bcachefs: Split up fs-io.[ch]

fs-io.c is too big - time for some reorganization
 - fs-dio.c: direct io
 - fs-pagecache.c: pagecache data structures (bch_folio), utility code

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 1098 insertions, 0 deletions

diff --git a/fs/bcachefs/fs-io-buffered.c b/fs/bcachefs/fs-io-buffered.c
new file mode 100644
index 000000000000..102c70887f76
--- /dev/null
+++ b/fs/bcachefs/fs-io-buffered.c
@@ -0,0 +1,1098 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef NO_BCACHEFS_FS
+
+#include "bcachefs.h"
+#include "alloc_foreground.h"
+#include "bkey_buf.h"
+#include "fs-io.h"
+#include "fs-io-buffered.h"
+#include "fs-io-direct.h"
+#include "fs-io-pagecache.h"
+#include "io.h"
+
+#include <linux/backing-dev.h>
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+
+static inline bool bio_full(struct bio *bio, unsigned len)
+{
+	if (bio->bi_vcnt >= bio->bi_max_vecs)
+		return true;
+	if (bio->bi_iter.bi_size > UINT_MAX - len)
+		return true;
+	return false;
+}
+
+/* readpage(s): */
+
+static void bch2_readpages_end_io(struct bio *bio)
+{
+	struct folio_iter fi;
+
+	bio_for_each_folio_all(fi, bio) {
+		if (!bio->bi_status) {
+			folio_mark_uptodate(fi.folio);
+		} else {
+			folio_clear_uptodate(fi.folio);
+			folio_set_error(fi.folio);
+		}
+		folio_unlock(fi.folio);
+	}
+
+	bio_put(bio);
+}
+
+struct readpages_iter {
+	struct address_space	*mapping;
+	unsigned		idx;
+	folios			folios;
+};
+
+static int readpages_iter_init(struct readpages_iter *iter,
+			       struct readahead_control *ractl)
+{
+	struct folio **fi;
+	int ret;
+
+	memset(iter, 0, sizeof(*iter));
+
+	iter->mapping = ractl->mapping;
+
+	ret = bch2_filemap_get_contig_folios_d(iter->mapping,
+				ractl->_index << PAGE_SHIFT,
+				(ractl->_index + ractl->_nr_pages) << PAGE_SHIFT,
+				0, mapping_gfp_mask(iter->mapping),
+				&iter->folios);
+	if (ret)
+		return ret;
+
+	darray_for_each(iter->folios, fi) {
+		ractl->_nr_pages -= 1U << folio_order(*fi);
+		__bch2_folio_create(*fi, __GFP_NOFAIL|GFP_KERNEL);
+		folio_put(*fi);
+		folio_put(*fi);
+	}
+
+	return 0;
+}
+
+static inline struct folio *readpage_iter_peek(struct readpages_iter *iter)
+{
+	if (iter->idx >= iter->folios.nr)
+		return NULL;
+	return iter->folios.data[iter->idx];
+}
+
+static inline void readpage_iter_advance(struct readpages_iter *iter)
+{
+	iter->idx++;
+}
+
+static bool extent_partial_reads_expensive(struct bkey_s_c k)
+{
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	struct bch_extent_crc_unpacked crc;
+	const union bch_extent_entry *i;
+
+	bkey_for_each_crc(k.k, ptrs, crc, i)
+		if (crc.csum_type || crc.compression_type)
+			return true;
+	return false;
+}
+
+static int readpage_bio_extend(struct btree_trans *trans,
+			       struct readpages_iter *iter,
+			       struct bio *bio,
+			       unsigned sectors_this_extent,
+			       bool get_more)
+{
+	/* Don't hold btree locks while allocating memory: */
+	bch2_trans_unlock(trans);
+
+	while (bio_sectors(bio) < sectors_this_extent &&
+	       bio->bi_vcnt < bio->bi_max_vecs) {
+		struct folio *folio = readpage_iter_peek(iter);
+		int ret;
+
+		if (folio) {
+			readpage_iter_advance(iter);
+		} else {
+			pgoff_t folio_offset = bio_end_sector(bio) >> PAGE_SECTORS_SHIFT;
+
+			if (!get_more)
+				break;
+
+			folio = xa_load(&iter->mapping->i_pages, folio_offset);
+			if (folio && !xa_is_value(folio))
+				break;
+
+			folio = filemap_alloc_folio(readahead_gfp_mask(iter->mapping), 0);
+			if (!folio)
+				break;
+
+			if (!__bch2_folio_create(folio, GFP_KERNEL)) {
+				folio_put(folio);
+				break;
+			}
+
+			ret = filemap_add_folio(iter->mapping, folio, folio_offset, GFP_KERNEL);
+			if (ret) {
+				__bch2_folio_release(folio);
