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Date: Sun, 05 Jan 2014 20:45:29 +0100
From: Antonio Quartulli <antonio@meshcoding.com>
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Subject: Re: [B.A.T.M.A.N.] [PATCH next 1/3] batctl: introduce rtnl_open()
 helper function
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To: The list for a Better Approach To Mobile Ad-hoc Networking <b.a.t.m.a.n@lists.open-mesh.org>

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On 05/01/14 15:04, Marek Lindner wrote:
> On Sunday 05 January 2014 09:59:52 Antonio Quartulli wrote:
>> @@ -528,7 +526,7 @@ static int resolve_mac_from_cache_open(int ai_fami=
ly)
>>         if (ret < 0)
>>                 goto outclose;
>> =20
>> -       ret =3D send(socknl, &nlreq, nlreq.hdr.nlmsg_len, 0);
>> +       ret =3D send(socknl, req, len, 0);
>>         if (ret < 0)
>>                 goto outclose;
>>  out:
>> @@ -538,6 +536,22 @@ outclose:
>>         return ret;
>>  }
>> =20
>> +static int resolve_mac_from_cache_open(int ai_family)
>> +{
>> +       struct {
>> +               struct nlmsghdr hdr;
>> +               struct ndmsg msg;
>> +       } nlreq;
>> +
>> +       memset(&nlreq, 0, sizeof(nlreq));
>> +       nlreq.hdr.nlmsg_len =3D NLMSG_LENGTH(sizeof(nlreq.msg));
>> +       nlreq.hdr.nlmsg_type =3D RTM_GETNEIGH;
>> +       nlreq.hdr.nlmsg_flags =3D NLM_F_REQUEST | NLM_F_DUMP;
>> +       nlreq.msg.ndm_family =3D ai_family;
>> +
>> +       return rtnl_open(&nlreq, sizeof(nlreq), NETLINK_ROUTE);
>> +}
>=20
> Is 'sizeof(nlreq)' equal to 'nlreq.hdr.nlmsg_len' ? It seems not ...

It is because the macro NLMSG_LENGTH adds NLMSG_HDRLEN to the value
passed as argument (in this case it is sizeof(nlreq.msg)) and therefore
what we store in nlreq.hdr.nlmsg_len is sizeof(nlreq) (plus some
possible alignment bytes).

I think I can make it more clear and always pass nlreq.hdr.nlmsg_len to
send().


Thanks!

v2 is coming!


Cheers,


--=20
Antonio Quartulli


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