ubifs: Add skeleton for fscrypto

This is the first building block to provide file level
encryption on UBIFS.

Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/crypto.c

@@ -0,0 +1,46 @@
+#include "ubifs.h"
+
+static int ubifs_crypt_get_context(struct inode *inode, void *ctx, size_t len)
+{
+	return ubifs_xattr_get(inode, UBIFS_XATTR_NAME_ENCRYPTION_CONTEXT,
+			       ctx, len);
+}
+
+static int ubifs_crypt_set_context(struct inode *inode, const void *ctx,
+				   size_t len, void *fs_data)
+{
+	return ubifs_xattr_set(inode, UBIFS_XATTR_NAME_ENCRYPTION_CONTEXT,
+			       ctx, len, 0);
+}
+
+static bool ubifs_crypt_empty_dir(struct inode *inode)
+{
+	return ubifs_check_dir_empty(inode) == 0;
+}
+
+static unsigned int ubifs_crypt_max_namelen(struct inode *inode)
+{
+	if (S_ISLNK(inode->i_mode))
+		return UBIFS_MAX_INO_DATA;
+	else
+		return UBIFS_MAX_NLEN;
+}
+
+static int ubifs_key_prefix(struct inode *inode, u8 **key)
+{
+	static char prefix[] = "ubifs:";
+
+	*key = prefix;
+
+	return sizeof(prefix) - 1;
+}
+
+struct fscrypt_operations ubifs_crypt_operations = {
+	.flags			= FS_CFLG_INPLACE_ENCRYPTION,
+	.get_context		= ubifs_crypt_get_context,
+	.set_context		= ubifs_crypt_set_context,
+	.is_encrypted		= ubifs_crypt_is_encrypted,
+	.empty_dir		= ubifs_crypt_empty_dir,
+	.max_namelen		= ubifs_crypt_max_namelen,
+	.key_prefix		= ubifs_key_prefix,
+};