Re: Fetching interface name

[Vikas <vikas.c.kumar@oracle.com>]

This will indeed help us. Thanx for the pointer.

Regards
Vikas

On 25/09/15 3:52 pm, Pablo Neira Ayuso wrote:
> Cc'ing netfilter-devel for development questions.
>
> On Fri, Sep 25, 2015 at 10:40:54AM +0530, Vikas wrote:
>> Hi,
>>
>> In the netlink infra I could see these attributes:
>>
>>   enum nfqnl_attr_type {
>> 0034     NFQA_UNSPEC,0035     NFQA_PACKET_HDR,
>> 0036     NFQA_VERDICT_HDR,       /* nfqnl_msg_verdict_hrd */
>> 0037     NFQA_MARK,          /* __u32 nfmark */
>> 0038     NFQA_TIMESTAMP,         /* nfqnl_msg_packet_timestamp */
>> 0039*NFQA_IFINDEX_INDEV*,     /* __u32 ifindex */
>> 0040*NFQA_IFINDEX_OUTDEV*,        /* __u32 ifindex */
>> 0041     NFQA_IFINDEX_PHYSINDEV,     /* __u32 ifindex */
>> 0042     NFQA_IFINDEX_PHYSOUTDEV,    /* __u32 ifindex */
>> 0043     NFQA_HWADDR,            /* nfqnl_msg_packet_hw */
>> 0044     NFQA_PAYLOAD,           /* opaque data payload */
>> 0045     NFQA_CT,            /* nf_conntrack_netlink.h */
>> 0046     NFQA_CT_INFO,           /* enum ip_conntrack_info */
>> 0047     NFQA_CAP_LEN,           /* __u32 length of captured packet */
>> 0048     NFQA_SKB_INFO,          /* __u32 skb meta information */
>> 0049     NFQA_EXP,           /* nf_conntrack_netlink.h */
>> 0050
>> 0051     __NFQA_MAX
>> 0052 };
>>
>> Currently we are doing this to get the input/putput interface index:
>>     input_interface_index = mnl_attr_get_u32(tb[NFQA_IFINDEX_INDEV]);    // where tb being a nlattr structure: struct nlattr *tb[NFQA_MAX]
>>     output_interface_index = mnl_attr_get_u32(tb[NFQA_IFINDEX_OUTDEV]);
>>
>> Is there a way(or any attribute like NFQA_IFINDEX_INDEV/OUTDEV) by
>> which we can get the input/output interface*name*?  I don't want to
>> use kernel call: if_indextoname() to map index to name, because it
>> may be time consuming.
> It should be easy to build a cache of ifindex in userspace and
> maintain it up to date. So you don't need to use if_indextoname()
> since it generates quite a lot of netlink traffic between kernel and
> userspace.
>
> You can probably contribute some example to libmnl that we can apply
> to the tree. You can use this change I made quite recently as
> reference for that code:
>
> http://git.netfilter.org/nftables/commit/?id=3ed296118a065caff5600e60d4f7ef18e137f9a0