fscrypt: move fscrypt_set_bio_crypt_ctx_bh to buffer.c

fscrypt_set_bio_crypt_ctx_bh is only used by submit_bh_wbc now.  Move it
there and merge bh_get_inode_and_lblk_num into it.

Note that this does not add ifdefs for fscrypt as the compiler will
optimize away the dead code if it is not built in.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20260302141922.370070-6-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Christoph Hellwig

fs/buffer.c

@@ -2774,6 +2774,24 @@ static void end_bio_bh_io_sync(struct bio *bio)
 	bio_put(bio);
 }
 
+static void buffer_set_crypto_ctx(struct bio *bio, const struct buffer_head *bh,
+				  gfp_t gfp_mask)
+{
+	const struct address_space *mapping = folio_mapping(bh->b_folio);
+	const struct inode *inode;
+	u64 lblk;
+
+	/*
+	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
+	 * for a non-pagecache page.  fscrypt doesn't care about these.
+	 */
+	if (!mapping)
+		return;
+	inode = mapping->host;
+	lblk = (folio_pos(bh->b_folio) + bh_offset(bh)) >> inode->i_blkbits;
+	fscrypt_set_bio_crypt_ctx(bio, inode, lblk, gfp_mask);
+}
+
 static void submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh,
 			  enum rw_hint write_hint,
 			  struct writeback_control *wbc)
@@ -2800,7 +2818,8 @@ static void submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh,
 
 	bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO);
 
-	fscrypt_set_bio_crypt_ctx_bh(bio, bh, GFP_NOIO);
+	if (IS_ENABLED(CONFIG_FS_ENCRYPTION))
+		buffer_set_crypto_ctx(bio, bh, GFP_NOIO);
 
 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 	bio->bi_write_hint = write_hint;

fs/crypto/inline_crypt.c

@@ -314,51 +314,6 @@ void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
 
-/* Extract the inode and logical block number from a buffer_head. */
-static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
-				      const struct inode **inode_ret,
-				      u64 *lblk_num_ret)
-{
-	struct folio *folio = bh->b_folio;
-	const struct address_space *mapping;
-	const struct inode *inode;
-
-	/*
-	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
-	 * for a non-pagecache page.  fscrypt doesn't care about these.
-	 */
-	mapping = folio_mapping(folio);
-	if (!mapping)
-		return false;
-	inode = mapping->host;
-
-	*inode_ret = inode;
-	*lblk_num_ret = (folio_pos(folio) + bh_offset(bh)) >> inode->i_blkbits;
-	return true;
-}
-
-/**
- * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
- *				    crypto
- * @bio: a bio which will eventually be submitted to the file
- * @first_bh: the first buffer_head for which I/O will be submitted
- * @gfp_mask: memory allocation flags
- *
- * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
- * of an inode and block number directly.
- */
-void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
-				  const struct buffer_head *first_bh,
-				  gfp_t gfp_mask)
-{
-	const struct inode *inode;
-	u64 first_lblk;
-
-	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
-		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
-}
-EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
-
 /**
  * fscrypt_mergeable_bio() - test whether data can be added to a bio
  * @bio: the bio being built up

include/linux/fscrypt.h

@@ -869,10 +869,6 @@ void fscrypt_set_bio_crypt_ctx(struct bio *bio,
 			       const struct inode *inode, u64 first_lblk,
 			       gfp_t gfp_mask);
 
-void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
-				  const struct buffer_head *first_bh,
-				  gfp_t gfp_mask);
-
 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 			   u64 next_lblk);
 
@@ -891,11 +887,6 @@ static inline void fscrypt_set_bio_crypt_ctx(struct bio *bio,
 					     const struct inode *inode,
 					     u64 first_lblk, gfp_t gfp_mask) { }
 
-static inline void fscrypt_set_bio_crypt_ctx_bh(
-					 struct bio *bio,
-					 const struct buffer_head *first_bh,
-					 gfp_t gfp_mask) { }
-
 static inline bool fscrypt_mergeable_bio(struct bio *bio,
 					 const struct inode *inode,
 					 u64 next_lblk)