__c_anonymous_* prefix policy

[Marcondiro]

Hi,
I had a look around but I haven't found any detailed documentation about how the prefix __c_anonymous_ should be used.
Specifically, I am wondering if it is mandatory for union variants.
For instance, sockaddr_can.can_addr uses the prefix for the variants:

    pub struct sockaddr_can {
        pub can_family: crate::sa_family_t,
        pub can_ifindex: c_int,
        pub can_addr: __c_anonymous_sockaddr_can_can_addr,
    }

    pub union __c_anonymous_sockaddr_can_can_addr {
        pub tp: __c_anonymous_sockaddr_can_tp,
        pub j1939: __c_anonymous_sockaddr_can_j1939,
    }
[...]

C header:

struct sockaddr_can {
	__kernel_sa_family_t can_family;
	int         can_ifindex;
	union {
		struct { canid_t rx_id, tx_id; } tp;
		struct {
			__u64 name;
			__u32 pgn;
			__u8 addr;
		} j1939;
	} can_addr;
};

While instead xsk_tx_metadata uses the prefix only for the union and not for the variants:

    pub struct xsk_tx_metadata {
        pub flags: crate::__u64,
        pub xsk_tx_metadata_union: __c_anonymous_xsk_tx_metadata_union,
    }

    pub union __c_anonymous_xsk_tx_metadata_union {
        pub request: xsk_tx_metadata_request,
        pub completion: xsk_tx_metadata_completion,
    }
[...]

struct xsk_tx_metadata {
	__u64 flags;
	union {
		struct {
			__u16 csum_start;
			__u16 csum_offset;
			__u64 launch_time;
		} request;
		struct {
			__u64 tx_timestamp;
		} completion;
	};
};

Thanks

[tgross35]

I think the first form is better here; that is, any anonymous type gets the prefix. The goal is just to guide against accidentally using these as a freestanding type when they don't exist that way in C (useful even though the prefix is ugly and I kind of hate it).

[Marcondiro]

Thanks!