+				folio_put(folio);
+				break;
+			}
+
+			folio_put(folio);
+		}
+
+		BUG_ON(folio_sector(folio) != bio_end_sector(bio));
+
+		BUG_ON(!bio_add_folio(bio, folio, folio_size(folio), 0));
+	}
+
+	return bch2_trans_relock(trans);
+}
+
+static void bchfs_read(struct btree_trans *trans,
+		       struct bch_read_bio *rbio,
+		       subvol_inum inum,
+		       struct readpages_iter *readpages_iter)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_buf sk;
+	int flags = BCH_READ_RETRY_IF_STALE|
+		BCH_READ_MAY_PROMOTE;
+	u32 snapshot;
+	int ret = 0;
+
+	rbio->c = c;
+	rbio->start_time = local_clock();
+	rbio->subvol = inum.subvol;
+
+	bch2_bkey_buf_init(&sk);
+retry:
+	bch2_trans_begin(trans);
+	iter = (struct btree_iter) { NULL };
+
+	ret = bch2_subvolume_get_snapshot(trans, inum.subvol, &snapshot);
+	if (ret)
+		goto err;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_extents,
+			     SPOS(inum.inum, rbio->bio.bi_iter.bi_sector, snapshot),
+			     BTREE_ITER_SLOTS);
+	while (1) {
+		struct bkey_s_c k;
+		unsigned bytes, sectors, offset_into_extent;
+		enum btree_id data_btree = BTREE_ID_extents;
+
+		/*
+		 * read_extent -> io_time_reset may cause a transaction restart
+		 * without returning an error, we need to check for that here:
+		 */
+		ret = bch2_trans_relock(trans);
+		if (ret)
+			break;
+
+		bch2_btree_iter_set_pos(&iter,
+				POS(inum.inum, rbio->bio.bi_iter.bi_sector));
+
+		k = bch2_btree_iter_peek_slot(&iter);
+		ret = bkey_err(k);
+		if (ret)
+			break;
+
+		offset_into_extent = iter.pos.offset -
+			bkey_start_offset(k.k);
+		sectors = k.k->size - offset_into_extent;
+
+		bch2_bkey_buf_reassemble(&sk, c, k);
+
+		ret = bch2_read_indirect_extent(trans, &data_btree,
+					&offset_into_extent, &sk);
+		if (ret)
+			break;
+
+		k = bkey_i_to_s_c(sk.k);
+
+		sectors = min(sectors, k.k->size - offset_into_extent);
+
+		if (readpages_iter) {
+			ret = readpage_bio_extend(trans, readpages_iter, &rbio->bio, sectors,
+						  extent_partial_reads_expensive(k));
+			if (ret)
+				break;
+		}
+
+		bytes = min(sectors, bio_sectors(&rbio->bio)) << 9;
+		swap(rbio->bio.bi_iter.bi_size, bytes);
+
+		if (rbio->bio.bi_iter.bi_size == bytes)
+			flags |= BCH_READ_LAST_FRAGMENT;
+
+		bch2_bio_page_state_set(&rbio->bio, k);
+
+		bch2_read_extent(trans, rbio, iter.pos,
+				 data_btree, k, offset_into_extent, flags);
+
+		if (flags & BCH_READ_LAST_FRAGMENT)
+			break;
+
+		swap(rbio->bio.bi_iter.bi_size, bytes);
+		bio_advance(&rbio->bio, bytes);
+
+		ret = btree_trans_too_many_iters(trans);
+		if (ret)
+			break;
+	}
+err:
+	bch2_trans_iter_exit(trans, &iter);
+
+	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
+		goto retry;
+
+	if (ret) {
+		bch_err_inum_offset_ratelimited(c,
+				iter.pos.inode,
+				iter.pos.offset << 9,
+				"read error %i from btree lookup", ret);
+		rbio->bio.bi_status = BLK_STS_IOERR;
+		bio_endio(&rbio->bio);
+	}
+
+	bch2_bkey_buf_exit(&sk, c);
+}
+
+void bch2_readahead(struct readahead_control *ractl)
+{
+	struct bch_inode_info *inode = to_bch_ei(ractl->mapping->host);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch_io_opts opts;
+	struct btree_trans trans;
+	struct folio *folio;
+	struct readpages_iter readpages_iter;
+	int ret;
+
+	bch2_inode_opts_get(&opts, c, &inode->ei_inode);
+
+	ret = readpages_iter_init(&readpages_iter, ractl);
+	BUG_ON(ret);
+
+	bch2_trans_init(&trans, c, 0, 0);
+
+	bch2_pagecache_add_get(inode);
+
+	while ((folio = readpage_iter_peek(&readpages_iter))) {
+		unsigned n = min_t(unsigned,
+				   readpages_iter.folios.nr -
+				   readpages_iter.idx,
+				   BIO_MAX_VECS);
+		struct bch_read_bio *rbio =
+			rbio_init(bio_alloc_bioset(NULL, n, REQ_OP_READ,
+						   GFP_KERNEL, &c->bio_read),
+				  opts);
