Move the iomap_readpage_iter() bio read logic into a separate helper
function, iomap_bio_read_folio_range(). This is needed to make iomap
read/readahead more generically usable, especially for filesystems that
do not require CONFIG_BLOCK.

Additionally rename buffered write's iomap_read_folio_range() function
to iomap_bio_read_folio_range_sync() to better describe its synchronous
behavior.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 68 ++++++++++++++++++++++++------------------
 1 file changed, 39 insertions(+), 29 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index fd827398afd2..05399aaa1361 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -357,36 +357,15 @@ struct iomap_readpage_ctx {
 	struct readahead_control *rac;
 };
 
-static int iomap_readpage_iter(struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx)
+static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
+		struct iomap_readpage_ctx *ctx, loff_t pos, size_t plen)
 {
+	struct folio *folio = ctx->cur_folio;
 	const struct iomap *iomap = &iter->iomap;
-	loff_t pos = iter->pos;
+	struct iomap_folio_state *ifs = folio->private;
+	size_t poff = offset_in_folio(folio, pos);
 	loff_t length = iomap_length(iter);
-	struct folio *folio = ctx->cur_folio;
-	struct iomap_folio_state *ifs;
-	size_t poff, plen;
 	sector_t sector;
-	int ret;
-
-	if (iomap->type == IOMAP_INLINE) {
-		ret = iomap_read_inline_data(iter, folio);
-		if (ret)
-			return ret;
-		return iomap_iter_advance(iter, &length);
-	}
-
-	/* zero post-eof blocks as the page may be mapped */
-	ifs = ifs_alloc(iter->inode, folio, iter->flags);
-	iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff, &plen);
-	if (plen == 0)
-		goto done;
-
-	if (iomap_block_needs_zeroing(iter, pos)) {
-		folio_zero_range(folio, poff, plen);
-		iomap_set_range_uptodate(folio, poff, plen);
-		goto done;
-	}
 
 	ctx->cur_folio_in_bio = true;
 	if (ifs) {
@@ -425,6 +404,37 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 		ctx->bio->bi_end_io = iomap_read_end_io;
 		bio_add_folio_nofail(ctx->bio, folio, plen, poff);
 	}
+}
+
+static int iomap_readpage_iter(struct iomap_iter *iter,
+		struct iomap_readpage_ctx *ctx)
+{
+	const struct iomap *iomap = &iter->iomap;
+	loff_t pos = iter->pos;
+	loff_t length = iomap_length(iter);
+	struct folio *folio = ctx->cur_folio;
+	size_t poff, plen;
+	int ret;
+
+	if (iomap->type == IOMAP_INLINE) {
+		ret = iomap_read_inline_data(iter, folio);
+		if (ret)
+			return ret;
+		return iomap_iter_advance(iter, &length);
+	}
+
+	/* zero post-eof blocks as the page may be mapped */
+	ifs_alloc(iter->inode, folio, iter->flags);
+	iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff, &plen);
+	if (plen == 0)
+		goto done;
+
+	if (iomap_block_needs_zeroing(iter, pos)) {
+		folio_zero_range(folio, poff, plen);
+		iomap_set_range_uptodate(folio, poff, plen);
+	} else {
+		iomap_bio_read_folio_range(iter, ctx, pos, plen);
+	}
 
 done:
 	/*
@@ -549,7 +559,7 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
 
-static int iomap_read_folio_range(const struct iomap_iter *iter,
+static int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
 		struct folio *folio, loff_t pos, size_t len)
 {
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
@@ -562,7 +572,7 @@ static int iomap_read_folio_range(const struct iomap_iter *iter,
 	return submit_bio_wait(&bio);
 }
 #else
-static int iomap_read_folio_range(const struct iomap_iter *iter,
+static int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
 		struct folio *folio, loff_t pos, size_t len)
 {
 	WARN_ON_ONCE(1);
@@ -739,7 +749,7 @@ static int __iomap_write_begin(const struct iomap_iter *iter,
 				status = write_ops->read_folio_range(iter,
 						folio, block_start, plen);
 			else
-				status = iomap_read_folio_range(iter,
+				status = iomap_bio_read_folio_range_sync(iter,
 						folio, block_start, plen);
 			if (status)
 				return status;
-- 
2.47.3

Move the read/readahead bio submission logic into a separate helper.
This is needed to make iomap read/readahead more generically usable,
especially for filesystems that do not require CONFIG_BLOCK.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 05399aaa1361..ee96558b6d99 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -357,6 +357,14 @@ struct iomap_readpage_ctx {
 	struct readahead_control *rac;
 };
 
+static void iomap_bio_submit_read(struct iomap_readpage_ctx *ctx)
+{
+	struct bio *bio = ctx->bio;
+
+	if (bio)
+		submit_bio(bio);
+}
+
 static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 		struct iomap_readpage_ctx *ctx, loff_t pos, size_t plen)
 {
@@ -382,8 +390,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 		gfp_t orig_gfp = gfp;
 		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
 
-		if (ctx->bio)
-			submit_bio(ctx->bio);
+		iomap_bio_submit_read(ctx);
 
 		if (ctx->rac) /* same as readahead_gfp_mask */
 			gfp |= __GFP_NORETRY | __GFP_NOWARN;
@@ -478,13 +485,10 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	while ((ret = iomap_iter(&iter, ops)) > 0)
 		iter.status = iomap_read_folio_iter(&iter, &ctx);
 
-	if (ctx.bio) {
-		submit_bio(ctx.bio);
-		WARN_ON_ONCE(!ctx.cur_folio_in_bio);
-	} else {
-		WARN_ON_ONCE(ctx.cur_folio_in_bio);
+	iomap_bio_submit_read(&ctx);
+
+	if (!ctx.cur_folio_in_bio)
 		folio_unlock(folio);
-	}
 
 	/*
 	 * Just like mpage_readahead and block_read_full_folio, we always
@@ -550,12 +554,10 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 	while (iomap_iter(&iter, ops) > 0)
 		iter.status = iomap_readahead_iter(&iter, &ctx);
 
-	if (ctx.bio)
-		submit_bio(ctx.bio);
-	if (ctx.cur_folio) {
-		if (!ctx.cur_folio_in_bio)
-			folio_unlock(ctx.cur_folio);
-	}
+	iomap_bio_submit_read(&ctx);
+
+	if (ctx.cur_folio && !ctx.cur_folio_in_bio)
+		folio_unlock(ctx.cur_folio);
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
 
-- 
2.47.3

Store the iomap_readpage_ctx bio generically as a "void *read_ctx".
This makes the read/readahead interface more generic, which allows it to
be used by filesystems that may not be block-based and may not have
CONFIG_BLOCK set.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index ee96558b6d99..2a1709e0757b 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -353,13 +353,13 @@ static void iomap_read_end_io(struct bio *bio)
 struct iomap_readpage_ctx {
 	struct folio		*cur_folio;
 	bool			cur_folio_in_bio;
-	struct bio		*bio;
+	void			*read_ctx;
 	struct readahead_control *rac;
 };
 
 static void iomap_bio_submit_read(struct iomap_readpage_ctx *ctx)
 {
-	struct bio *bio = ctx->bio;
+	struct bio *bio = ctx->read_ctx;
 
 	if (bio)
 		submit_bio(bio);
@@ -374,6 +374,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 	size_t poff = offset_in_folio(folio, pos);
 	loff_t length = iomap_length(iter);
 	sector_t sector;
+	struct bio *bio = ctx->read_ctx;
 
 	ctx->cur_folio_in_bio = true;
 	if (ifs) {
@@ -383,9 +384,8 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 	}
 
 	sector = iomap_sector(iomap, pos);
-	if (!ctx->bio ||
-	    bio_end_sector(ctx->bio) != sector ||
-	    !bio_add_folio(ctx->bio, folio, plen, poff)) {
+	if (!bio || bio_end_sector(bio) != sector ||
+	    !bio_add_folio(bio, folio, plen, poff)) {
 		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
 		gfp_t orig_gfp = gfp;
 		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
@@ -394,22 +394,21 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 
 		if (ctx->rac) /* same as readahead_gfp_mask */
 			gfp |= __GFP_NORETRY | __GFP_NOWARN;
-		ctx->bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs),
-				     REQ_OP_READ, gfp);
+		bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ,
+				     gfp);
 		/*
 		 * If the bio_alloc fails, try it again for a single page to
 		 * avoid having to deal with partial page reads.  This emulates
 		 * what do_mpage_read_folio does.
 		 */
-		if (!ctx->bio) {
-			ctx->bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ,
-					     orig_gfp);
-		}
+		if (!bio)
+			bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
 		if (ctx->rac)
-			ctx->bio->bi_opf |= REQ_RAHEAD;
-		ctx->bio->bi_iter.bi_sector = sector;
-		ctx->bio->bi_end_io = iomap_read_end_io;
-		bio_add_folio_nofail(ctx->bio, folio, plen, poff);
+			bio->bi_opf |= REQ_RAHEAD;
+		bio->bi_iter.bi_sector = sector;
+		bio->bi_end_io = iomap_read_end_io;
+		bio_add_folio_nofail(bio, folio, plen, poff);
+		ctx->read_ctx = bio;
 	}
 }
 
-- 
2.47.3

Iterate over all non-uptodate ranges in a single call to
iomap_readpage_iter() instead of leaving the partial folio iteration to
the caller.

