fscrypt: move body of fscrypt_prepare_setattr() out-of-line

In preparation for reducing the visibility of fscrypt_require_key() by
moving it to fscrypt_private.h, move the call to it from
fscrypt_prepare_setattr() to an out-of-line function.
Reviewed-by: NAndreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20201203022041.230976-7-ebiggers@kernel.orgSigned-off-by: NEric Biggers <ebiggers@google.com>

fs/crypto/hooks.c

@@ -120,6 +120,14 @@ int __fscrypt_prepare_readdir(struct inode *dir)
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
 
+int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	if (attr->ia_valid & ATTR_SIZE)
+		return fscrypt_require_key(d_inode(dentry));
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr);
+
 /**
  * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
  * @inode: the inode on which flags are being changed

include/linux/fscrypt.h

@@ -243,6 +243,7 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 			     struct fscrypt_name *fname);
 int __fscrypt_prepare_readdir(struct inode *dir);
+int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 int fscrypt_prepare_setflags(struct inode *inode,
 			     unsigned int oldflags, unsigned int flags);
 int fscrypt_prepare_symlink(struct inode *dir, const char *target,
@@ -543,6 +544,12 @@ static inline int __fscrypt_prepare_readdir(struct inode *dir)
 	return -EOPNOTSUPP;
 }
 
+static inline int __fscrypt_prepare_setattr(struct dentry *dentry,
+					    struct iattr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int fscrypt_prepare_setflags(struct inode *inode,
 					   unsigned int oldflags,
 					   unsigned int flags)
@@ -840,8 +847,8 @@ static inline int fscrypt_prepare_readdir(struct inode *dir)
 static inline int fscrypt_prepare_setattr(struct dentry *dentry,
 					  struct iattr *attr)
 {
-	if (attr->ia_valid & ATTR_SIZE)
-		return fscrypt_require_key(d_inode(dentry));
+	if (IS_ENCRYPTED(d_inode(dentry)))
+		return __fscrypt_prepare_setattr(dentry, attr);
 	return 0;
 }