[PATCH RFC v2 10/16] btrfs: add iv generation function for fscrypt

[Sweet Tea Dorminy]

As btrfs cannot use the standard inode or logical block based encryption
for data block encryption, it must provide a IV generation function and
users must use the IV_FROM_FS policy. For filenames, we can just use the
nonce that fscrypt stores per-inode, since these encrypted datum are not
shared between inodes; later on, we will store an IV per file extent,
and return it in this function for data encryption.

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
---
 fs/btrfs/fscrypt.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/btrfs/fscrypt.c b/fs/btrfs/fscrypt.c
index 0e92acdac6d7..a11bf78c2a33 100644
--- a/fs/btrfs/fscrypt.c
+++ b/fs/btrfs/fscrypt.c
@@ -187,9 +187,21 @@ static bool btrfs_fscrypt_empty_dir(struct inode *inode)
 	return true;
 }
 
+static void btrfs_fscrypt_get_iv(u8 *iv, int ivsize, struct inode *inode,
+				 u64 lblk_num)
+{
+	/*
+	 * For encryption that doesn't involve extent data, juse use the
+	 * nonce already loaded into the iv buffer.
+	 */
+	return;
+}
+
 const struct fscrypt_operations btrfs_fscrypt_ops = {
+	.flags = FS_CFLG_ALLOW_PARTIAL,
 	.key_prefix = "btrfs:",
 	.get_context = btrfs_fscrypt_get_context,
 	.set_context = btrfs_fscrypt_set_context,
 	.empty_dir = btrfs_fscrypt_empty_dir,
+	.get_fs_defined_iv = btrfs_fscrypt_get_iv,
 };
-- 
2.35.1