[PATCH v4 07/15] iomap: track read/readahead folio ownership internally

[Joanne Koong <joannelkoong@gmail.com>]

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 09e65771a947..34df1cddf65c 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -362,7 +362,6 @@ 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;
 };
@@ -386,7 +385,6 @@ 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;
@@ -423,7 +421,7 @@ 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 *folio_owned)
 {
 	const struct iomap *iomap = &iter->iomap;
 	loff_t pos = iter->pos;
@@ -460,6 +458,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
 			folio_zero_range(folio, poff, plen);
 			iomap_set_range_uptodate(folio, poff, plen);
 		} else {
+			*folio_owned = true;
 			iomap_bio_read_folio_range(iter, ctx, pos, plen);
 		}
 
@@ -482,16 +481,22 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	struct iomap_read_folio_ctx ctx = {
 		.cur_folio	= folio,
 	};
+	/*
+	 * If an IO helper takes ownership of the folio, it is responsible for
+	 * unlocking it when the read completes.
+	 */
+	bool 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,
+				&folio_owned);
 
 	iomap_bio_submit_read(&ctx);
 
-	if (!ctx.cur_folio_in_bio)
+	if (!folio_owned)
 		folio_unlock(folio);
 
 	/*
@@ -504,14 +509,15 @@ 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 &&
 		    offset_in_folio(ctx->cur_folio, iter->pos) == 0) {
-			if (!ctx->cur_folio_in_bio)
+			if (!*cur_folio_owned)
 				folio_unlock(ctx->cur_folio);
 			ctx->cur_folio = NULL;
 		}
@@ -519,9 +525,9 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 			ctx->cur_folio = readahead_folio(ctx->rac);
 			if (WARN_ON_ONCE(!ctx->cur_folio))
 				return -EINVAL;
-			ctx->cur_folio_in_bio = false;
+			*cur_folio_owned = false;
 		}
-		ret = iomap_read_folio_iter(iter, ctx);
+		ret = iomap_read_folio_iter(iter, ctx, cur_folio_owned);
 		if (ret)
 			return ret;
 	}
@@ -554,15 +560,21 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 	struct iomap_read_folio_ctx ctx = {
 		.rac	= rac,
 	};
+	/*
+	 * If an 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