This will be useful for supporting caller-provided async folio read
callbacks (added in later commit) because that will require tracking
when the first and last async read request for a folio is sent, in order
to prevent premature read completion of the folio.

This additionally makes the iomap_readahead_iter() logic a bit simpler.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/buffered-io.c | 69 ++++++++++++++++++++----------------------
 1 file changed, 32 insertions(+), 37 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 2a1709e0757b..0c4ba2a63490 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -420,6 +420,7 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 	loff_t length = iomap_length(iter);
 	struct folio *folio = ctx->cur_folio;
 	size_t poff, plen;
+	loff_t count;
 	int ret;
 
 	if (iomap->type == IOMAP_INLINE) {
@@ -431,39 +432,33 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 
 	/* zero post-eof blocks as the page may be mapped */
 	ifs_alloc(iter->inode, folio, iter->flags);
-	iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff, &plen);
-	if (plen == 0)
-		goto done;
 
-	if (iomap_block_needs_zeroing(iter, pos)) {
-		folio_zero_range(folio, poff, plen);
-		iomap_set_range_uptodate(folio, poff, plen);
-	} else {
-		iomap_bio_read_folio_range(iter, ctx, pos, plen);
-	}
+	length = min_t(loff_t, length,
+			folio_size(folio) - offset_in_folio(folio, pos));
+	while (length) {
+		iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff,
+				&plen);
 
-done:
-	/*
-	 * Move the caller beyond our range so that it keeps making progress.
-	 * For that, we have to include any leading non-uptodate ranges, but
-	 * we can skip trailing ones as they will be handled in the next
-	 * iteration.
-	 */
-	length = pos - iter->pos + plen;
-	return iomap_iter_advance(iter, &length);
-}
+		count = pos - iter->pos + plen;
+		if (WARN_ON_ONCE(count > length))
+			return -EIO;
 
-static int iomap_read_folio_iter(struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx)
-{
-	int ret;
+		if (plen == 0)
+			return iomap_iter_advance(iter, &count);
 
-	while (iomap_length(iter)) {
-		ret = iomap_readpage_iter(iter, ctx);
+		if (iomap_block_needs_zeroing(iter, pos)) {
+			folio_zero_range(folio, poff, plen);
+			iomap_set_range_uptodate(folio, poff, plen);
+		} else {
+			iomap_bio_read_folio_range(iter, ctx, pos, plen);
+		}
+
+		length -= count;
+		ret = iomap_iter_advance(iter, &count);
 		if (ret)
 			return ret;
+		pos = iter->pos;
 	}
-
 	return 0;
 }
 
@@ -482,7 +477,7 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
-		iter.status = iomap_read_folio_iter(&iter, &ctx);
+		iter.status = iomap_readpage_iter(&iter, &ctx);
 
 	iomap_bio_submit_read(&ctx);
 
@@ -504,16 +499,16 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 	int ret;
 
 	while (iomap_length(iter)) {
-		if (ctx->cur_folio &&
-		    offset_in_folio(ctx->cur_folio, iter->pos) == 0) {
-			if (!ctx->cur_folio_in_bio)
-				folio_unlock(ctx->cur_folio);
-			ctx->cur_folio = NULL;
-		}
-		if (!ctx->cur_folio) {
-			ctx->cur_folio = readahead_folio(ctx->rac);
-			ctx->cur_folio_in_bio = false;
-		}
+		if (ctx->cur_folio && !ctx->cur_folio_in_bio)
+			folio_unlock(ctx->cur_folio);
+		ctx->cur_folio = readahead_folio(ctx->rac);
+		/*
+		 * We should never in practice hit this case since the iter
+		 * length matches the readahead length.
+		 */
+		if (WARN_ON_ONCE(!ctx->cur_folio))
+			return -EINVAL;
+		ctx->cur_folio_in_bio = false;
 		ret = iomap_readpage_iter(iter, ctx);
 		if (ret)
 			return ret;
-- 
2.47.3

->readpage was deprecated and reads are now on folios.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/buffered-io.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 0c4ba2a63490..d6266cb702e3 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -412,7 +412,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 	}
 }
 
-static int iomap_readpage_iter(struct iomap_iter *iter,
+static int iomap_read_folio_iter(struct iomap_iter *iter,
 		struct iomap_readpage_ctx *ctx)
 {
 	const struct iomap *iomap = &iter->iomap;
@@ -477,7 +477,7 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
-		iter.status = iomap_readpage_iter(&iter, &ctx);
+		iter.status = iomap_read_folio_iter(&iter, &ctx);
 
 	iomap_bio_submit_read(&ctx);
 
@@ -509,7 +509,7 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 		if (WARN_ON_ONCE(!ctx->cur_folio))
 			return -EINVAL;
 		ctx->cur_folio_in_bio = false;
-		ret = iomap_readpage_iter(iter, ctx);
+		ret = iomap_read_folio_iter(iter, ctx);
 		if (ret)
 			return ret;
 	}
-- 
2.47.3

->readpage was deprecated and reads are now on folios.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/buffered-io.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index d6266cb702e3..6c5a631848b7 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -350,14 +350,14 @@ static void iomap_read_end_io(struct bio *bio)
 	bio_put(bio);
 }
 
-struct iomap_readpage_ctx {
+struct iomap_read_folio_ctx {
 	struct folio		*cur_folio;
 	bool			cur_folio_in_bio;
 	void			*read_ctx;
 	struct readahead_control *rac;
 };
 
-static void iomap_bio_submit_read(struct iomap_readpage_ctx *ctx)
+static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
 {
 	struct bio *bio = ctx->read_ctx;
 
@@ -366,7 +366,7 @@ static void iomap_bio_submit_read(struct iomap_readpage_ctx *ctx)
 }
 
 static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx, loff_t pos, size_t plen)
+		struct iomap_read_folio_ctx *ctx, loff_t pos, size_t plen)
 {
 	struct folio *folio = ctx->cur_folio;
 	const struct iomap *iomap = &iter->iomap;
@@ -413,7 +413,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 }
 
 static int iomap_read_folio_iter(struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx)
+		struct iomap_read_folio_ctx *ctx)
 {
 	const struct iomap *iomap = &iter->iomap;
 	loff_t pos = iter->pos;
@@ -469,7 +469,7 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 		.pos		= folio_pos(folio),
 		.len		= folio_size(folio),
 	};
-	struct iomap_readpage_ctx ctx = {
+	struct iomap_read_folio_ctx ctx = {
 		.cur_folio	= folio,
 	};
 	int ret;
@@ -494,7 +494,7 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 EXPORT_SYMBOL_GPL(iomap_read_folio);
 
 static int iomap_readahead_iter(struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx)
+		struct iomap_read_folio_ctx *ctx)
 {
 	int ret;
 
@@ -539,7 +539,7 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 		.pos	= readahead_pos(rac),
 		.len	= readahead_length(rac),
 	};
-	struct iomap_readpage_ctx ctx = {
+	struct iomap_read_folio_ctx ctx = {
 		.rac	= rac,
 	};
 
-- 
2.47.3

The purpose of "struct iomap_read_folio_ctx->cur_folio_in_bio" is to
track folio ownership to know who is responsible for unlocking it.
Rename "cur_folio_in_bio" to "cur_folio_owned" to better reflect this
purpose and so that this can be generically used later on by filesystems
that are not block-based.

Since "struct iomap_read_folio_ctx" will be made a public interface
later on when read/readahead takes in caller-provided callbacks, track
the folio ownership state internally instead of exposing it in "struct
iomap_read_folio_ctx" to make the interface simpler for end users.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 6c5a631848b7..587bbdbd24bc 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -352,7 +352,6 @@ static void iomap_read_end_io(struct bio *bio)
 
 struct iomap_read_folio_ctx {
 	struct folio		*cur_folio;
-	bool			cur_folio_in_bio;
 	void			*read_ctx;
 	struct readahead_control *rac;
 };
@@ -376,7 +375,6 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 	sector_t sector;
 	struct bio *bio = ctx->read_ctx;
 
-	ctx->cur_folio_in_bio = true;
 	if (ifs) {
 		spin_lock_irq(&ifs->state_lock);
 		ifs->read_bytes_pending += plen;
@@ -413,7 +411,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 }
 
 static int iomap_read_folio_iter(struct iomap_iter *iter,
-		struct iomap_read_folio_ctx *ctx)
+		struct iomap_read_folio_ctx *ctx, bool *cur_folio_owned)
 {
 	const struct iomap *iomap = &iter->iomap;
 	loff_t pos = iter->pos;
@@ -450,6 +448,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 			folio_zero_range(folio, poff, plen);
 			iomap_set_range_uptodate(folio, poff, plen);
 		} else {
+			*cur_folio_owned = true;
 			iomap_bio_read_folio_range(iter, ctx, pos, plen);
 		}
 
@@ -472,16 +471,22 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	struct iomap_read_folio_ctx ctx = {
 		.cur_folio	= folio,
 	};
+	/*
+	 * If an external IO helper takes ownership of the folio, it is
+	 * responsible for unlocking it when the read completes.
+	 */
+	bool cur_folio_owned = false;
 	int ret;
 