+
+		readpage_iter_advance(&readpages_iter);
+
+		rbio->bio.bi_iter.bi_sector = folio_sector(folio);
+		rbio->bio.bi_end_io = bch2_readpages_end_io;
+		BUG_ON(!bio_add_folio(&rbio->bio, folio, folio_size(folio), 0));
+
+		bchfs_read(&trans, rbio, inode_inum(inode),
+			   &readpages_iter);
+		bch2_trans_unlock(&trans);
+	}
+
+	bch2_pagecache_add_put(inode);
+
+	bch2_trans_exit(&trans);
+	darray_exit(&readpages_iter.folios);
+}
+
+static void __bchfs_readfolio(struct bch_fs *c, struct bch_read_bio *rbio,
+			     subvol_inum inum, struct folio *folio)
+{
+	struct btree_trans trans;
+
+	bch2_folio_create(folio, __GFP_NOFAIL);
+
+	rbio->bio.bi_opf = REQ_OP_READ|REQ_SYNC;
+	rbio->bio.bi_iter.bi_sector = folio_sector(folio);
+	BUG_ON(!bio_add_folio(&rbio->bio, folio, folio_size(folio), 0));
+
+	bch2_trans_init(&trans, c, 0, 0);
+	bchfs_read(&trans, rbio, inum, NULL);
+	bch2_trans_exit(&trans);
+}
+
+static void bch2_read_single_folio_end_io(struct bio *bio)
+{
+	complete(bio->bi_private);
+}
+
+int bch2_read_single_folio(struct folio *folio, struct address_space *mapping)
+{
+	struct bch_inode_info *inode = to_bch_ei(mapping->host);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch_read_bio *rbio;
+	struct bch_io_opts opts;
+	int ret;
+	DECLARE_COMPLETION_ONSTACK(done);
+
+	bch2_inode_opts_get(&opts, c, &inode->ei_inode);
+
+	rbio = rbio_init(bio_alloc_bioset(NULL, 1, REQ_OP_READ, GFP_KERNEL, &c->bio_read),
+			 opts);
+	rbio->bio.bi_private = &done;
+	rbio->bio.bi_end_io = bch2_read_single_folio_end_io;
+
+	__bchfs_readfolio(c, rbio, inode_inum(inode), folio);
+	wait_for_completion(&done);
+
+	ret = blk_status_to_errno(rbio->bio.bi_status);
+	bio_put(&rbio->bio);
+
+	if (ret < 0)
+		return ret;
+
+	folio_mark_uptodate(folio);
+	return 0;
+}
+
+int bch2_read_folio(struct file *file, struct folio *folio)
+{
+	int ret;
+
+	ret = bch2_read_single_folio(folio, folio->mapping);
+	folio_unlock(folio);
+	return bch2_err_class(ret);
+}
+
+/* writepages: */
+
+struct bch_writepage_io {
+	struct bch_inode_info		*inode;
+
+	/* must be last: */
+	struct bch_write_op		op;
+};
+
+struct bch_writepage_state {
+	struct bch_writepage_io	*io;
+	struct bch_io_opts	opts;
+	struct bch_folio_sector	*tmp;
+	unsigned		tmp_sectors;
+};
+
+static inline struct bch_writepage_state bch_writepage_state_init(struct bch_fs *c,
+								  struct bch_inode_info *inode)
+{
+	struct bch_writepage_state ret = { 0 };
+
+	bch2_inode_opts_get(&ret.opts, c, &inode->ei_inode);
+	return ret;
+}
+
+static void bch2_writepage_io_done(struct bch_write_op *op)
+{
+	struct bch_writepage_io *io =
+		container_of(op, struct bch_writepage_io, op);
+	struct bch_fs *c = io->op.c;
+	struct bio *bio = &io->op.wbio.bio;
+	struct folio_iter fi;
+	unsigned i;
+
+	if (io->op.error) {
+		set_bit(EI_INODE_ERROR, &io->inode->ei_flags);
+
+		bio_for_each_folio_all(fi, bio) {
+			struct bch_folio *s;
+
+			folio_set_error(fi.folio);
+			mapping_set_error(fi.folio->mapping, -EIO);
+
+			s = __bch2_folio(fi.folio);
+			spin_lock(&s->lock);
+			for (i = 0; i < folio_sectors(fi.folio); i++)
+				s->s[i].nr_replicas = 0;
+			spin_unlock(&s->lock);
+		}
+	}
+
+	if (io->op.flags & BCH_WRITE_WROTE_DATA_INLINE) {
+		bio_for_each_folio_all(fi, bio) {
+			struct bch_folio *s;
+
+			s = __bch2_folio(fi.folio);
+			spin_lock(&s->lock);
+			for (i = 0; i < folio_sectors(fi.folio); i++)
+				s->s[i].nr_replicas = 0;
+			spin_unlock(&s->lock);
+		}
+	}
+
+	/*
+	 * racing with fallocate can cause us to add fewer sectors than
+	 * expected - but we shouldn't add more sectors than expected:
+	 */
+	WARN_ON_ONCE(io->op.i_sectors_delta > 0);
+
+	/*
+	 * (error (due to going RO) halfway through a page can screw that up
+	 * slightly)
+	 * XXX wtf?
