fs-verity: add inode and superblock fields

Analogous to fs/crypto/, add fields to the VFS inode and superblock for
use by the fs/verity/ support layer:

- ->s_vop: points to the fsverity_operations if the filesystem supports
  fs-verity, otherwise is NULL.

- ->i_verity_info: points to cached fs-verity information for the inode
  after someone opens it, otherwise is NULL.

- S_VERITY: bit in ->i_flags that identifies verity inodes, even when
  they haven't been opened yet and thus still have NULL ->i_verity_info.
Reviewed-by: NTheodore Ts'o <tytso@mit.edu>
Reviewed-by: NJaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: NEric Biggers <ebiggers@google.com>

include/linux/fs.h

@@ -64,6 +64,8 @@ struct workqueue_struct;
 struct iov_iter;
 struct fscrypt_info;
 struct fscrypt_operations;
+struct fsverity_info;
+struct fsverity_operations;
 struct fs_context;
 struct fs_parameter_description;
 
@@ -723,6 +725,10 @@ struct inode {
 	struct fscrypt_info	*i_crypt_info;
 #endif
 
+#ifdef CONFIG_FS_VERITY
+	struct fsverity_info	*i_verity_info;
+#endif
+
 	void			*i_private; /* fs or device private pointer */
 } __randomize_layout;
 
@@ -1427,6 +1433,9 @@ struct super_block {
 	const struct xattr_handler **s_xattr;
 #ifdef CONFIG_FS_ENCRYPTION
 	const struct fscrypt_operations	*s_cop;
+#endif
+#ifdef CONFIG_FS_VERITY
+	const struct fsverity_operations *s_vop;
 #endif
 	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
@@ -1965,6 +1974,7 @@ struct super_operations {
 #endif
 #define S_ENCRYPTED	16384	/* Encrypted file (using fs/crypto/) */
 #define S_CASEFOLD	32768	/* Casefolded file */
+#define S_VERITY	65536	/* Verity file (using fs/verity/) */
 
 /*
  * Note that nosuid etc flags are inode-specific: setting some file-system
@@ -2006,6 +2016,7 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 #define IS_DAX(inode)		((inode)->i_flags & S_DAX)
 #define IS_ENCRYPTED(inode)	((inode)->i_flags & S_ENCRYPTED)
 #define IS_CASEFOLDED(inode)	((inode)->i_flags & S_CASEFOLD)
+#define IS_VERITY(inode)	((inode)->i_flags & S_VERITY)
 
 #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
 				 (inode)->i_rdev == WHITEOUT_DEV)