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>
---
 fs/iomap/buffered-io.c | 67 ++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 38 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 51d204f0e077..fc8fa24ae7db 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -431,6 +431,7 @@ 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) {
@@ -442,39 +443,29 @@ 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_read_folio_range_bio_async(iter, ctx, pos, 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);
-}
+	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);
+		count = pos - iter->pos + plen;
+		if (plen == 0)
+			return iomap_iter_advance(iter, &count);
 
-static int iomap_read_folio_iter(struct iomap_iter *iter,
-		struct iomap_readpage_ctx *ctx)
-{
-	int ret;
+		if (iomap_block_needs_zeroing(iter, pos)) {
+			folio_zero_range(folio, poff, plen);
+			iomap_set_range_uptodate(folio, poff, plen);
+		} else {
+			iomap_read_folio_range_bio_async(iter, ctx, pos, plen);
+		}
 
-	while (iomap_length(iter)) {
-		ret = iomap_readpage_iter(iter, ctx);
+		length -= count;
+		ret = iomap_iter_advance(iter, &count);
 		if (ret)
 			return ret;
+		pos = iter->pos;
 	}
-
 	return 0;
 }
 
@@ -493,7 +484,7 @@ 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_submit_read_bio(&ctx);
 
@@ -510,16 +501,16 @@ 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->folio_owned)
-				folio_unlock(ctx->cur_folio);
-			ctx->cur_folio = NULL;
-		}
-		if (!ctx->cur_folio) {
-			ctx->cur_folio = readahead_folio(ctx->rac);
-			ctx->folio_owned = false;
-		}
+		if (ctx->cur_folio && !ctx->folio_owned)
+			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->folio_owned = false;
 		ret = iomap_readpage_iter(iter, ctx);
 		if (ret)
 			return ret;
-- 
2.47.3