 	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
-		iter.status = iomap_read_folio_iter(&iter, &ctx);
+		iter.status = iomap_read_folio_iter(&iter, &ctx,
+				&cur_folio_owned);
 
 	iomap_bio_submit_read(&ctx);
 
-	if (!ctx.cur_folio_in_bio)
+	if (!cur_folio_owned)
 		folio_unlock(folio);
 
 	/*
@@ -494,12 +499,13 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 EXPORT_SYMBOL_GPL(iomap_read_folio);
 
 static int iomap_readahead_iter(struct iomap_iter *iter,
-		struct iomap_read_folio_ctx *ctx)
+		struct iomap_read_folio_ctx *ctx,
+		bool *cur_folio_owned)
 {
 	int ret;
 
 	while (iomap_length(iter)) {
-		if (ctx->cur_folio && !ctx->cur_folio_in_bio)
+		if (ctx->cur_folio && !*cur_folio_owned)
 			folio_unlock(ctx->cur_folio);
 		ctx->cur_folio = readahead_folio(ctx->rac);
 		/*
@@ -508,8 +514,8 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 		 */
 		if (WARN_ON_ONCE(!ctx->cur_folio))
 			return -EINVAL;
-		ctx->cur_folio_in_bio = false;
-		ret = iomap_read_folio_iter(iter, ctx);
+		*cur_folio_owned = false;
+		ret = iomap_read_folio_iter(iter, ctx, cur_folio_owned);
 		if (ret)
 			return ret;
 	}
@@ -542,15 +548,21 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 	struct iomap_read_folio_ctx ctx = {
 		.rac	= rac,
 	};
+	/*
+	 * If an external IO helper takes ownership of the folio, it is
+	 * responsible for unlocking it when the read completes.
+	 */
+	bool cur_folio_owned = false;
 
 	trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
 
 	while (iomap_iter(&iter, ops) > 0)
-		iter.status = iomap_readahead_iter(&iter, &ctx);
+		iter.status = iomap_readahead_iter(&iter, &ctx,
+					&cur_folio_owned);
 
 	iomap_bio_submit_read(&ctx);
 
-	if (ctx.cur_folio && !ctx.cur_folio_in_bio)
+	if (ctx.cur_folio && !cur_folio_owned)
 		folio_unlock(ctx.cur_folio);
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
-- 
2.47.3

Move ifs read_bytes_pending increment logic into a separate helper,
iomap_start_folio_read(), which will be needed later on by
caller-provided read callbacks (added in a later commit) for
read/readahead. This is the counterpart to the currently existing
iomap_finish_folio_read().

Make iomap_start_folio_read() and iomap_finish_folio_read() publicly
accessible. These need to be accessible in order for caller-provided
read callbacks to use.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/buffered-io.c | 26 +++++++++++++++++---------
 include/linux/iomap.h  |  3 +++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 587bbdbd24bc..379438970347 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -317,9 +317,20 @@ static int iomap_read_inline_data(const struct iomap_iter *iter,
 	return 0;
 }
 
-#ifdef CONFIG_BLOCK
-static void iomap_finish_folio_read(struct folio *folio, size_t off,
-		size_t len, int error)
+void iomap_start_folio_read(struct folio *folio, size_t len)
+{
+	struct iomap_folio_state *ifs = folio->private;
+
+	if (ifs) {
+		spin_lock_irq(&ifs->state_lock);
+		ifs->read_bytes_pending += len;
+		spin_unlock_irq(&ifs->state_lock);
+	}
+}
+EXPORT_SYMBOL_GPL(iomap_start_folio_read);
+
+void iomap_finish_folio_read(struct folio *folio, size_t off, size_t len,
+		int error)
 {
 	struct iomap_folio_state *ifs = folio->private;
 	bool uptodate = !error;
@@ -339,7 +350,9 @@ static void iomap_finish_folio_read(struct folio *folio, size_t off,
 	if (finished)
 		folio_end_read(folio, uptodate);
 }
+EXPORT_SYMBOL_GPL(iomap_finish_folio_read);
 
+#ifdef CONFIG_BLOCK
 static void iomap_read_end_io(struct bio *bio)
 {
 	int error = blk_status_to_errno(bio->bi_status);
@@ -369,17 +382,12 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 {
 	struct folio *folio = ctx->cur_folio;
 	const struct iomap *iomap = &iter->iomap;
-	struct iomap_folio_state *ifs = folio->private;
 	size_t poff = offset_in_folio(folio, pos);
 	loff_t length = iomap_length(iter);
 	sector_t sector;
 	struct bio *bio = ctx->read_ctx;
 
-	if (ifs) {
-		spin_lock_irq(&ifs->state_lock);
-		ifs->read_bytes_pending += plen;
-		spin_unlock_irq(&ifs->state_lock);
-	}
+	iomap_start_folio_read(folio, plen);
 
 	sector = iomap_sector(iomap, pos);
 	if (!bio || bio_end_sector(bio) != sector ||
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 73dceabc21c8..0938c4a57f4c 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -467,6 +467,9 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 		loff_t pos, loff_t end_pos, unsigned int dirty_len);
 int iomap_ioend_writeback_submit(struct iomap_writepage_ctx *wpc, int error);
 
+void iomap_start_folio_read(struct folio *folio, size_t len);
+void iomap_finish_folio_read(struct folio *folio, size_t off, size_t len,
+		int error);
 void iomap_start_folio_write(struct inode *inode, struct folio *folio,
 		size_t len);
 void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
-- 
2.47.3

Add caller-provided callbacks for read and readahead so that it can be
used generically, especially by filesystems that are not block-based.

In particular, this:
* Modifies the read and readahead interface to take in a
  struct iomap_read_folio_ctx that is publicly defined as:

  struct iomap_read_folio_ctx {
	const struct iomap_read_ops *ops;
	struct folio *cur_folio;
	struct readahead_control *rac;
	void *read_ctx;
  };

  where struct iomap_read_ops is defined as:

  struct iomap_read_ops {
      int (*read_folio_range)(const struct iomap_iter *iter,
                             struct iomap_read_folio_ctx *ctx,
                             size_t len);
      void (*read_submit)(struct iomap_read_folio_ctx *ctx);
  };

  read_folio_range() reads in the folio range and is required by the
  caller to provide. read_submit() is optional and is used for
  submitting any pending read requests.

* Modifies existing filesystems that use iomap for read and readahead to
  use the new API, through the new statically inlined helpers
  iomap_bio_read_folio() and iomap_bio_readahead(). There is no change
  in functinality for those filesystems.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 .../filesystems/iomap/operations.rst          | 45 ++++++++++++
 block/fops.c                                  |  5 +-
 fs/erofs/data.c                               |  5 +-
 fs/gfs2/aops.c                                |  6 +-
 fs/iomap/buffered-io.c                        | 69 +++++++++++--------
 fs/xfs/xfs_aops.c                             |  5 +-
 fs/zonefs/file.c                              |  5 +-
 include/linux/iomap.h                         | 62 ++++++++++++++++-
 8 files changed, 159 insertions(+), 43 deletions(-)

diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst
index 067ed8e14ef3..dbb193415c0e 100644
--- a/Documentation/filesystems/iomap/operations.rst
+++ b/Documentation/filesystems/iomap/operations.rst
@@ -135,6 +135,29 @@ These ``struct kiocb`` flags are significant for buffered I/O with iomap:
 
  * ``IOCB_DONTCACHE``: Turns on ``IOMAP_DONTCACHE``.
 
+``struct iomap_read_ops``
+--------------------------
+
+.. code-block:: c
+
+ struct iomap_read_ops {
+     int (*read_folio_range)(const struct iomap_iter *iter,
+                             struct iomap_read_folio_ctx *ctx, size_t len);
+     void (*submit_read)(struct iomap_read_folio_ctx *ctx);
+ };
+
+iomap calls these functions:
+
+  - ``read_folio_range``: Called to read in the range. This must be provided
+    by the caller. The caller is responsible for calling
+    iomap_start_folio_read() and iomap_finish_folio_read() before and after
+    reading in the folio range. This should be done even if an error is
+    encountered during the read. This returns 0 on success or a negative error
+    on failure.
+
+  - ``submit_read``: Submit any pending read requests. This function is
+    optional.
+
 Internal per-Folio State
 ------------------------
 
@@ -182,6 +205,28 @@ The ``flags`` argument to ``->iomap_begin`` will be set to zero.
 The pagecache takes whatever locks it needs before calling the
 filesystem.
 
+Both ``iomap_readahead`` and ``iomap_read_folio`` pass in a ``struct
+iomap_read_folio_ctx``:
+
+.. code-block:: c
+
+ struct iomap_read_folio_ctx {
+    const struct iomap_read_ops *ops;
+    struct folio *cur_folio;
+    struct readahead_control *rac;
+    void *read_ctx;
+ };
+
+``iomap_readahead`` must set:
+ * ``ops->read_folio_range()`` and ``rac``
+
+``iomap_read_folio`` must set:
+ * ``ops->read_folio_range()`` and ``cur_folio``
+
+``ops->submit_read()`` and ``read_ctx`` are optional. ``read_ctx`` is used to
+pass in any custom data the caller needs accessible in the ops callbacks for
+fulfilling reads.
+
 Buffered Writes
 ---------------
 
diff --git a/block/fops.c b/block/fops.c
index ddbc69c0922b..a2c2391d8dfa 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -533,12 +533,13 @@ const struct address_space_operations def_blk_aops = {
 #else /* CONFIG_BUFFER_HEAD */
 static int blkdev_read_folio(struct file *file, struct folio *folio)
 {
-	return iomap_read_folio(folio, &blkdev_iomap_ops);
+	iomap_bio_read_folio(folio, &blkdev_iomap_ops);
+	return 0;
 }
 
 static void blkdev_readahead(struct readahead_control *rac)
 {
-	iomap_readahead(rac, &blkdev_iomap_ops);
+	iomap_bio_readahead(rac, &blkdev_iomap_ops);
 }
 
 static ssize_t blkdev_writeback_range(struct iomap_writepage_ctx *wpc,
diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 3b1ba571c728..be4191b33321 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -371,7 +371,8 @@ static int erofs_read_folio(struct file *file, struct folio *folio)
 {
 	trace_erofs_read_folio(folio, true);
 
-	return iomap_read_folio(folio, &erofs_iomap_ops);
+	iomap_bio_read_folio(folio, &erofs_iomap_ops);
+	return 0;
 }
 
 static void erofs_readahead(struct readahead_control *rac)
@@ -379,7 +380,7 @@ static void erofs_readahead(struct readahead_control *rac)
 	trace_erofs_readahead(rac->mapping->host, readahead_index(rac),
 					readahead_count(rac), true);
 
-	return iomap_readahead(rac, &erofs_iomap_ops);
+	iomap_bio_readahead(rac, &erofs_iomap_ops);
 }
 
 static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 47d74afd63ac..38d4f343187a 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -424,11 +424,11 @@ static int gfs2_read_folio(struct file *file, struct folio *folio)
 	struct inode *inode = folio->mapping->host;
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
-	int error;
+	int error = 0;
 
 	if (!gfs2_is_jdata(ip) ||
 	    (i_blocksize(inode) == PAGE_SIZE && !folio_buffers(folio))) {
-		error = iomap_read_folio(folio, &gfs2_iomap_ops);
+		iomap_bio_read_folio(folio, &gfs2_iomap_ops);
 	} else if (gfs2_is_stuffed(ip)) {
 		error = stuffed_read_folio(ip, folio);
 	} else {
@@ -503,7 +503,7 @@ static void gfs2_readahead(struct readahead_control *rac)
 	else if (gfs2_is_jdata(ip))
 		mpage_readahead(rac, gfs2_block_map);
 	else
-		iomap_readahead(rac, &gfs2_iomap_ops);
+		iomap_bio_readahead(rac, &gfs2_iomap_ops);
 }
 
 /**
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 379438970347..561378f2b9bb 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -363,12 +363,6 @@ static void iomap_read_end_io(struct bio *bio)
 	bio_put(bio);
 }
 
-struct iomap_read_folio_ctx {
-	struct folio		*cur_folio;
-	void			*read_ctx;
-	struct readahead_control *rac;
-};
-
 static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
 {
 	struct bio *bio = ctx->read_ctx;
@@ -377,11 +371,12 @@ static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
 		submit_bio(bio);
 }
 
-static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
-		struct iomap_read_folio_ctx *ctx, loff_t pos, size_t plen)
+static int iomap_bio_read_folio_range(const struct iomap_iter *iter,
+		struct iomap_read_folio_ctx *ctx, size_t plen)
 {
 	struct folio *folio = ctx->cur_folio;
 	const struct iomap *iomap = &iter->iomap;
+	loff_t pos = iter->pos;
 	size_t poff = offset_in_folio(folio, pos);
 	loff_t length = iomap_length(iter);
 	sector_t sector;
@@ -416,8 +411,15 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
 		bio_add_folio_nofail(bio, folio, plen, poff);
 		ctx->read_ctx = bio;
 	}
+	return 0;
 }
 
+const struct iomap_read_ops iomap_bio_read_ops = {
+	.read_folio_range	= iomap_bio_read_folio_range,
+	.submit_read		= iomap_bio_submit_read,
+};
+EXPORT_SYMBOL_GPL(iomap_bio_read_ops);
+
 static int iomap_read_folio_iter(struct iomap_iter *iter,
 		struct iomap_read_folio_ctx *ctx, bool *cur_folio_owned)
 {
@@ -426,7 +428,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 	loff_t length = iomap_length(iter);
 	struct folio *folio = ctx->cur_folio;
 	size_t poff, plen;
-	loff_t count;
+	loff_t delta;
 	int ret;
 
 	if (iomap->type == IOMAP_INLINE) {
@@ -445,23 +447,30 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 		iomap_adjust_read_range(iter->inode, folio, &pos, length, &poff,
 				&plen);
 
-		count = pos - iter->pos + plen;
-		if (WARN_ON_ONCE(count > length))
+		delta = pos - iter->pos;
+		if (WARN_ON_ONCE(delta + plen > length))
 			return -EIO;
+		length -= delta + plen;
+
+		ret = iomap_iter_advance(iter, &delta);
+		if (ret)
+			return ret;
 
 		if (plen == 0)
-			return iomap_iter_advance(iter, &count);
+			return 0;
 
 		if (iomap_block_needs_zeroing(iter, pos)) {
 			folio_zero_range(folio, poff, plen);
 			iomap_set_range_uptodate(folio, poff, plen);
 		} else {
 			*cur_folio_owned = true;
-			iomap_bio_read_folio_range(iter, ctx, pos, plen);
+			ret = ctx->ops->read_folio_range(iter, ctx, plen);
+			if (ret)
+				return ret;
 		}
 
-		length -= count;
-		ret = iomap_iter_advance(iter, &count);
+		delta = plen;
+		ret = iomap_iter_advance(iter, &delta);
 		if (ret)
 			return ret;
 		pos = iter->pos;
@@ -469,16 +478,15 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 	return 0;
 }
 
-int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
+int iomap_read_folio(const struct iomap_ops *ops,
+		struct iomap_read_folio_ctx *ctx)
 {
+	struct folio *folio = ctx->cur_folio;
 	struct iomap_iter iter = {
 		.inode		= folio->mapping->host,
 		.pos		= folio_pos(folio),
 		.len		= folio_size(folio),
 	};
-	struct iomap_read_folio_ctx ctx = {
-		.cur_folio	= folio,
-	};
 	/*
 	 * If an external IO helper takes ownership of the folio, it is
 	 * responsible for unlocking it when the read completes.
@@ -489,10 +497,11 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
-		iter.status = iomap_read_folio_iter(&iter, &ctx,
+		iter.status = iomap_read_folio_iter(&iter, ctx,
 				&cur_folio_owned);
 
-	iomap_bio_submit_read(&ctx);
+	if (ctx->ops->submit_read)
+		ctx->ops->submit_read(ctx);
 
 	if (!cur_folio_owned)
 		folio_unlock(folio);
@@ -533,8 +542,8 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 
 /**
  * iomap_readahead - Attempt to read pages from a file.
- * @rac: Describes the pages to be read.
  * @ops: The operations vector for the filesystem.
+ * @ctx: The ctx used for issuing readahead.
  *
  * This function is for filesystems to call to implement their readahead
  * address_space operation.
@@ -546,16 +555,15 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
  * function is called with memalloc_nofs set, so allocations will not cause
  * the filesystem to be reentered.
  */
-void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
+void iomap_readahead(const struct iomap_ops *ops,
+		struct iomap_read_folio_ctx *ctx)
 {
+	struct readahead_control *rac = ctx->rac;
 	struct iomap_iter iter = {
 		.inode	= rac->mapping->host,
 		.pos	= readahead_pos(rac),
 		.len	= readahead_length(rac),
 	};
-	struct iomap_read_folio_ctx ctx = {
-		.rac	= rac,
-	};
 	/*
 	 * If an external IO helper takes ownership of the folio, it is
 	 * responsible for unlocking it when the read completes.
@@ -565,13 +573,14 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 	trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
 
 	while (iomap_iter(&iter, ops) > 0)
-		iter.status = iomap_readahead_iter(&iter, &ctx,
+		iter.status = iomap_readahead_iter(&iter, ctx,
 					&cur_folio_owned);
 
-	iomap_bio_submit_read(&ctx);
+	if (ctx->ops->submit_read)
+		ctx->ops->submit_read(ctx);
 
-	if (ctx.cur_folio && !cur_folio_owned)
-		folio_unlock(ctx.cur_folio);
+	if (ctx->cur_folio && !cur_folio_owned)
+		folio_unlock(ctx->cur_folio);
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
 
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index a26f79815533..0c2ed00733f2 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -742,14 +742,15 @@ xfs_vm_read_folio(
 	struct file		*unused,
 	struct folio		*folio)
 {
-	return iomap_read_folio(folio, &xfs_read_iomap_ops);
+	iomap_bio_read_folio(folio, &xfs_read_iomap_ops);
+	return 0;
 }
 