+	   BUG_ON(io->op.op.i_sectors_delta >= PAGE_SECTORS);
+	 */
+
+	/*
+	 * PageWriteback is effectively our ref on the inode - fixup i_blocks
+	 * before calling end_page_writeback:
+	 */
+	bch2_i_sectors_acct(c, io->inode, NULL, io->op.i_sectors_delta);
+
+	bio_for_each_folio_all(fi, bio) {
+		struct bch_folio *s = __bch2_folio(fi.folio);
+
+		if (atomic_dec_and_test(&s->write_count))
+			folio_end_writeback(fi.folio);
+	}
+
+	bio_put(&io->op.wbio.bio);
+}
+
+static void bch2_writepage_do_io(struct bch_writepage_state *w)
+{
+	struct bch_writepage_io *io = w->io;
+
+	w->io = NULL;
+	closure_call(&io->op.cl, bch2_write, NULL, NULL);
+}
+
+/*
+ * Get a bch_writepage_io and add @page to it - appending to an existing one if
+ * possible, else allocating a new one:
+ */
+static void bch2_writepage_io_alloc(struct bch_fs *c,
+				    struct writeback_control *wbc,
+				    struct bch_writepage_state *w,
+				    struct bch_inode_info *inode,
+				    u64 sector,
+				    unsigned nr_replicas)
+{
+	struct bch_write_op *op;
+
+	w->io = container_of(bio_alloc_bioset(NULL, BIO_MAX_VECS,
+					      REQ_OP_WRITE,
+					      GFP_KERNEL,
+					      &c->writepage_bioset),
+			     struct bch_writepage_io, op.wbio.bio);
+
+	w->io->inode		= inode;
+	op			= &w->io->op;
+	bch2_write_op_init(op, c, w->opts);
+	op->target		= w->opts.foreground_target;
+	op->nr_replicas		= nr_replicas;
+	op->res.nr_replicas	= nr_replicas;
+	op->write_point		= writepoint_hashed(inode->ei_last_dirtied);
+	op->subvol		= inode->ei_subvol;
+	op->pos			= POS(inode->v.i_ino, sector);
+	op->end_io		= bch2_writepage_io_done;
+	op->devs_need_flush	= &inode->ei_devs_need_flush;
+	op->wbio.bio.bi_iter.bi_sector = sector;
+	op->wbio.bio.bi_opf	= wbc_to_write_flags(wbc);
+}
+
+static int __bch2_writepage(struct folio *folio,
+			    struct writeback_control *wbc,
+			    void *data)
+{
+	struct bch_inode_info *inode = to_bch_ei(folio->mapping->host);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch_writepage_state *w = data;
+	struct bch_folio *s;
+	unsigned i, offset, f_sectors, nr_replicas_this_write = U32_MAX;
+	loff_t i_size = i_size_read(&inode->v);
+	int ret;
+
+	EBUG_ON(!folio_test_uptodate(folio));
+
+	/* Is the folio fully inside i_size? */
+	if (folio_end_pos(folio) <= i_size)
+		goto do_io;
+
+	/* Is the folio fully outside i_size? (truncate in progress) */
+	if (folio_pos(folio) >= i_size) {
+		folio_unlock(folio);
+		return 0;
+	}
+
+	/*
+	 * The folio straddles i_size.  It must be zeroed out on each and every
+	 * writepage invocation because it may be mmapped.  "A file is mapped
+	 * in multiples of the folio size.  For a file that is not a multiple of
+	 * the  folio size, the remaining memory is zeroed when mapped, and
+	 * writes to that region are not written out to the file."
