[PATCH v4 04/15] iomap: iterate over folio mapping in iomap_readpage_iter()

[Joanne Koong <joannelkoong@xxxxxxxxx>]

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

Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 53 ++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 28 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index b06b532033ad..dbe5783ee68c 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -430,6 +430,7 @@ 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) {
@@ -439,41 +440,35 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 		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);
-	}
+	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);
+		/* zero post-eof blocks as the page may be mapped */
+		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);
+		}
+
+		ret = iomap_iter_advance(iter, count);
 		if (ret)
 			return ret;
+		length -= count;
+		pos = iter->pos;
 	}
-
 	return 0;
 }
 
@@ -492,7 +487,7 @@ 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);
 
@@ -522,6 +517,8 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
 		}
 		if (!ctx->cur_folio) {
 			ctx->cur_folio = readahead_folio(ctx->rac);
+			if (WARN_ON_ONCE(!ctx->cur_folio))
+				return -EINVAL;
 			ctx->cur_folio_in_bio = false;
 		}
 		ret = iomap_readpage_iter(iter, ctx);
-- 
2.47.3