__struct_group
浏览IPv6代码时候，看到这样一个新玩法，__struct_group
1 | 118 struct ipv6hdr { |
###用法
再看一下用法：
922 /* copy IPv6 saddr & daddr to flow_keys, possibly using 64bit load/store
923 * Equivalent to : flow->v6addrs.src = iph->saddr;
924 * flow->v6addrs.dst = iph->daddr;
925 */
926 static inline void iph_to_flow_copy_v6addrs(struct flow_keys *flow,
927 const struct ipv6hdr *iph)
928 {
...
932 memcpy(&flow->addrs.v6addrs, &iph->addrs, sizeof(flow->addrs.v6addrs));
...
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###
11 /**
12 * __struct_group() - Create a mirrored named and anonyomous struct
13 *
14 * @TAG: The tag name for the named sub-struct (usually empty)
15 * @NAME: The identifier name of the mirrored sub-struct
16 * @ATTRS: Any struct attributes (usually empty)
17 * @MEMBERS: The member declarations for the mirrored structs
18 *
19 * Used to create an anonymous union of two structs with identical layout
20 * and size: one anonymous and one named. The former's members can be used
21 * normally without sub-struct naming, and the latter can be used to
22 * reason about the start, end, and size of the group of struct members.
23 * The named struct can also be explicitly tagged for layer reuse, as well
24 * as both having struct attributes appended.
25 */
26 #define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \
27 union { \
28 struct { MEMBERS } ATTRS; \
29 struct TAG { MEMBERS } ATTRS NAME; \
30 } ATTRS
```