Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <a15716609a2c88e1591581539fd637f7385571e4.camel@sipsolutions.net>
Subject: Re: [PATCH v2] cfg80211: add local BSS receive time to survey
 information
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Marcel Holtmann <marcel@holtmann.org>
Cc:     Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
Date:   Wed, 28 Aug 2019 21:59:01 +0200
In-Reply-To: <F29BC537-AED5-4BFA-915F-ED8E749124FC@holtmann.org>
References: <20190828102042.58016-1-nbd@nbd.name>
         <9189B2C1-6E5B-4457-9354-A010F946EE33@holtmann.org>
         <18c4232675c7b4f13fbfe9e5d8e9364a0908f316.camel@sipsolutions.net>
         <F29BC537-AED5-4BFA-915F-ED8E749124FC@holtmann.org>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

Hi Marcel,

> > No, as usual, that would break ABI. PAD is a regular attribute, just
> > empty and ignored for aligning 64-bit values.
> 
> then I do not grok on how the nla_put_u64_64bit works, but that is
> fine.
> 
> I assumed these are similar to the NL80211_SURVEY_INFO_MAX which we
> also always move, but also not expected to be part of the API as a
> fixed value.

No no, the _MAX is just the token we use for knowing what we want as the
maximum when parsing etc.

The _PAD is actually a real attribute, basically nla_put_u64_64bit()
will do "nla_put_flag(_PAD)" if and only if "offset % 8 == 0", in order
to actually 64-bit align the 64-bit value in the following attribute.

(Note that offset % 8 can only be 0 or 4, due to the way netlink
attributes work.)

johannes