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[RTNETLINK]: Add nested compat attribute

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Add a nested compat attribute type that can be used to convert
attributes that contain a structure to nested attributes in a
backwards compatible way.

The attribute looks like this:

struct {
        [ compat contents ]
        struct rtattr {
                .rta_len        = total size,
                .rta_type       = type,
        } rta;
        struct old_structure struct;

        [ nested top-level attribute ]
        struct rtattr {
                .rta_len        = nest size,
                .rta_type       = type,
        } nest_attr;

        [ optional 0 .. n nested attributes ]
        struct rtattr {
                .rta_len        = private attribute len,
                .rta_type       = private attribute typ,
        } nested_attr;
        struct nested_data data;
};

Since both userspace and kernel deal correctly with attributes that are
larger than expected old versions will just parse the compat part and
ignore the rest.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Patrick McHardy 2007-06-25 14:30:16 -07:00 • committed by David S. Miller
parent 1092cb2197
commit afdc3238ec
2 changed files with 30 additions and 0 deletions
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14
include/linux/rtnetlink.h
View file

@ -570,6 +570,8 @@ static __inline__ int rtattr_strcmp(const struct rtattr *rta, const char *str)
}
extern int rtattr_parse(struct rtattr *tb[], int maxattr, struct rtattr *rta, int len);
extern int rtattr_parse_nested_compat(struct rtattr *tb[], int maxattr,
struct rtattr *rta, void **data, int len);
#define rtattr_parse_nested(tb, max, rta) \
rtattr_parse((tb), (max), RTA_DATA((rta)), RTA_PAYLOAD((rta)))
@ -638,6 +640,18 @@ extern void __rta_fill(struct sk_buff *skb, int attrtype, int attrlen, const voi
({ (start)->rta_len = skb_tail_pointer(skb) - (unsigned char *)(start); \
(skb)->len; })
#define RTA_NEST_COMPAT(skb, type, attrlen, data) \
({ struct rtattr *__start = (struct rtattr *)skb_tail_pointer(skb); \
RTA_PUT(skb, type, attrlen, data); \
RTA_NEST(skb, type); \
__start; })
#define RTA_NEST_COMPAT_END(skb, start) \
({ struct rtattr *__nest = (void *)(start) + NLMSG_ALIGN((start)->rta_len); \
(start)->rta_len = skb_tail_pointer(skb) - (unsigned char *)(start); \
RTA_NEST_END(skb, __nest); \
(skb)->len; })
#define RTA_NEST_CANCEL(skb, start) \
({ if (start) \
skb_trim(skb, (unsigned char *) (start) - (skb)->data); \