+	 */
+	folio_zero_segment(folio,
+			   i_size - folio_pos(folio),
+			   folio_size(folio));
+do_io:
+	f_sectors = folio_sectors(folio);
+	s = bch2_folio(folio);
+
+	if (f_sectors > w->tmp_sectors) {
+		kfree(w->tmp);
+		w->tmp = kcalloc(f_sectors, sizeof(struct bch_folio_sector), __GFP_NOFAIL);
+		w->tmp_sectors = f_sectors;
+	}
+
+	/*
+	 * Things get really hairy with errors during writeback:
+	 */
+	ret = bch2_get_folio_disk_reservation(c, inode, folio, false);
+	BUG_ON(ret);
+
+	/* Before unlocking the page, get copy of reservations: */
+	spin_lock(&s->lock);
+	memcpy(w->tmp, s->s, sizeof(struct bch_folio_sector) * f_sectors);
+
+	for (i = 0; i < f_sectors; i++) {
+		if (s->s[i].state < SECTOR_dirty)
+			continue;
+
+		nr_replicas_this_write =
+			min_t(unsigned, nr_replicas_this_write,
+			      s->s[i].nr_replicas +
+			      s->s[i].replicas_reserved);
+	}
+
+	for (i = 0; i < f_sectors; i++) {
+		if (s->s[i].state < SECTOR_dirty)
+			continue;
+
+		s->s[i].nr_replicas = w->opts.compression
+			? 0 : nr_replicas_this_write;
+
+		s->s[i].replicas_reserved = 0;
+		bch2_folio_sector_set(folio, s, i, SECTOR_allocated);
+	}
+	spin_unlock(&s->lock);
+
+	BUG_ON(atomic_read(&s->write_count));
+	atomic_set(&s->write_count, 1);
+
+	BUG_ON(folio_test_writeback(folio));
+	folio_start_writeback(folio);
+
+	folio_unlock(folio);
+
+	offset = 0;
+	while (1) {
+		unsigned sectors = 0, dirty_sectors = 0, reserved_sectors = 0;
+		u64 sector;
+
+		while (offset < f_sectors &&
+		       w->tmp[offset].state < SECTOR_dirty)
+			offset++;
+
+		if (offset == f_sectors)
+			break;
+
+		while (offset + sectors < f_sectors &&
+		       w->tmp[offset + sectors].state >= SECTOR_dirty) {
+			reserved_sectors += w->tmp[offset + sectors].replicas_reserved;
+			dirty_sectors += w->tmp[offset + sectors].state == SECTOR_dirty;
+			sectors++;
+		}
+		BUG_ON(!sectors);
+
+		sector = folio_sector(folio) + offset;
+
+		if (w->io &&
+		    (w->io->op.res.nr_replicas != nr_replicas_this_write ||
+		     bio_full(&w->io->op.wbio.bio, sectors << 9) ||
+		     w->io->op.wbio.bio.bi_iter.bi_size + (sectors << 9) >=
+		     (BIO_MAX_VECS * PAGE_SIZE) ||
+		     bio_end_sector(&w->io->op.wbio.bio) != sector))
+			bch2_writepage_do_io(w);
+
+		if (!w->io)
+			bch2_writepage_io_alloc(c, wbc, w, inode, sector,
+						nr_replicas_this_write);
+
+		atomic_inc(&s->write_count);
+
+		BUG_ON(inode != w->io->inode);
+		BUG_ON(!bio_add_folio(&w->io->op.wbio.bio, folio,
+				     sectors << 9, offset << 9));
+
+		/* Check for writing past i_size: */
+		WARN_ONCE((bio_end_sector(&w->io->op.wbio.bio) << 9) >
+			  round_up(i_size, block_bytes(c)) &&
+			  !test_bit(BCH_FS_EMERGENCY_RO, &c->flags),
+			  "writing past i_size: %llu > %llu (unrounded %llu)\n",
+			  bio_end_sector(&w->io->op.wbio.bio) << 9,
+			  round_up(i_size, block_bytes(c)),
+			  i_size);
+
+		w->io->op.res.sectors += reserved_sectors;
+		w->io->op.i_sectors_delta -= dirty_sectors;
+		w->io->op.new_i_size = i_size;
+
+		offset += sectors;
+	}
+
+	if (atomic_dec_and_test(&s->write_count))
+		folio_end_writeback(folio);
+
+	return 0;
+}
+
+int bch2_writepages(struct address_space *mapping, struct writeback_control *wbc)
+{
+	struct bch_fs *c = mapping->host->i_sb->s_fs_info;
+	struct bch_writepage_state w =
+		bch_writepage_state_init(c, to_bch_ei(mapping->host));
+	struct blk_plug plug;
+	int ret;
+
+	blk_start_plug(&plug);
+	ret = write_cache_pages(mapping, wbc, __bch2_writepage, &w);
+	if (w.io)
+		bch2_writepage_do_io(&w);
+	blk_finish_plug(&plug);
+	kfree(w.tmp);
+	return bch2_err_class(ret);
+}
+
+/* buffered writes: */
+
+int bch2_write_begin(struct file *file, struct address_space *mapping,