 STATIC void
 xfs_vm_readahead(
 	struct readahead_control	*rac)
 {
-	iomap_readahead(rac, &xfs_read_iomap_ops);
+	iomap_bio_readahead(rac, &xfs_read_iomap_ops);
 }
 
 static int
diff --git a/fs/zonefs/file.c b/fs/zonefs/file.c
index fd3a5922f6c3..4d6e7eb52966 100644
--- a/fs/zonefs/file.c
+++ b/fs/zonefs/file.c
@@ -112,12 +112,13 @@ static const struct iomap_ops zonefs_write_iomap_ops = {
 
 static int zonefs_read_folio(struct file *unused, struct folio *folio)
 {
-	return iomap_read_folio(folio, &zonefs_read_iomap_ops);
+	iomap_bio_read_folio(folio, &zonefs_read_iomap_ops);
+	return 0;
 }
 
 static void zonefs_readahead(struct readahead_control *rac)
 {
-	iomap_readahead(rac, &zonefs_read_iomap_ops);
+	iomap_bio_readahead(rac, &zonefs_read_iomap_ops);
 }
 
 /*
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 0938c4a57f4c..4a168ebb40f5 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -16,6 +16,7 @@ struct inode;
 struct iomap_iter;
 struct iomap_dio;
 struct iomap_writepage_ctx;
+struct iomap_read_folio_ctx;
 struct iov_iter;
 struct kiocb;
 struct page;
@@ -339,8 +340,10 @@ static inline bool iomap_want_unshare_iter(const struct iomap_iter *iter)
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops,
 		const struct iomap_write_ops *write_ops, void *private);
-int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops);
-void iomap_readahead(struct readahead_control *, const struct iomap_ops *ops);
+int iomap_read_folio(const struct iomap_ops *ops,
+		struct iomap_read_folio_ctx *ctx);
+void iomap_readahead(const struct iomap_ops *ops,
+		struct iomap_read_folio_ctx *ctx);
 bool iomap_is_partially_uptodate(struct folio *, size_t from, size_t count);
 struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len);
 bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags);
@@ -478,6 +481,35 @@ void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
 int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio);
 int iomap_writepages(struct iomap_writepage_ctx *wpc);
 
+struct iomap_read_folio_ctx {
+	const struct iomap_read_ops *ops;
+	struct folio		*cur_folio;
+	struct readahead_control *rac;
+	void			*read_ctx;
+};
+
+struct iomap_read_ops {
+	/*
+	 * Read in a folio range.
+	 *
+	 * The caller is responsible for calling iomap_start_folio_read() and
+	 * iomap_finish_folio_read() before and after reading in the folio
+	 * range. This should be done even if an error is encountered during the
+	 * read.
+	 *
+	 * Returns 0 on success or a negative error on failure.
+	 */
+	int (*read_folio_range)(const struct iomap_iter *iter,
+			struct iomap_read_folio_ctx *ctx, size_t len);
+
+	/*
+	 * Submit any pending read requests.
+	 *
+	 * This is optional.
+	 */
+	void (*submit_read)(struct iomap_read_folio_ctx *ctx);
+};
+
 /*
  * Flags for direct I/O ->end_io:
  */
@@ -543,4 +575,30 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
 
 extern struct bio_set iomap_ioend_bioset;
 
+#ifdef CONFIG_BLOCK
+extern const struct iomap_read_ops iomap_bio_read_ops;
+
+static inline void iomap_bio_read_folio(struct folio *folio,
+		const struct iomap_ops *ops)
+{
+	struct iomap_read_folio_ctx ctx = {
+		.ops		= &iomap_bio_read_ops,
+		.cur_folio	= folio,
+	};
+
+	iomap_read_folio(ops, &ctx);
+}
+
+static inline void iomap_bio_readahead(struct readahead_control *rac,
+		const struct iomap_ops *ops)
+{
+	struct iomap_read_folio_ctx ctx = {
+		.ops		= &iomap_bio_read_ops,
+		.rac		= rac,
+	};
+
+	iomap_readahead(ops, &ctx);
+}
+#endif /* CONFIG_BLOCK */
+
 #endif /* LINUX_IOMAP_H */
-- 
2.47.3

Non-block-based filesystems will be using iomap read/readahead. If they
handle reading in ranges asynchronously and fulfill those read requests
on an ongoing basis (instead of all together at the end), then there is
the possibility that the read on the folio may be prematurely ended if
earlier async requests complete before the later ones have been issued.

For example if there is a large folio and a readahead request for 16
pages in that folio, if doing readahead on those 16 pages is split into
4 async requests and the first request is sent off and then completed
before we have sent off the second request, then when the first request
calls iomap_finish_folio_read(), ifs->read_bytes_pending would be 0,
which would end the read and unlock the folio prematurely.

To mitigate this, a "bias" is added to ifs->read_bytes_pending before
the first range is forwarded to the caller and removed after the last
range has been forwarded.

iomap writeback does this with their async requests as well to prevent
prematurely ending writeback.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 55 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 561378f2b9bb..667a49cb5ae5 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -420,6 +420,38 @@ const struct iomap_read_ops iomap_bio_read_ops = {
 };
 EXPORT_SYMBOL_GPL(iomap_bio_read_ops);
 
+/*
+ * Add a bias to ifs->read_bytes_pending to prevent the read on the folio from
+ * being ended prematurely.
+ *
+ * Otherwise, if the ranges are read asynchronously and read requests are
+ * fulfilled on an ongoing basis, there is the possibility that the read on the
+ * folio may be prematurely ended if earlier async requests complete before the
+ * later ones have been issued.
+ */
+static void iomap_read_add_bias(struct folio *folio)
+{
+	iomap_start_folio_read(folio, 1);
+}
+
+static void iomap_read_remove_bias(struct folio *folio, bool *cur_folio_owned)
+{
+	struct iomap_folio_state *ifs = folio->private;
+	bool finished, uptodate;
+
+	if (ifs) {
+		spin_lock_irq(&ifs->state_lock);
+		ifs->read_bytes_pending -= 1;
+		finished = !ifs->read_bytes_pending;
+		if (finished)
+			uptodate = ifs_is_fully_uptodate(folio, ifs);
+		spin_unlock_irq(&ifs->state_lock);
+		if (finished)
+			folio_end_read(folio, uptodate);
+		*cur_folio_owned = true;
+	}
+}
+
 static int iomap_read_folio_iter(struct iomap_iter *iter,
 		struct iomap_read_folio_ctx *ctx, bool *cur_folio_owned)
 {
@@ -429,7 +461,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 	struct folio *folio = ctx->cur_folio;
 	size_t poff, plen;
 	loff_t delta;
-	int ret;
+	int ret = 0;
 
 	if (iomap->type == IOMAP_INLINE) {
 		ret = iomap_read_inline_data(iter, folio);
@@ -441,6 +473,8 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 	/* zero post-eof blocks as the page may be mapped */
 	ifs_alloc(iter->inode, folio, iter->flags);
 
+	iomap_read_add_bias(folio);
+
 	length = min_t(loff_t, length,
 			folio_size(folio) - offset_in_folio(folio, pos));
 	while (length) {
@@ -448,16 +482,18 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 				&plen);
 
 		delta = pos - iter->pos;
-		if (WARN_ON_ONCE(delta + plen > length))
-			return -EIO;
+		if (WARN_ON_ONCE(delta + plen > length)) {
+			ret = -EIO;
+			break;
+		}
 		length -= delta + plen;
 
 		ret = iomap_iter_advance(iter, &delta);
 		if (ret)
-			return ret;
+			break;
 
 		if (plen == 0)
-			return 0;
+			break;
 
 		if (iomap_block_needs_zeroing(iter, pos)) {
 			folio_zero_range(folio, poff, plen);
@@ -466,16 +502,19 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 			*cur_folio_owned = true;
 			ret = ctx->ops->read_folio_range(iter, ctx, plen);
 			if (ret)
-				return ret;
+				break;
 		}
 
 		delta = plen;
 		ret = iomap_iter_advance(iter, &delta);
 		if (ret)
-			return ret;
+			break;
 		pos = iter->pos;
 	}
-	return 0;
+
+	iomap_read_remove_bias(folio, cur_folio_owned);
+
+	return ret;
 }
 
 int iomap_read_folio(const struct iomap_ops *ops,
-- 
2.47.3

Move bio logic in the buffered io code into its own file and remove
CONFIG_BLOCK gating for iomap read/readahead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/Makefile      |  3 +-
 fs/iomap/bio.c         | 90 ++++++++++++++++++++++++++++++++++++++++++
 fs/iomap/buffered-io.c | 90 +-----------------------------------------
 fs/iomap/internal.h    | 12 ++++++
 4 files changed, 105 insertions(+), 90 deletions(-)
 create mode 100644 fs/iomap/bio.c

