		 * If we're failing the IO now, just mark the ioend with an
1163		 * error and finish it.  This will run IO completion immediately
1164		 * as there is only one reference to the ioend at this point in
1165		 * time.
1166		 */
1167		ioend->io_bio->bi_status = errno_to_blk_status(error);
1168		bio_endio(ioend->io_bio);
1169		return error;
1170	}
1171
1172	submit_bio(ioend->io_bio);
1173	return 0;
1174}
1175
1176static struct iomap_ioend *
1177iomap_alloc_ioend(struct inode *inode, struct iomap_writepage_ctx *wpc,
1178		loff_t offset, sector_t sector, struct writeback_control *wbc)
1179{
1180	struct iomap_ioend *ioend;
1181	struct bio *bio;
1182
1183	bio = bio_alloc_bioset(GFP_NOFS, BIO_MAX_VECS, &iomap_ioend_bioset);
1184	bio_set_dev(bio, wpc->iomap.bdev);
1185	bio->bi_iter.bi_sector = sector;
1186	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
1187	bio->bi_write_hint = inode->i_write_hint;
1188	wbc_init_bio(wbc, bio);
1189
1190	ioend = container_of(bio, struct iomap_ioend, io_inline_bio);
1191	INIT_LIST_HEAD(&ioend->io_list);
1192	ioend->io_type = wpc->iomap.type;
1193	ioend->io_flags = wpc->iomap.flags;
1194	ioend->io_inode = inode;
1195	ioend->io_size = 0;
1196	ioend->io_offset = offset;
1197	ioend->io_bio = bio;
1198	return ioend;
1199}
1200
1201/*
1202 * Allocate a new bio, and chain the old bio to the new one.
1203 *
1204 * Note that we have to perform the chaining in this unintuitive order
1205 * so that the bi_private linkage is set up in the right direction for the
1206 * traversal in iomap_finish_ioend().
1207 */
1208static struct bio *
1209iomap_chain_bio(struct bio *prev)
1210{
1211	struct bio *new;
1212
1213	new = bio_alloc(GFP_NOFS, BIO_MAX_VECS);
1214	bio_copy_dev(new, prev);/* also copies over blkcg information */
1215	new->bi_iter.bi_sector = bio_end_sector(prev);
1216	new->bi_opf = prev->bi_opf;
1217	new->bi_write_hint = prev->bi_write_hint;
1218
1219	bio_chain(prev, new);
1220	bio_get(prev);		/* for iomap_finish_ioend */
1221	submit_bio(prev);
1222	return new;
1223}
1224
1225static bool
1226iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t offset,
1227		sector_t sector)
1228{
1229	if ((wpc->iomap.flags & IOMAP_F_SHARED) !=
1230	    (wpc->ioend->io_flags & IOMAP_F_SHARED))
1231		return false;
1232	if (wpc->iomap.type != wpc->ioend->io_type)
1233		return false;
1234	if (offset != wpc->ioend->io_offset + wpc->ioend->io_size)
1235		return false;
1236	if (sector != bio_end_sector(wpc->ioend->io_bio))
1237		return false;
1238	return true;
1239}
1240
1241/*
1242 * Test to see if we have an existing ioend structure that we could append to
1243 * first; otherwise finish off the current ioend and start another.
1244 */
1245static void
1246iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
1247		struct iomap_page *iop, struct iomap_writepage_ctx *wpc,
1248		struct writeback_control *wbc, struct list_head *iolist)
1249{
1250	sector_t sector = iomap_sector(&wpc->iomap, offset);
1251	unsigned len = i_blocksize(inode);
1252	unsigned poff = offset & (PAGE_SIZE - 1);
1253
1254	if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, offset, sector)) {
1255		if (wpc->ioend)
1256			list_add(&wpc->ioend->io_list, iolist);
1257		wpc->ioend = iomap_alloc_ioend(inode, wpc, offset, sector, wbc);
1258	}
1259
1260	if (bio_add_page(wpc->ioend->io_bio, page, len, poff) != len) {
1261		wpc->ioend->io_bio = iomap_chain_bio(wpc->ioend->io_bio);
1262		__bio_add_page(wpc->ioend->io_bio, page, len, poff);
1263	}
1264
1265	if (iop)
1266		atomic_add(len, &iop->write_bytes_pending);
1267	wpc->ioend->io_size += len;
1268	wbc_account_cgroup_owner(wbc, page, len);
1269}
1270
1271/*
1272 * We implement an immediate ioend submission policy here to avoid needing to
1273 * chain multiple ioends and hence nest mempool allocations which can violate
1274 * the forward progress guarantees we need to provide. The current ioend we're
1275 * adding blocks to is cached in the writepage context, and if the new block
1276 * doesn't append to the cached ioend, it will create a new ioend and cache that
1277 * instead.