+		     loff_t pos, unsigned len,
+		     struct page **pagep, void **fsdata)
+{
+	struct bch_inode_info *inode = to_bch_ei(mapping->host);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch2_folio_reservation *res;
+	struct folio *folio;
+	unsigned offset;
+	int ret = -ENOMEM;
+
+	res = kmalloc(sizeof(*res), GFP_KERNEL);
+	if (!res)
+		return -ENOMEM;
+
+	bch2_folio_reservation_init(c, inode, res);
+	*fsdata = res;
+
+	bch2_pagecache_add_get(inode);
+
+	folio = __filemap_get_folio(mapping, pos >> PAGE_SHIFT,
+				FGP_LOCK|FGP_WRITE|FGP_CREAT|FGP_STABLE,
+				mapping_gfp_mask(mapping));
+	if (IS_ERR_OR_NULL(folio))
+		goto err_unlock;
+
+	if (folio_test_uptodate(folio))
+		goto out;
+
+	offset = pos - folio_pos(folio);
+	len = min_t(size_t, len, folio_end_pos(folio) - pos);
+
+	/* If we're writing entire folio, don't need to read it in first: */
+	if (!offset && len == folio_size(folio))
+		goto out;
+
+	if (!offset && pos + len >= inode->v.i_size) {
+		folio_zero_segment(folio, len, folio_size(folio));
+		flush_dcache_folio(folio);
+		goto out;
+	}
+
+	if (folio_pos(folio) >= inode->v.i_size) {
+		folio_zero_segments(folio, 0, offset, offset + len, folio_size(folio));
+		flush_dcache_folio(folio);
+		goto out;
+	}
+readpage:
+	ret = bch2_read_single_folio(folio, mapping);
+	if (ret)
+		goto err;
+out:
+	ret = bch2_folio_set(c, inode_inum(inode), &folio, 1);
+	if (ret)
+		goto err;
+
+	ret = bch2_folio_reservation_get(c, inode, folio, res, offset, len);
+	if (ret) {
+		if (!folio_test_uptodate(folio)) {
+			/*
+			 * If the folio hasn't been read in, we won't know if we
+			 * actually need a reservation - we don't actually need
+			 * to read here, we just need to check if the folio is
+			 * fully backed by uncompressed data:
+			 */
+			goto readpage;
+		}
+
+		goto err;
+	}
+
+	*pagep = &folio->page;
+	return 0;
+err:
+	folio_unlock(folio);
+	folio_put(folio);
+	*pagep = NULL;
+err_unlock:
+	bch2_pagecache_add_put(inode);
+	kfree(res);
+	*fsdata = NULL;
+	return bch2_err_class(ret);
+}
+
+int bch2_write_end(struct file *file, struct address_space *mapping,
+		   loff_t pos, unsigned len, unsigned copied,
+		   struct page *page, void *fsdata)
+{
+	struct bch_inode_info *inode = to_bch_ei(mapping->host);
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch2_folio_reservation *res = fsdata;
+	struct folio *folio = page_folio(page);
+	unsigned offset = pos - folio_pos(folio);
+
+	lockdep_assert_held(&inode->v.i_rwsem);
+	BUG_ON(offset + copied > folio_size(folio));
+
+	if (unlikely(copied < len && !folio_test_uptodate(folio))) {
+		/*
+		 * The folio needs to be read in, but that would destroy
+		 * our partial write - simplest thing is to just force
+		 * userspace to redo the write:
+		 */
+		folio_zero_range(folio, 0, folio_size(folio));
+		flush_dcache_folio(folio);
+		copied = 0;
+	}
+
+	spin_lock(&inode->v.i_lock);
+	if (pos + copied > inode->v.i_size)
+		i_size_write(&inode->v, pos + copied);
+	spin_unlock(&inode->v.i_lock);
+
+	if (copied) {
+		if (!folio_test_uptodate(folio))
+			folio_mark_uptodate(folio);
+
+		bch2_set_folio_dirty(c, inode, folio, res, offset, copied);
+
+		inode->ei_last_dirtied = (unsigned long) current;
+	}
+
+	folio_unlock(folio);
+	folio_put(folio);
+	bch2_pagecache_add_put(inode);
+
+	bch2_folio_reservation_put(c, inode, res);
+	kfree(res);
+
+	return copied;
+}
+
+static noinline void folios_trunc(folios *folios, struct folio **fi)
+{
+	while (folios->data + folios->nr > fi) {
+		struct folio *f = darray_pop(folios);
+
+		folio_unlock(f);
+		folio_put(f);
+	}
+}
+
+static int __bch2_buffered_write(struct bch_inode_info *inode,