diff --git a/fs/iomap/Makefile b/fs/iomap/Makefile
index f7e1c8534c46..a572b8808524 100644
--- a/fs/iomap/Makefile
+++ b/fs/iomap/Makefile
@@ -14,5 +14,6 @@ iomap-y				+= trace.o \
 iomap-$(CONFIG_BLOCK)		+= direct-io.o \
 				   ioend.o \
 				   fiemap.o \
-				   seek.o
+				   seek.o \
+				   bio.o
 iomap-$(CONFIG_SWAP)		+= swapfile.o
diff --git a/fs/iomap/bio.c b/fs/iomap/bio.c
new file mode 100644
index 000000000000..8a51c9d70268
--- /dev/null
+++ b/fs/iomap/bio.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2010 Red Hat, Inc.
+ * Copyright (C) 2016-2023 Christoph Hellwig.
+ */
+#include <linux/iomap.h>
+#include <linux/pagemap.h>
+#include "internal.h"
+#include "trace.h"
+
+static void iomap_read_end_io(struct bio *bio)
+{
+	int error = blk_status_to_errno(bio->bi_status);
+	struct folio_iter fi;
+
+	bio_for_each_folio_all(fi, bio)
+		iomap_finish_folio_read(fi.folio, fi.offset, fi.length, error);
+	bio_put(bio);
+}
+
+static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
+{
+	struct bio *bio = ctx->read_ctx;
+
+	if (bio)
+		submit_bio(bio);
+}
+
+static int iomap_bio_read_folio_range(const struct iomap_iter *iter,
+		struct iomap_read_folio_ctx *ctx, size_t plen)
+{
+	struct folio *folio = ctx->cur_folio;
+	const struct iomap *iomap = &iter->iomap;
+	loff_t pos = iter->pos;
+	size_t poff = offset_in_folio(folio, pos);
+	loff_t length = iomap_length(iter);
+	sector_t sector;
+	struct bio *bio = ctx->read_ctx;
+
+	iomap_start_folio_read(folio, plen);
+
+	sector = iomap_sector(iomap, pos);
+	if (!bio || bio_end_sector(bio) != sector ||
+	    !bio_add_folio(bio, folio, plen, poff)) {
+		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
+		gfp_t orig_gfp = gfp;
+		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
+
+		if (bio)
+			submit_bio(bio);
+
+		if (ctx->rac) /* same as readahead_gfp_mask */
+			gfp |= __GFP_NORETRY | __GFP_NOWARN;
+		bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ,
+				     gfp);
+		/*
+		 * If the bio_alloc fails, try it again for a single page to
+		 * avoid having to deal with partial page reads.  This emulates
+		 * what do_mpage_read_folio does.
+		 */
+		if (!bio)
+			bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
+		if (ctx->rac)
+			bio->bi_opf |= REQ_RAHEAD;
+		bio->bi_iter.bi_sector = sector;
+		bio->bi_end_io = iomap_read_end_io;
+		bio_add_folio_nofail(bio, folio, plen, poff);
+		ctx->read_ctx = bio;
+	}
+	return 0;
+}
+
+const struct iomap_read_ops iomap_bio_read_ops = {
+	.read_folio_range = iomap_bio_read_folio_range,
+	.submit_read = iomap_bio_submit_read,
+};
+EXPORT_SYMBOL_GPL(iomap_bio_read_ops);
+
+int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
+		struct folio *folio, loff_t pos, size_t len)
+{
+	const struct iomap *srcmap = iomap_iter_srcmap(iter);
+	struct bio_vec bvec;
+	struct bio bio;
+
+	bio_init(&bio, srcmap->bdev, &bvec, 1, REQ_OP_READ);
+	bio.bi_iter.bi_sector = iomap_sector(srcmap, pos);
+	bio_add_folio_nofail(&bio, folio, len, offset_in_folio(folio, pos));
+	return submit_bio_wait(&bio);
+}
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 667a49cb5ae5..72258b0109ec 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -8,6 +8,7 @@
 #include <linux/writeback.h>
 #include <linux/swap.h>
 #include <linux/migrate.h>
+#include "internal.h"
 #include "trace.h"
 
 #include "../internal.h"
@@ -352,74 +353,6 @@ void iomap_finish_folio_read(struct folio *folio, size_t off, size_t len,
 }
 EXPORT_SYMBOL_GPL(iomap_finish_folio_read);
 
-#ifdef CONFIG_BLOCK
-static void iomap_read_end_io(struct bio *bio)
-{
-	int error = blk_status_to_errno(bio->bi_status);
-	struct folio_iter fi;
-
-	bio_for_each_folio_all(fi, bio)
-		iomap_finish_folio_read(fi.folio, fi.offset, fi.length, error);
-	bio_put(bio);
-}
-
-static void iomap_bio_submit_read(struct iomap_read_folio_ctx *ctx)
-{
-	struct bio *bio = ctx->read_ctx;
-
-	if (bio)
-		submit_bio(bio);
-}
-
-static int iomap_bio_read_folio_range(const struct iomap_iter *iter,
-		struct iomap_read_folio_ctx *ctx, size_t plen)
-{
-	struct folio *folio = ctx->cur_folio;
-	const struct iomap *iomap = &iter->iomap;
-	loff_t pos = iter->pos;
-	size_t poff = offset_in_folio(folio, pos);
-	loff_t length = iomap_length(iter);
-	sector_t sector;
-	struct bio *bio = ctx->read_ctx;
-
-	iomap_start_folio_read(folio, plen);
-
-	sector = iomap_sector(iomap, pos);
-	if (!bio || bio_end_sector(bio) != sector ||
-	    !bio_add_folio(bio, folio, plen, poff)) {
-		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
-		gfp_t orig_gfp = gfp;
-		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
-
-		iomap_bio_submit_read(ctx);
-
-		if (ctx->rac) /* same as readahead_gfp_mask */
-			gfp |= __GFP_NORETRY | __GFP_NOWARN;
-		bio = bio_alloc(iomap->bdev, bio_max_segs(nr_vecs), REQ_OP_READ,
-				     gfp);
-		/*
-		 * If the bio_alloc fails, try it again for a single page to
-		 * avoid having to deal with partial page reads.  This emulates
-		 * what do_mpage_read_folio does.
-		 */
-		if (!bio)
-			bio = bio_alloc(iomap->bdev, 1, REQ_OP_READ, orig_gfp);
-		if (ctx->rac)
-			bio->bi_opf |= REQ_RAHEAD;
-		bio->bi_iter.bi_sector = sector;
-		bio->bi_end_io = iomap_read_end_io;
-		bio_add_folio_nofail(bio, folio, plen, poff);
-		ctx->read_ctx = bio;
-	}
-	return 0;
-}
-
-const struct iomap_read_ops iomap_bio_read_ops = {
-	.read_folio_range	= iomap_bio_read_folio_range,
-	.submit_read		= iomap_bio_submit_read,
-};
-EXPORT_SYMBOL_GPL(iomap_bio_read_ops);
-
 /*
  * Add a bias to ifs->read_bytes_pending to prevent the read on the folio from
  * being ended prematurely.
@@ -623,27 +556,6 @@ void iomap_readahead(const struct iomap_ops *ops,
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);
 
-static int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
-		struct folio *folio, loff_t pos, size_t len)
-{
-	const struct iomap *srcmap = iomap_iter_srcmap(iter);
-	struct bio_vec bvec;
-	struct bio bio;
-
-	bio_init(&bio, srcmap->bdev, &bvec, 1, REQ_OP_READ);
-	bio.bi_iter.bi_sector = iomap_sector(srcmap, pos);
-	bio_add_folio_nofail(&bio, folio, len, offset_in_folio(folio, pos));
-	return submit_bio_wait(&bio);
-}
-#else
-static int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
-		struct folio *folio, loff_t pos, size_t len)
-{
-	WARN_ON_ONCE(1);
-	return -EIO;
-}
-#endif /* CONFIG_BLOCK */
-
 /*
  * iomap_is_partially_uptodate checks whether blocks within a folio are
  * uptodate or not.
diff --git a/fs/iomap/internal.h b/fs/iomap/internal.h
index d05cb3aed96e..7ab1033ab4b7 100644
--- a/fs/iomap/internal.h
+++ b/fs/iomap/internal.h
@@ -6,4 +6,16 @@
 
 u32 iomap_finish_ioend_direct(struct iomap_ioend *ioend);
 
+#ifdef CONFIG_BLOCK
+int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
+		struct folio *folio, loff_t pos, size_t len);
+#else
+int iomap_bio_read_folio_range_sync(const struct iomap_iter *iter,
+		struct folio *folio, loff_t pos, size_t len)
+{
+	WARN_ON_ONCE(1);
+	return -EIO;
+}
+#endif /* CONFIG_BLOCK */
+
 #endif /* _IOMAP_INTERNAL_H */
-- 
2.47.3

No errors are propagated in iomap_read_folio(). Change
iomap_read_folio() to a void return to make this clearer to callers.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/iomap/buffered-io.c | 9 +--------
 include/linux/iomap.h  | 2 +-
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 72258b0109ec..be535bd3aeca 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -450,7 +450,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 	return ret;
 }
 
-int iomap_read_folio(const struct iomap_ops *ops,
+void iomap_read_folio(const struct iomap_ops *ops,
 		struct iomap_read_folio_ctx *ctx)
 {
 	struct folio *folio = ctx->cur_folio;
@@ -477,13 +477,6 @@ int iomap_read_folio(const struct iomap_ops *ops,
 
 	if (!cur_folio_owned)
 		folio_unlock(folio);
-
-	/*
-	 * Just like mpage_readahead and block_read_full_folio, we always
-	 * return 0 and just set the folio error flag on errors.  This
-	 * should be cleaned up throughout the stack eventually.
-	 */
-	return 0;
 }
 EXPORT_SYMBOL_GPL(iomap_read_folio);
 
