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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>
 <5c542c4ce1b5373e8fe280913b74926f4d36e2d1.camel@sipsolutions.net>
From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Message-ID: <1073945b-ec01-7303-0bfb-92456e1ca7a5@tu-ilmenau.de>
Date:   Wed, 4 Mar 2020 13:32:31 +0100
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On 3/4/20 1:16 PM, Johannes Berg wrote:
> On Wed, 2020-03-04 at 12:49 +0100, Markus Theil wrote:
>> Endianess conversion should not happen when writing out the string,
>> instead convert proto endiannes when creating the trace point data,
>> like its already done for control port rx.
>>
>> Without this patch, trace looks like:
>> <...>-53819 [000] 12957.654875: rdev_tx_control_port: [FAILED TO PARSE]
>>   wiphy_name=phy0 name=wlan0 ifindex=3 dest=ARRAY[dc, 7b, 94, a5, bb, 3e]
>>   proto=36488 unencrypted=1
>>
>> After applying this patch:
>> wpa_supplicant-553   [001]   121.211264: rdev_tx_control_port: phy0,
>>   netdev:wlan0(3), dc:7b:94:a5:bb:3e, proto: 0x888e, unencrypted: true
> This is from trace-cmd? That just means it doesn't know about the endian
> conversion, but I don't really see any reason to change this - big
> endian is a perfectly valid format for trace points?
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:
print fmt: "%s, netdev:%s(%d), %pM, proto: 0x%x, unencrypted: %s",
REC->wiphy_name, REC->name, REC->ifindex, (REC->dest), REC->proto,
(REC->unencrypted) ? "true" : "false"

Markus
> Maybe teach trace-cmd to understand it? We already did that for
> __le16_to_cpu().
>
> johannes
>