+				 struct address_space *mapping,
+				 struct iov_iter *iter,
+				 loff_t pos, unsigned len)
+{
+	struct bch_fs *c = inode->v.i_sb->s_fs_info;
+	struct bch2_folio_reservation res;
+	folios folios;
+	struct folio **fi, *f;
+	unsigned copied = 0, f_offset;
+	u64 end = pos + len, f_pos;
+	loff_t last_folio_pos = inode->v.i_size;
+	int ret = 0;
+
+	BUG_ON(!len);
+
+	bch2_folio_reservation_init(c, inode, &res);
+	darray_init(&folios);
+
+	ret = bch2_filemap_get_contig_folios_d(mapping, pos, end,
+				   FGP_LOCK|FGP_WRITE|FGP_STABLE|FGP_CREAT,
+				   mapping_gfp_mask(mapping),
+				   &folios);
+	if (ret)
+		goto out;
+
+	BUG_ON(!folios.nr);
+
+	f = darray_first(folios);
+	if (pos != folio_pos(f) && !folio_test_uptodate(f)) {
+		ret = bch2_read_single_folio(f, mapping);
+		if (ret)
+			goto out;
+	}
+
+	f = darray_last(folios);
+	end = min(end, folio_end_pos(f));
+	last_folio_pos = folio_pos(f);
+	if (end != folio_end_pos(f) && !folio_test_uptodate(f)) {
+		if (end >= inode->v.i_size) {
+			folio_zero_range(f, 0, folio_size(f));
+		} else {
+			ret = bch2_read_single_folio(f, mapping);
+			if (ret)
+				goto out;
+		}
+	}
+
+	ret = bch2_folio_set(c, inode_inum(inode), folios.data, folios.nr);
+	if (ret)
+		goto out;
+
+	f_pos = pos;
+	f_offset = pos - folio_pos(darray_first(folios));
+	darray_for_each(folios, fi) {
+		struct folio *f = *fi;
+		u64 f_len = min(end, folio_end_pos(f)) - f_pos;
+
+		/*
+		 * XXX: per POSIX and fstests generic/275, on -ENOSPC we're
+		 * supposed to write as much as we have disk space for.
+		 *
+		 * On failure here we should still write out a partial page if
+		 * we aren't completely out of disk space - we don't do that
+		 * yet:
+		 */
+		ret = bch2_folio_reservation_get(c, inode, f, &res, f_offset, f_len);
+		if (unlikely(ret)) {
+			folios_trunc(&folios, fi);
+			if (!folios.nr)
+				goto out;
+
+			end = min(end, folio_end_pos(darray_last(folios)));
+			break;
+		}
+
+		f_pos = folio_end_pos(f);
+		f_offset = 0;
+	}
+
+	if (mapping_writably_mapped(mapping))
+		darray_for_each(folios, fi)
+			flush_dcache_folio(*fi);
+
+	f_pos = pos;
+	f_offset = pos - folio_pos(darray_first(folios));
+	darray_for_each(folios, fi) {
+		struct folio *f = *fi;
+		u64 f_len = min(end, folio_end_pos(f)) - f_pos;
+		unsigned f_copied = copy_page_from_iter_atomic(&f->page, f_offset, f_len, iter);
+
+		if (!f_copied) {
+			folios_trunc(&folios, fi);
+			break;
+		}
+
+		if (!folio_test_uptodate(f) &&
+		    f_copied != folio_size(f) &&
+		    pos + copied + f_copied < inode->v.i_size) {
+			folio_zero_range(f, 0, folio_size(f));
+			folios_trunc(&folios, fi);
+			break;
+		}
+
+		flush_dcache_folio(f);
+		copied += f_copied;
+
+		if (f_copied != f_len) {
+			folios_trunc(&folios, fi + 1);
+			break;
+		}
+
+		f_pos = folio_end_pos(f);
+		f_offset = 0;
+	}
+
+	if (!copied)
+		goto out;
+
+	end = pos + copied;
+
+	spin_lock(&inode->v.i_lock);
+	if (end > inode->v.i_size)
+		i_size_write(&inode->v, end);
+	spin_unlock(&inode->v.i_lock);
+
+	f_pos = pos;
+	f_offset = pos - folio_pos(darray_first(folios));
+	darray_for_each(folios, fi) {
+		struct folio *f = *fi;
+		u64 f_len = min(end, folio_end_pos(f)) - f_pos;
+
+		if (!folio_test_uptodate(f))
+			folio_mark_uptodate(f);
+
+		bch2_set_folio_dirty(c, inode, f, &res, f_offset, f_len);
+
+		f_pos = folio_end_pos(f);
+		f_offset = 0;
+	}
+
+	inode->ei_last_dirtied = (unsigned long) current;
+out:
+	darray_for_each(folios, fi) {
+		folio_unlock(*fi);
+		folio_put(*fi);
+	}
+
+	/*
+	 * If the last folio added to the mapping starts beyond current EOF, we
+	 * performed a short write but left around at least one post-EOF folio.
