Function setxattr 

pub fn setxattr(
    inode: u64,
    name: &str,
    value: &[u8],
    flags: u32,
) -> Result<(), KernelError>

Set (create or replace) an extended attribute.

flags controls behaviour when the attribute already exists or not:

flags	Exists	Does not exist
0	Replace	Create
XATTR_CREATE	Error	Create
XATTR_REPLACE	Replace	Error

Returns an error if value exceeds XATTR_MAX_VALUE_SIZE or the inode already has XATTR_MAX_ATTRS_PER_INODE attributes.