ext4, fscrypt: merge fscrypt_mergeable_bio_bh into io_submit_need_new_bio

ext4 already has the inode and folio and can't have a NULL
folio->mapping in this path. Open code fscrypt_mergeable_bio_bh in
io_submit_need_new_bio based on these simplifying assumptions.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20260302141922.370070-5-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Christoph Hellwig

fs/crypto/inline_crypt.c

@@ -406,29 +406,6 @@ bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
 
-/**
- * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
- * @bio: the bio being built up
- * @next_bh: the next buffer_head for which I/O will be submitted
- *
- * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
- * an inode and block number directly.
- *
- * Return: true iff the I/O is mergeable
- */
-bool fscrypt_mergeable_bio_bh(struct bio *bio,
-			      const struct buffer_head *next_bh)
-{
-	const struct inode *inode;
-	u64 next_lblk;
-
-	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
-		return !bio->bi_crypt_context;
-
-	return fscrypt_mergeable_bio(bio, inode, next_lblk);
-}
-EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
-
 /**
  * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an
  *			     inode, as far as encryption is concerned

fs/ext4/page-io.c

@@ -440,11 +440,14 @@ static void io_submit_init_bio(struct ext4_io_submit *io,
 }
 
 static bool io_submit_need_new_bio(struct ext4_io_submit *io,
+				   struct inode *inode,
+				   struct folio *folio,
 				   struct buffer_head *bh)
 {
 	if (bh->b_blocknr != io->io_next_block)
 		return true;
-	if (!fscrypt_mergeable_bio_bh(io->io_bio, bh))
+	if (!fscrypt_mergeable_bio(io->io_bio, inode,
+			(folio_pos(folio) + bh_offset(bh)) >> inode->i_blkbits))
 		return true;
 	return false;
 }
@@ -455,7 +458,7 @@ static void io_submit_add_bh(struct ext4_io_submit *io,
 			     struct folio *io_folio,
 			     struct buffer_head *bh)
 {
-	if (io->io_bio && io_submit_need_new_bio(io, bh)) {
+	if (io->io_bio && io_submit_need_new_bio(io, inode, folio, bh)) {
 submit_and_retry:
 		ext4_io_submit(io);
 	}

include/linux/fscrypt.h

@@ -876,9 +876,6 @@ void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 			   u64 next_lblk);
 
-bool fscrypt_mergeable_bio_bh(struct bio *bio,
-			      const struct buffer_head *next_bh);
-
 bool fscrypt_dio_supported(struct inode *inode);
 
 u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks);
@@ -906,12 +903,6 @@ static inline bool fscrypt_mergeable_bio(struct bio *bio,
 	return true;
 }
 
-static inline bool fscrypt_mergeable_bio_bh(struct bio *bio,
-					    const struct buffer_head *next_bh)
-{
-	return true;
-}
-
 static inline bool fscrypt_dio_supported(struct inode *inode)
 {
 	return !fscrypt_needs_contents_encryption(inode);