+	 * Clean up the mapping before we return.
+	 */
+	if (last_folio_pos >= inode->v.i_size)
+		truncate_pagecache(&inode->v, inode->v.i_size);
+
+	darray_exit(&folios);
+	bch2_folio_reservation_put(c, inode, &res);
+
+	return copied ?: ret;
+}
+
+static ssize_t bch2_buffered_write(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct bch_inode_info *inode = file_bch_inode(file);
+	loff_t pos = iocb->ki_pos;
+	ssize_t written = 0;
+	int ret = 0;
+
+	bch2_pagecache_add_get(inode);
+
+	do {
+		unsigned offset = pos & (PAGE_SIZE - 1);
+		unsigned bytes = iov_iter_count(iter);
+again:
+		/*
+		 * Bring in the user page that we will copy from _first_.
+		 * Otherwise there's a nasty deadlock on copying from the
+		 * same page as we're writing to, without it being marked
+		 * up-to-date.
+		 *
+		 * Not only is this an optimisation, but it is also required
+		 * to check that the address is actually valid, when atomic
+		 * usercopies are used, below.
+		 */
+		if (unlikely(fault_in_iov_iter_readable(iter, bytes))) {
+			bytes = min_t(unsigned long, iov_iter_count(iter),
+				      PAGE_SIZE - offset);
+
+			if (unlikely(fault_in_iov_iter_readable(iter, bytes))) {
+				ret = -EFAULT;
+				break;
+			}
+		}
+
+		if (unlikely(fatal_signal_pending(current))) {
+			ret = -EINTR;
+			break;
+		}
+
+		ret = __bch2_buffered_write(inode, mapping, iter, pos, bytes);
+		if (unlikely(ret < 0))
+			break;
+
+		cond_resched();
+
+		if (unlikely(ret == 0)) {
+			/*
+			 * If we were unable to copy any data at all, we must
+			 * fall back to a single segment length write.
+			 *
+			 * If we didn't fallback here, we could livelock
+			 * because not all segments in the iov can be copied at
+			 * once without a pagefault.
+			 */
+			bytes = min_t(unsigned long, PAGE_SIZE - offset,
+				      iov_iter_single_seg_count(iter));
+			goto again;
+		}
+		pos += ret;
+		written += ret;
+		ret = 0;
+
+		balance_dirty_pages_ratelimited(mapping);
+	} while (iov_iter_count(iter));
+
+	bch2_pagecache_add_put(inode);
+
+	return written ? written : ret;
+}
+
+ssize_t bch2_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct bch_inode_info *inode = file_bch_inode(file);
+	ssize_t ret;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		ret = bch2_direct_write(iocb, from);
+		goto out;
+	}
+
+	inode_lock(&inode->v);
+
+	ret = generic_write_checks(iocb, from);
+	if (ret <= 0)
+		goto unlock;
+
+	ret = file_remove_privs(file);
+	if (ret)
+		goto unlock;
+
+	ret = file_update_time(file);
+	if (ret)
+		goto unlock;
+
+	ret = bch2_buffered_write(iocb, from);
+	if (likely(ret > 0))
+		iocb->ki_pos += ret;
+unlock:
+	inode_unlock(&inode->v);
+
+	if (ret > 0)
+		ret = generic_write_sync(iocb, ret);
+out:
+	return bch2_err_class(ret);
+}
+
+void bch2_fs_fs_io_buffered_exit(struct bch_fs *c)
+{
+	bioset_exit(&c->writepage_bioset);
+}
+
+int bch2_fs_fs_io_buffered_init(struct bch_fs *c)
+{
+	if (bioset_init(&c->writepage_bioset,
+			4, offsetof(struct bch_writepage_io, op.wbio.bio),
+			BIOSET_NEED_BVECS))
+		return -BCH_ERR_ENOMEM_writepage_bioset_init;
+
+	return 0;
+}
+
+#endif /* NO_BCACHEFS_FS */