fsverity: optimize fsverity_file_open() on non-verity files

Make fsverity_file_open() an inline function that does the IS_VERITY()
check, then (if needed) calls __fsverity_file_open() to do the real
work.  This reduces the overhead on non-verity files.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Dave Chinner <dchinner@redhat.com>
Link: https://lore.kernel.org/r/20221214224304.145712-2-ebiggers@kernel.org

fs/verity/open.c

@@ -325,24 +325,8 @@ static int ensure_verity_info(struct inode *inode)
 	return err;
 }
 
-/**
- * fsverity_file_open() - prepare to open a verity file
- * @inode: the inode being opened
- * @filp: the struct file being set up
- *
- * When opening a verity file, deny the open if it is for writing.  Otherwise,
- * set up the inode's ->i_verity_info if not already done.
- *
- * When combined with fscrypt, this must be called after fscrypt_file_open().
- * Otherwise, we won't have the key set up to decrypt the verity metadata.
- *
- * Return: 0 on success, -errno on failure
- */
-int fsverity_file_open(struct inode *inode, struct file *filp)
+int __fsverity_file_open(struct inode *inode, struct file *filp)
 {
-	if (!IS_VERITY(inode))
-		return 0;
-
 	if (filp->f_mode & FMODE_WRITE) {
 		pr_debug("Denying opening verity file (ino %lu) for write\n",
 			 inode->i_ino);
@@ -351,7 +335,7 @@ int fsverity_file_open(struct inode *inode, struct file *filp)
 
 	return ensure_verity_info(inode);
 }
-EXPORT_SYMBOL_GPL(fsverity_file_open);
+EXPORT_SYMBOL_GPL(__fsverity_file_open);
 
 /**
  * fsverity_prepare_setattr() - prepare to change a verity inode's attributes

include/linux/fsverity.h

@@ -148,7 +148,7 @@ int fsverity_get_digest(struct inode *inode,
 
 /* open.c */
 
-int fsverity_file_open(struct inode *inode, struct file *filp);
+int __fsverity_file_open(struct inode *inode, struct file *filp);
 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 void fsverity_cleanup_inode(struct inode *inode);
 
@@ -193,9 +193,9 @@ static inline int fsverity_get_digest(struct inode *inode,
 
 /* open.c */
 
-static inline int fsverity_file_open(struct inode *inode, struct file *filp)
+static inline int __fsverity_file_open(struct inode *inode, struct file *filp)
 {
-	return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
+	return -EOPNOTSUPP;
 }
 
 static inline int fsverity_prepare_setattr(struct dentry *dentry,
@@ -254,4 +254,24 @@ static inline bool fsverity_active(const struct inode *inode)
 	return fsverity_get_info(inode) != NULL;
 }
 
+/**
+ * fsverity_file_open() - prepare to open a verity file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * When opening a verity file, deny the open if it is for writing.  Otherwise,
+ * set up the inode's ->i_verity_info if not already done.
+ *
+ * When combined with fscrypt, this must be called after fscrypt_file_open().
+ * Otherwise, we won't have the key set up to decrypt the verity metadata.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static inline int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+	if (IS_VERITY(inode))
+		return __fsverity_file_open(inode, filp);
+	return 0;
+}
+
 #endif	/* _LINUX_FSVERITY_H */