ext4: wire up FS_IOC_GET_ENCRYPTION_NONCE

This new ioctl retrieves a file's encryption nonce, which is useful for
testing.  See the corresponding fs/crypto/ patch for more details.

Link: https://lore.kernel.org/r/20200314205052.93294-3-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/ext4/ioctl.c

@@ -1034,6 +1034,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			return -EOPNOTSUPP;
 		return fscrypt_ioctl_get_key_status(filp, (void __user *)arg);
 
+	case FS_IOC_GET_ENCRYPTION_NONCE:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_get_nonce(filp, (void __user *)arg);
+
 	case EXT4_IOC_FSGETXATTR:
 	{
 		struct fsxattr fa;
@@ -1174,6 +1179,7 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FS_IOC_REMOVE_ENCRYPTION_KEY:
 	case FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS:
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+	case FS_IOC_GET_ENCRYPTION_NONCE:
 	case EXT4_IOC_SHUTDOWN:
 	case FS_IOC_GETFSMAP:
 	case FS_IOC_ENABLE_VERITY: