linux-kernel - Re: [PATCH RFC] mac80211: Use IFF_ECHO to force delivery of tx

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Date:   Tue, 26 Feb 2019 12:04:09 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Julius Niedworok <julius.n@....net>, linux-wireless@...r.kernel.org
Cc:     ga58taw@...um.de, david@...hat.com, nc@....in.tum.de,
        "David S. Miller" <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Edward Cree <ecree@...arflare.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Petr Machata <petrm@...lanox.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        Li RongQing <lirongqing@...du.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] mac80211: Use IFF_ECHO to force delivery of tx_status
 frames

Hi Julius,

On 26.02.19 10:40, Julius Niedworok wrote:

> In order to force delivery of TX status frames for research and debugging
> purposes, implement the IFF_ECHO flag for ieee80211 devices. When this flag
> is set for a specific interface, IEEE80211_TX_CTL_REQ_TX_STATUS is enabled
> in all packets sent from that interface. IFF_ECHO can be set via
> /sys/class/net/<dev>/flags. The default is disabled.

(..)

> +	/*
> +	 *	Force TX status frames on ieee80211 devices.
> +	 *	Since IFF_ECHO is used by CAN devices for a different
> +	 *	purpose, we must check dev->ieee80211_ptr.
> +	 */

The reason for IFF_ECHO was, that the data frame which is sent onto the 
wire (by one application) is not visible to all the other applications 
on the same (local) host. Therefore a successful transmission on the 
wire triggers the 'echo' of the sent content into the local host.

So what are you getting back after you enabled IFF_ECHO on your mac80211 
device?

Is it just a 'status' about a sent packet, or is it the packet ('full 
content') itself?

Regards,
Oliver