ubifs: move crypt info pointer to fs-specific part of inode

Move the fscrypt_inode_info pointer into the filesystem-specific part of
the inode by adding the field ubifs_inode::i_crypt_info and configuring
fscrypt_operations::inode_info_offs accordingly.

This is a prerequisite for a later commit that removes
inode::i_crypt_info, saving memory and improving cache efficiency with
filesystems that don't support fscrypt.

Note that the initialization of ubifs_inode::i_crypt_info to NULL on
inode allocation is handled by the memset() in ubifs_alloc_inode().

Co-developed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Link: https://lore.kernel.org/20250810075706.172910-6-ebiggers@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Eric Biggers

fs/ubifs/crypto.c

@@ -88,6 +88,8 @@ int ubifs_decrypt(const struct inode *inode, struct ubifs_data_node *dn,
 }
 
 const struct fscrypt_operations ubifs_crypt_operations = {
+	.inode_info_offs	= (int)offsetof(struct ubifs_inode, i_crypt_info) -
+				  (int)offsetof(struct ubifs_inode, vfs_inode),
 	.legacy_key_prefix	= "ubifs:",
 	.get_context		= ubifs_crypt_get_context,
 	.set_context		= ubifs_crypt_set_context,

fs/ubifs/ubifs.h

@@ -365,6 +365,7 @@ struct ubifs_gced_idx_leb {
  * @read_in_a_row: number of consecutive pages read in a row (for bulk read)
  * @data_len: length of the data attached to the inode
  * @data: inode's data
+ * @i_crypt_info: inode's fscrypt information
  *
  * @ui_mutex exists for two main reasons. At first it prevents inodes from
  * being written back while UBIFS changing them, being in the middle of an VFS
@@ -416,6 +417,9 @@ struct ubifs_inode {
 	pgoff_t read_in_a_row;
 	int data_len;
 	void *data;
+#ifdef CONFIG_FS_ENCRYPTION
+	struct fscrypt_inode_info *i_crypt_info;
+#endif
 };
 
 /**