From: Nicolas Dichtel <nicolas.dichtel@6wind•com>
To: David Laight <David.Laight@ACULAB•COM>
Cc: bhutchings@solarflare•com, tgraf@suug•ch, netdev@vger•kernel.org,
davem@davemloft•net
Subject: Re: [PATCH v2] netlink: align attributes on 64-bits
Date: Mon, 17 Dec 2012 18:35:24 +0100 [thread overview]
Message-ID: <50CF57DC.5050804@6wind.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B70F1@saturn3.aculab.com>
Le 17/12/2012 18:06, David Laight a écrit :
>> int nla_put(struct sk_buff *skb, int attrtype, int attrlen, const void *data)
>> {
>> - if (unlikely(skb_tailroom(skb) < nla_total_size(attrlen)))
>> + int align = IS_ALIGNED((unsigned long)skb_tail_pointer(skb), 8) ? 0 : 4;
>
> I've just realised where you are adding this!
> You only want to add pad if the attribute is a single 64bit item,
> not whenever the destination is misaligned.
As said in the commit log, I want to align all attributes. An attribute can be
like this:
struct foo {
__u32 bar1;
__u32 bar2;
__u64 bar3;
}
nla_put() don't know what is contained in the attribute.
>
> Eg what happens if you add a 4-byte item after an 8 byte one.
>
> Are there are attributes that consist of a pair of 4 byte values?
>
> ...
>> + if (align) {
>> + /* Goal is to add an attribute with size 4. We know that
>> + * NLA_HDRLEN is 4, hence payload is 0.
>> + */
>> + __nla_reserve(skb, 0, 0);
>
> One of those zeros should be 'align - 4', then the comment
> can be more descriptive.
I thought if you were to research why we use 0, you would know that the first 0
is the type and the second is the payload size...
next prev parent reply other threads:[~2012-12-17 17:35 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-04 11:13 [PATCH net-next 0/7] Allow to monitor multicast cache event via rtnetlink Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 1/7] netconf: advertise mc_forwarding status Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 2/7] ip6mr: use nla_nest_* helpers Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 3/7] ipmr/ip6mr: advertise mfc stats via rtnetlink Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 4/7] ipmr/ip6mr: report origin of mfc entry into rtnl msg Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 5/7] ipmr/ip6mr: allow to get unresolved cache via netlink Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 6/7] ipmr: advertise new mfc entries via rtnl Nicolas Dichtel
2012-12-04 11:13 ` [PATCH net-next 7/7] ip6mr: " Nicolas Dichtel
2012-12-04 18:09 ` [PATCH net-next 0/7] Allow to monitor multicast cache event via rtnetlink David Miller
2012-12-04 20:02 ` Nicolas Dichtel
2012-12-05 11:02 ` Nicolas Dichtel
2012-12-05 11:41 ` David Laight
2012-12-05 17:54 ` David Miller
2012-12-06 8:43 ` Nicolas Dichtel
2012-12-06 17:49 ` Thomas Graf
2012-12-06 21:49 ` Nicolas Dichtel
2012-12-07 10:38 ` David Laight
2012-12-07 10:58 ` Thomas Graf
2012-12-11 15:03 ` Nicolas Dichtel
2012-12-11 18:40 ` Thomas Graf
2012-12-12 17:30 ` Nicolas Dichtel
2012-12-14 13:16 ` [PATCH] netlink: align attributes on 64-bits Nicolas Dichtel
2012-12-14 15:49 ` Ben Hutchings
2012-12-14 16:04 ` Nicolas Dichtel
2012-12-17 16:49 ` [PATCH v2] " Nicolas Dichtel
2012-12-17 17:06 ` David Laight
2012-12-17 17:35 ` Nicolas Dichtel [this message]
2012-12-18 9:19 ` David Laight
2012-12-18 10:18 ` Nicolas Dichtel
2012-12-18 12:57 ` Thomas Graf
2012-12-18 16:23 ` Nicolas Dichtel
2012-12-18 16:50 ` David Laight
2012-12-18 17:11 ` Thomas Graf
2012-12-19 9:17 ` David Laight
2012-12-19 17:20 ` Thomas Graf
2012-12-20 9:37 ` David Laight
2012-12-20 9:40 ` David Laight
2012-12-18 17:08 ` Thomas Graf
2012-12-18 22:07 ` Nicolas Dichtel
2012-12-19 11:22 ` Nicolas Dichtel
2012-12-19 17:09 ` Thomas Graf
2012-12-19 18:07 ` Nicolas Dichtel
2012-12-17 9:59 ` [PATCH] " David Laight
2012-12-17 16:53 ` Nicolas Dichtel
2012-12-05 17:53 ` [PATCH net-next 0/7] Allow to monitor multicast cache event via rtnetlink David Miller
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