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Subject: Re: [PATCH] nl80211: fix tx_control_port trace point
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     linux-wireless@vger.kernel.org
References: <20200304114952.1827-1-markus.theil@tu-ilmenau.de>
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From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Message-ID: <720231bf-8ae0-409d-039e-bc27f3d46fff@tu-ilmenau.de>
Date:   Wed, 4 Mar 2020 17:17:09 +0100
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On 3/4/20 1:36 PM, Johannes Berg wrote:
> On Wed, 2020-03-04 at 13:32 +0100, Markus Theil wrote:
>> Yes, its trace-cmd output. Without this patch, the print fmt in the
>> trace data file looks like this:
>> print fmt: "%s, netdev:%s(%d), %pM, proto: 0x%x, unencrypted: %s",
>> REC->wiphy_name, REC->name, REC->ifindex, (REC->dest),
>> (__u16)__builtin_bswap16((__u16)(( __u16)(__be16)(REC->proto))),
>> (REC->unencrypted) ? "true" : "false"
>>
>> With the patch, the builtin_bswap16 does not get placed there:
> Sure.
>
> But trace-cmd has infrastructure to handle such "function calls" in the
> output format, so it should be able to handle this pretty easily.
>
> So really it's mostly a presentation issue, and having the data in big
> endian when it's that way over the air etc. IMHO does make sense.

Sure.

Should cfg80211_rx_control_port then also adopt this behavior?
It currently does the conversion in the way I changed
cfg80211_tx_control port to.
IMHO, as long as the trace events are just printed, it is cleaner to
do the endiannes conversion already in the kernel.

TRACE_EVENT(cfg80211_rx_control_port,
...
    __entry->proto = be16_to_cpu(skb->protocol);
        __entry->unencrypted = unencrypted;
    ),
    TP_printk(NETDEV_PR_FMT ", len=%d, " MAC_PR_FMT ", proto: 0x%x,
unencrypted: %s",
          NETDEV_PR_ARG, __entry->len, MAC_PR_ARG(from),
          __entry->proto, BOOL_TO_STR(__entry->unencrypted))