1278 *
1279 * If a new ioend is created and cached, the old ioend is returned and queued
1280 * locally for submission once the entire page is processed or an error has been
1281 * detected.  While ioends are submitted immediately after they are completed,
1282 * batching optimisations are provided by higher level block plugging.
1283 *
1284 * At the end of a writeback pass, there will be a cached ioend remaining on the
1285 * writepage context that the caller will need to submit.
1286 */
1287static int
1288iomap_writepage_map(struct iomap_writepage_ctx *wpc,
1289		struct writeback_control *wbc, struct inode *inode,
1290		struct page *page, u64 end_offset)
1291{
1292	struct iomap_page *iop = iomap_page_create(inode, page);
1293	struct iomap_ioend *ioend, *next;
1294	unsigned len = i_blocksize(inode);
1295	u64 file_offset; /* file offset of page */
1296	int error = 0, count = 0, i;
1297	LIST_HEAD(submit_list);
1298
1299	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
1300
1301	/*
1302	 * Walk through the page to find areas to write back. If we run off the
1303	 * end of the current map or find the current map invalid, grab a new
1304	 * one.
1305	 */
1306	for (i = 0, file_offset = page_offset(page);
1307	     i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
1308	     i++, file_offset += len) {
1309		if (iop && !test_bit(i, iop->uptodate))
1310			continue;
1311
1312		error = wpc->ops->map_blocks(wpc, inode, file_offset);
1313		if (error)
1314			break;
1315		if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
1316			continue;
1317		if (wpc->iomap.type == IOMAP_HOLE)
1318			continue;
1319		iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
1320				 &submit_list);
1321		count++;
1322	}
1323
1324	WARN_ON_ONCE(!wpc->ioend && !list_empty(&submit_list));
1325	WARN_ON_ONCE(!PageLocked(page));
1326	WARN_ON_ONCE(PageWriteback(page));
1327	WARN_ON_ONCE(PageDirty(page));
1328
1329	/*
1330	 * We cannot cancel the ioend directly here on error.  We may have
1331	 * already set other pages under writeback and hence we have to run I/O
1332	 * completion to mark the error state of the pages under writeback
1333	 * appropriately.
1334	 */
1335	if (unlikely(error)) {
1336		/*
1337		 * Let the filesystem know what portion of the current page
1338		 * failed to map. If the page hasn't been added to ioend, it
1339		 * won't be affected by I/O completion and we must unlock it
1340		 * now.
1341		 */
1342		if (wpc->ops->discard_page)
1343			wpc->ops->discard_page(page, file_offset);
1344		if (!count) {
1345			ClearPageUptodate(page);
1346			unlock_page(page);
1347			goto done;
1348		}
1349	}
1350
1351	set_page_writeback(page);
1352	unlock_page(page);
1353
1354	/*
1355	 * Preserve the original error if there was one; catch
1356	 * submission errors here and propagate into subsequent ioend
1357	 * submissions.
1358	 */
1359	list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
1360		int error2;
1361
1362		list_del_init(&ioend->io_list);
1363		error2 = iomap_submit_ioend(wpc, ioend, error);
1364		if (error2 && !error)
1365			error = error2;
1366	}
1367
1368	/*
1369	 * We can end up here with no error and nothing to write only if we race
1370	 * with a partial page truncate on a sub-page block sized filesystem.
1371	 */
1372	if (!count)
1373		end_page_writeback(page);
1374done:
1375	mapping_set_error(page->mapping, error);
1376	return error;
1377}
1378
1379/*
1380 * Write out a dirty page.
1381 *
1382 * For delalloc space on the page, we need to allocate space and flush it.
1383 * For unwritten space on the page, we need to start the conversion to
1384 * regular allocated space.
1385 */
1386static int
1387iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
1388{
1389	struct iomap_writepage_ctx *wpc = data;
1390	struct inode *inode = page->mapping->host;
1391	pgoff_t end_index;
1392	u64 end_offset;
1393	loff_t offset;
1394
1395	trace_iomap_writepage(inode, page_offset(page), PAGE_SIZE);
1396
1397	/*
1398	 * Refuse to write the page out if we're called from reclaim context.
1399	 *
1400	 * This avoids stack overflows when called from deeply used stacks in
1401	 * random callers for direct reclaim or memcg reclaim.  We explicitly
1402	 * allow reclaim from kswapd as the stack usage there is relatively low.
