FUSE_GETXATTR — fuse_getxattr_in (8 bytes) + name + NUL.
size = 0 is the size-probe convention: the kernel asks us how
big the value is so it can allocate a buffer; size > 0 is the
real fetch with a buffer that can hold up to that many bytes.
Summary
Types
@type t() :: %Wick.Protocol.Request.GetXattr{name: binary(), size: non_neg_integer()}