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 4a168ebb40f5..fa55ec611fff 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -340,7 +340,7 @@ static inline bool iomap_want_unshare_iter(const struct iomap_iter *iter)
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops,
 		const struct iomap_write_ops *write_ops, void *private);
-int iomap_read_folio(const struct iomap_ops *ops,
+void iomap_read_folio(const struct iomap_ops *ops,
 		struct iomap_read_folio_ctx *ctx);
 void iomap_readahead(const struct iomap_ops *ops,
 		struct iomap_read_folio_ctx *ctx);
-- 
2.47.3

Read folio data into the page cache using iomap. This gives us granular
uptodate tracking for large folios, which optimizes how much data needs
to be read in. If some portions of the folio are already uptodate (eg
through a prior write), we only need to read in the non-uptodate
portions.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/fuse/file.c | 81 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 57 insertions(+), 24 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 4adcf09d4b01..4f27a3b0c20a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -828,23 +828,70 @@ static int fuse_do_readfolio(struct file *file, struct folio *folio,
 	return 0;
 }
 
+static int fuse_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+			    unsigned int flags, struct iomap *iomap,
+			    struct iomap *srcmap)
+{
+	iomap->type = IOMAP_MAPPED;
+	iomap->length = length;
+	iomap->offset = offset;
+	return 0;
+}
+
+static const struct iomap_ops fuse_iomap_ops = {
+	.iomap_begin	= fuse_iomap_begin,
+};
+
+struct fuse_fill_read_data {
+	struct file *file;
+};
+
+static int fuse_iomap_read_folio_range_async(const struct iomap_iter *iter,
+					     struct iomap_read_folio_ctx *ctx,
+					     size_t len)
+{
+	struct fuse_fill_read_data *data = ctx->read_ctx;
+	struct folio *folio = ctx->cur_folio;
+	loff_t pos =  iter->pos;
+	size_t off = offset_in_folio(folio, pos);
+	struct file *file = data->file;
+	int ret;
+
+	/*
+	 *  for non-readahead read requests, do reads synchronously since
+	 *  it's not guaranteed that the server can handle out-of-order reads
+	 */
+	iomap_start_folio_read(folio, len);
+	ret = fuse_do_readfolio(file, folio, off, len);
+	iomap_finish_folio_read(folio, off, len, ret);
+	return ret;
+}
+
+static const struct iomap_read_ops fuse_iomap_read_ops = {
+	.read_folio_range = fuse_iomap_read_folio_range_async,
+};
+
 static int fuse_read_folio(struct file *file, struct folio *folio)
 {
 	struct inode *inode = folio->mapping->host;
-	int err;
+	struct fuse_fill_read_data data = {
+		.file = file,
+	};
+	struct iomap_read_folio_ctx ctx = {
+		.cur_folio = folio,
+		.ops = &fuse_iomap_read_ops,
+		.read_ctx = &data,
 
-	err = -EIO;
-	if (fuse_is_bad(inode))
-		goto out;
+	};
 
-	err = fuse_do_readfolio(file, folio, 0, folio_size(folio));
-	if (!err)
-		folio_mark_uptodate(folio);
+	if (fuse_is_bad(inode)) {
+		folio_unlock(folio);
+		return -EIO;
+	}
 
+	iomap_read_folio(&fuse_iomap_ops, &ctx);
 	fuse_invalidate_atime(inode);
- out:
-	folio_unlock(folio);
-	return err;
+	return 0;
 }
 
 static int fuse_iomap_read_folio_range(const struct iomap_iter *iter,
@@ -1394,20 +1441,6 @@ static const struct iomap_write_ops fuse_iomap_write_ops = {
 	.read_folio_range = fuse_iomap_read_folio_range,
 };
 
-static int fuse_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
-			    unsigned int flags, struct iomap *iomap,
-			    struct iomap *srcmap)
-{
-	iomap->type = IOMAP_MAPPED;
-	iomap->length = length;
-	iomap->offset = offset;
-	return 0;
-}
-
-static const struct iomap_ops fuse_iomap_ops = {
-	.iomap_begin	= fuse_iomap_begin,
-};
-
 static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
-- 
2.47.3

Do readahead in fuse using iomap. This gives us granular uptodate
tracking for large folios, which optimizes how much data needs to be
read in. If some portions of the folio are already uptodate (eg through
a prior write), we only need to read in the non-uptodate portions.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/fuse/file.c | 220 ++++++++++++++++++++++++++++---------------------
 1 file changed, 124 insertions(+), 96 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 4f27a3b0c20a..db0b1f20fee4 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -844,8 +844,65 @@ static const struct iomap_ops fuse_iomap_ops = {
 
 struct fuse_fill_read_data {
 	struct file *file;
+
+	/* Fields below are used if sending the read request asynchronously */
+	struct fuse_conn *fc;
+	struct fuse_io_args *ia;
+	unsigned int nr_bytes;
 };
 
+/* forward declarations */
+static bool fuse_folios_need_send(struct fuse_conn *fc, loff_t pos,
+				  unsigned len, struct fuse_args_pages *ap,
+				  unsigned cur_bytes, bool write);
+static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
+				unsigned int count, bool async);
+
+static int fuse_handle_readahead(struct folio *folio,
+				 struct readahead_control *rac,
+				 struct fuse_fill_read_data *data, loff_t pos,
+				 size_t len)
+{
+	struct fuse_io_args *ia = data->ia;
+	size_t off = offset_in_folio(folio, pos);
+	struct fuse_conn *fc = data->fc;
+	struct fuse_args_pages *ap;
+	unsigned int nr_pages;
+
+	if (ia && fuse_folios_need_send(fc, pos, len, &ia->ap, data->nr_bytes,
+					false)) {
+		fuse_send_readpages(ia, data->file, data->nr_bytes,
+				    fc->async_read);
+		data->nr_bytes = 0;
+		data->ia = NULL;
+		ia = NULL;
+	}
+	if (!ia) {
+		if (fc->num_background >= fc->congestion_threshold &&
+		    rac->ra->async_size >= readahead_count(rac))
+			/*
+			 * Congested and only async pages left, so skip the
+			 * rest.
+			 */
+			return -EAGAIN;
+
+		nr_pages = min(fc->max_pages, readahead_count(rac));
+		data->ia = fuse_io_alloc(NULL, nr_pages);
+		if (!data->ia)
+			return -ENOMEM;
+		ia = data->ia;
+	}
+	folio_get(folio);
+	ap = &ia->ap;
+	ap->folios[ap->num_folios] = folio;
+	ap->descs[ap->num_folios].offset = off;
+	ap->descs[ap->num_folios].length = len;
+	data->nr_bytes += len;
+	ap->num_folios++;
+
+	return 0;
+}
+
 static int fuse_iomap_read_folio_range_async(const struct iomap_iter *iter,
 					     struct iomap_read_folio_ctx *ctx,
 					     size_t len)
@@ -857,18 +914,40 @@ static int fuse_iomap_read_folio_range_async(const struct iomap_iter *iter,
 	struct file *file = data->file;
 	int ret;
 
-	/*
-	 *  for non-readahead read requests, do reads synchronously since
-	 *  it's not guaranteed that the server can handle out-of-order reads
-	 */
 	iomap_start_folio_read(folio, len);
-	ret = fuse_do_readfolio(file, folio, off, len);
-	iomap_finish_folio_read(folio, off, len, ret);
+	if (ctx->rac) {
+		ret = fuse_handle_readahead(folio, ctx->rac, data, pos, len);
+		/*
+		 * If fuse_handle_readahead was successful, fuse_readpages_end
+		 * will do the iomap_finish_folio_read, else we need to call it
+		 * here
+		 */
+		if (ret)
+			iomap_finish_folio_read(folio, off, len, ret);
+	} else {
+		/*
+		 *  for non-readahead read requests, do reads synchronously
+		 *  since it's not guaranteed that the server can handle
+		 *  out-of-order reads
+		 */
+		ret = fuse_do_readfolio(file, folio, off, len);
+		iomap_finish_folio_read(folio, off, len, ret);
+	}
 	return ret;
 }
 
+static void fuse_iomap_read_submit(struct iomap_read_folio_ctx *ctx)
+{
+	struct fuse_fill_read_data *data = ctx->read_ctx;
+
+	if (data->ia)
+		fuse_send_readpages(data->ia, data->file, data->nr_bytes,
+				    data->fc->async_read);
+}
+
 static const struct iomap_read_ops fuse_iomap_read_ops = {
 	.read_folio_range = fuse_iomap_read_folio_range_async,
+	.submit_read = fuse_iomap_read_submit,
 };
 
 static int fuse_read_folio(struct file *file, struct folio *folio)
@@ -930,7 +1009,8 @@ static void fuse_readpages_end(struct fuse_mount *fm, struct fuse_args *args,
 	}
 
 	for (i = 0; i < ap->num_folios; i++) {
-		folio_end_read(ap->folios[i], !err);
+		iomap_finish_folio_read(ap->folios[i], ap->descs[i].offset,
+					ap->descs[i].length, err);
 		folio_put(ap->folios[i]);
 	}
 	if (ia->ff)
@@ -940,7 +1020,7 @@ static void fuse_readpages_end(struct fuse_mount *fm, struct fuse_args *args,
 }
 
 static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
-				unsigned int count)
+				unsigned int count, bool async)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_mount *fm = ff->fm;
@@ -962,7 +1042,7 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
 
 	fuse_read_args_fill(ia, file, pos, count, FUSE_READ);
 	ia->read.attr_ver = fuse_get_attr_version(fm->fc);
-	if (fm->fc->async_read) {
+	if (async) {
 		ia->ff = fuse_file_get(ff);
 		ap->args.end = fuse_readpages_end;
 		err = fuse_simple_background(fm, &ap->args, GFP_KERNEL);
@@ -979,81 +1059,20 @@ static void fuse_readahead(struct readahead_control *rac)
 {
 	struct inode *inode = rac->mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	unsigned int max_pages, nr_pages;
-	struct folio *folio = NULL;
+	struct fuse_fill_read_data data = {
+		.file = rac->file,
+		.fc = fc,
+	};
+	struct iomap_read_folio_ctx ctx = {
+		.ops = &fuse_iomap_read_ops,
+		.rac = rac,
+		.read_ctx = &data
+	};
 
 	if (fuse_is_bad(inode))
 		return;
 
-	max_pages = min_t(unsigned int, fc->max_pages,
-			fc->max_read / PAGE_SIZE);
-
-	/*
-	 * This is only accurate the first time through, since readahead_folio()
-	 * doesn't update readahead_count() from the previous folio until the
-	 * next call.  Grab nr_pages here so we know how many pages we're going
-	 * to have to process.  This means that we will exit here with
-	 * readahead_count() == folio_nr_pages(last_folio), but we will have
-	 * consumed all of the folios, and read_pages() will call
-	 * readahead_folio() again which will clean up the rac.
-	 */
-	nr_pages = readahead_count(rac);
-
-	while (nr_pages) {
-		struct fuse_io_args *ia;
-		struct fuse_args_pages *ap;
-		unsigned cur_pages = min(max_pages, nr_pages);
-		unsigned int pages = 0;
-
-		if (fc->num_background >= fc->congestion_threshold &&
-		    rac->ra->async_size >= readahead_count(rac))
-			/*
-			 * Congested and only async pages left, so skip the
-			 * rest.
-			 */
-			break;
-
-		ia = fuse_io_alloc(NULL, cur_pages);
-		if (!ia)
-			break;
-		ap = &ia->ap;
-
-		while (pages < cur_pages) {
-			unsigned int folio_pages;
-
-			/*
-			 * This returns a folio with a ref held on it.
-			 * The ref needs to be held until the request is
-			 * completed, since the splice case (see
-			 * fuse_try_move_page()) drops the ref after it's
-			 * replaced in the page cache.
-			 */
-			if (!folio)
-				folio =  __readahead_folio(rac);
-
-			folio_pages = folio_nr_pages(folio);
-			if (folio_pages > cur_pages - pages) {
-				/*
-				 * Large folios belonging to fuse will never
-				 * have more pages than max_pages.
-				 */
-				WARN_ON(!pages);
-				break;
-			}
-
-			ap->folios[ap->num_folios] = folio;
-			ap->descs[ap->num_folios].length = folio_size(folio);
-			ap->num_folios++;
-			pages += folio_pages;
-			folio = NULL;
-		}
-		fuse_send_readpages(ia, rac->file, pages << PAGE_SHIFT);
-		nr_pages -= pages;
-	}
-	if (folio) {
-		folio_end_read(folio, false);
-		folio_put(folio);
-	}
+	iomap_readahead(&fuse_iomap_ops, &ctx);
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
@@ -2084,7 +2103,7 @@ struct fuse_fill_wb_data {
 	struct fuse_file *ff;
 	unsigned int max_folios;
 	/*
-	 * nr_bytes won't overflow since fuse_writepage_need_send() caps
+	 * nr_bytes won't overflow since fuse_folios_need_send() caps
 	 * wb requests to never exceed fc->max_pages (which has an upper bound
 	 * of U16_MAX).
 	 */
@@ -2129,14 +2148,15 @@ static void fuse_writepages_send(struct inode *inode,
 	spin_unlock(&fi->lock);
 }
 
-static bool fuse_writepage_need_send(struct fuse_conn *fc, loff_t pos,
-				     unsigned len, struct fuse_args_pages *ap,
-				     struct fuse_fill_wb_data *data)
+static bool fuse_folios_need_send(struct fuse_conn *fc, loff_t pos,
+				  unsigned len, struct fuse_args_pages *ap,
+				  unsigned cur_bytes, bool write)
 {
 	struct folio *prev_folio;
 	struct fuse_folio_desc prev_desc;
-	unsigned bytes = data->nr_bytes + len;
+	unsigned bytes = cur_bytes + len;
 	loff_t prev_pos;
+	size_t max_bytes = write ? fc->max_write : fc->max_read;
 
 	WARN_ON(!ap->num_folios);
 
@@ -2144,8 +2164,7 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, loff_t pos,
 	if ((bytes + PAGE_SIZE - 1) >> PAGE_SHIFT > fc->max_pages)
 		return true;
 
-	/* Reached max write bytes */
-	if (bytes > fc->max_write)
+	if (bytes > max_bytes)
 		return true;
 
 	/* Discontinuity */
@@ -2155,11 +2174,6 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, loff_t pos,
 	if (prev_pos != pos)
 		return true;
 
-	/* Need to grow the pages array?  If so, did the expansion fail? */
-	if (ap->num_folios == data->max_folios &&
-	    !fuse_pages_realloc(data, fc->max_pages))
-		return true;
-
 	return false;
 }
 
@@ -2183,10 +2197,24 @@ static ssize_t fuse_iomap_writeback_range(struct iomap_writepage_ctx *wpc,
 			return -EIO;
 	}
 
-	if (wpa && fuse_writepage_need_send(fc, pos, len, ap, data)) {
-		fuse_writepages_send(inode, data);
-		data->wpa = NULL;
-		data->nr_bytes = 0;
+	if (wpa) {
+		bool send = fuse_folios_need_send(fc, pos, len, ap,
+						  data->nr_bytes, true);
+
+		if (!send) {
+			/*
+			 * Need to grow the pages array?  If so, did the
+			 * expansion fail?
+			 */
+			send = (ap->num_folios == data->max_folios) &&
+				!fuse_pages_realloc(data, fc->max_pages);
+		}
+
+		if (send) {
+			fuse_writepages_send(inode, data);
+			data->wpa = NULL;
+			data->nr_bytes = 0;
+		}
 	}
 
 	if (data->wpa == NULL) {
-- 
2.47.3

Now that fuse is integrated with iomap for read/readahead, we can remove
the workaround that was added in commit bd24d2108e9c ("fuse: fix fuseblk
i_blkbits for iomap partial writes"), which was previously needed to
avoid a race condition where an iomap partial write may be overwritten
by a read if blocksize < PAGE_SIZE. Now that fuse does iomap
read/readahead, this is protected against since there is granular
uptodate tracking of blocks, which means this workaround can be removed.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/fuse/dir.c    |  2 +-
 fs/fuse/fuse_i.h |  8 --------
 fs/fuse/inode.c  | 13 +------------
 3 files changed, 2 insertions(+), 21 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 5c569c3cb53f..ebee7e0b1cd3 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1199,7 +1199,7 @@ static void fuse_fillattr(struct mnt_idmap *idmap, struct inode *inode,
 	if (attr->blksize != 0)
 		blkbits = ilog2(attr->blksize);
 	else
-		blkbits = fc->blkbits;
+		blkbits = inode->i_sb->s_blocksize_bits;
 
 	stat->blksize = 1 << blkbits;
 }
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index cc428d04be3e..1647eb7ca6fa 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -975,14 +975,6 @@ struct fuse_conn {
 		/* Request timeout (in jiffies). 0 = no timeout */
 		unsigned int req_timeout;
 	} timeout;
-
-	/*
-	 * This is a workaround until fuse uses iomap for reads.
-	 * For fuseblk servers, this represents the blocksize passed in at
-	 * mount time and for regular fuse servers, this is equivalent to
-	 * inode->i_blkbits.
-	 */
-	u8 blkbits;
 };
 
 /*
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index fdecd5a90dee..5899a47faaef 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -292,7 +292,7 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
 	if (attr->blksize)
 		fi->cached_i_blkbits = ilog2(attr->blksize);
 	else
-		fi->cached_i_blkbits = fc->blkbits;
+		fi->cached_i_blkbits = inode->i_sb->s_blocksize_bits;
 
 	/*
 	 * Don't set the sticky bit in i_mode, unless we want the VFS
@@ -1810,21 +1810,10 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 		err = -EINVAL;
 		if (!sb_set_blocksize(sb, ctx->blksize))
 			goto err;
-		/*
-		 * This is a workaround until fuse hooks into iomap for reads.
-		 * Use PAGE_SIZE for the blocksize else if the writeback cache
-		 * is enabled, buffered writes go through iomap and a read may
-		 * overwrite partially written data if blocksize < PAGE_SIZE
-		 */
-		fc->blkbits = sb->s_blocksize_bits;
-		if (ctx->blksize != PAGE_SIZE &&
-		    !sb_set_blocksize(sb, PAGE_SIZE))
-			goto err;
 #endif
 	} else {
 		sb->s_blocksize = PAGE_SIZE;
 		sb->s_blocksize_bits = PAGE_SHIFT;
-		fc->blkbits = sb->s_blocksize_bits;
 	}
 
 	sb->s_subtype = ctx->subtype;
-- 
2.47.3