1403	 *
1404	 * This should never happen except in the case of a VM regression so
1405	 * warn about it.
1406	 */
1407	if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
1408			PF_MEMALLOC))
1409		goto redirty;
1410
1411	/*
1412	 * Is this page beyond the end of the file?
1413	 *
1414	 * The page index is less than the end_index, adjust the end_offset
1415	 * to the highest offset that this page should represent.
1416	 * -----------------------------------------------------
1417	 * |			file mapping	       | <EOF> |
1418	 * -----------------------------------------------------
1419	 * | Page ... | Page N-2 | Page N-1 |  Page N  |       |
1420	 * ^--------------------------------^----------|--------
1421	 * |     desired writeback range    |      see else    |
1422	 * ---------------------------------^------------------|
1423	 */
1424	offset = i_size_read(inode);
1425	end_index = offset >> PAGE_SHIFT;
1426	if (page->index < end_index)
1427		end_offset = (loff_t)(page->index + 1) << PAGE_SHIFT;
1428	else {
1429		/*
1430		 * Check whether the page to write out is beyond or straddles
1431		 * i_size or not.
1432		 * -------------------------------------------------------
1433		 * |		file mapping		        | <EOF>  |
1434		 * -------------------------------------------------------
1435		 * | Page ... | Page N-2 | Page N-1 |  Page N   | Beyond |
1436		 * ^--------------------------------^-----------|---------
1437		 * |				    |      Straddles     |
1438		 * ---------------------------------^-----------|--------|
1439		 */
1440		unsigned offset_into_page = offset & (PAGE_SIZE - 1);
1441
1442		/*
1443		 * Skip the page if it's fully outside i_size, e.g. due to a
1444		 * truncate operation that's in progress. We must redirty the
1445		 * page so that reclaim stops reclaiming it. Otherwise
1446		 * iomap_vm_releasepage() is called on it and gets confused.
1447		 *
1448		 * Note that the end_index is unsigned long.  If the given
1449		 * offset is greater than 16TB on a 32-bit system then if we
1450		 * checked if the page is fully outside i_size with
1451		 * "if (page->index >= end_index + 1)", "end_index + 1" would
1452		 * overflow and evaluate to 0.  Hence this page would be
1453		 * redirtied and written out repeatedly, which would result in
1454		 * an infinite loop; the user program performing this operation
1455		 * would hang.  Instead, we can detect this situation by
1456		 * checking if the page is totally beyond i_size or if its
1457		 * offset is just equal to the EOF.
1458		 */
1459		if (page->index > end_index ||
1460		    (page->index == end_index && offset_into_page == 0))
1461			goto redirty;
1462
1463		/*
1464		 * The page straddles i_size.  It must be zeroed out on each
1465		 * and every writepage invocation because it may be mmapped.
1466		 * "A file is mapped in multiples of the page size.  For a file
1467		 * that is not a multiple of the page size, the remaining
1468		 * memory is zeroed when mapped, and writes to that region are
1469		 * not written out to the file."
1470		 */
1471		zero_user_segment(page, offset_into_page, PAGE_SIZE);
1472
1473		/* Adjust the end_offset to the end of file */
1474		end_offset = offset;
1475	}
1476
1477	return iomap_writepage_map(wpc, wbc, inode, page, end_offset);
1478
1479redirty:
1480	redirty_page_for_writepage(wbc, page);
1481	unlock_page(page);
1482	return 0;
1483}
1484
1485int
1486iomap_writepage(struct page *page, struct writeback_control *wbc,
1487		struct iomap_writepage_ctx *wpc,
1488		const struct iomap_writeback_ops *ops)
1489{
1490	int ret;
1491
1492	wpc->ops = ops;
1493	ret = iomap_do_writepage(page, wbc, wpc);
1494	if (!wpc->ioend)
1495		return ret;
1496	return iomap_submit_ioend(wpc, wpc->ioend, ret);
1497}
1498EXPORT_SYMBOL_GPL(iomap_writepage);
1499
1500int
1501iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
1502		struct iomap_writepage_ctx *wpc,
1503		const struct iomap_writeback_ops *ops)
1504{
1505	int			ret;
1506
1507	wpc->ops = ops;
1508	ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
1509	if (!wpc->ioend)
1510		return ret;
1511	return iomap_submit_ioend(wpc, wpc->ioend, ret);
1512}
1513EXPORT_SYMBOL_GPL(iomap_writepages);
1514
1515static int __init iomap_init(void)
1516{
1517	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
1518			   offsetof(struct iomap_ioend, io_inline_bio),
1519			   BIOSET_NEED_BVECS);
1520}
1521fs_initcall(iomap_init);
1522