netdev - Re: [PATCH net-next] mctp i2c: notify user space on TX failure

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Message-ID: <20241115-scrupulous-mantis-of-purring-1c41fe-mkl@pengutronix.de>
Date: Fri, 15 Nov 2024 09:30:54 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jeremy Kerr <jk@...econstruct.com.au>, 
	Jian Zhang <zhangjian.3032@...edance.com>, netdev@...r.kernel.org, openbmc@...ts.ozlabs.org, 
	Matt Johnston <matt@...econstruct.com.au>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] mctp i2c: notify user space on TX failure

On 14.11.2024 07:02:35, Jakub Kicinski wrote:
> On Thu, 14 Nov 2024 14:48:57 +0800 Jeremy Kerr wrote:
> > > routing isn't really my forte, TBH, what eats the error so that it
> > > doesn't come out of mctp_local_output() ? Do you use qdiscs on top
> > > of the MCTP devices?  
> > 
> > There are no qdiscs involved at this stage, as we need to preserve
> > packet ordering in most cases. The route output functions will end up
> > in a dev_queue_xmit, so any tx error would have been decoupled from the
> > route output at that stage.
> 
> Ah, it's the driver eating the errors, it puts the packet on a local
> queue and returns OK no matter what. The I2C transfer happens from 
> a thread.
> 
> I wonder if there is precedent, let's ask CAN experts.
> 
> Mark, MCTP would like to report errors from the drivers all the way 
> to the socket. Do CAN drivers do something along these lines?

On CAN_RAW we send fixed size messages (struct can_frame) and there is a
bit left to mark a can_frame as an error frame. This basically means we
send the error notification inline.

What about using sock_queue_err_skb()? We do this in CAN_J1939.

regards,
Marc

-- 
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