Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <59e18374-0941-1298-4119-366452375404@suse.com>
Date:   Wed, 2 Feb 2022 10:14:24 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH net-next v1 1/1] usbnet: add devlink support
Content-Language: en-US
To:     Oleksij Rempel <o.rempel@pengutronix.de>,
        Greg KH <gregkh@linuxfoundation.org>
CC:     Oliver Neukum <oneukum@suse.com>, netdev@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@pengutronix.de, Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
References: <20220127110742.922752-1-o.rempel@pengutronix.de>
 <YfJ+ceEzvzMM1JsW@kroah.com> <20220127123152.GF9150@pengutronix.de>
 <YfKcqcq4Ii1qu2+8@kroah.com> <YfPPpkGjL2vcv4oH@pengutronix.de>
From:   Oliver Neukum <oneukum@suse.com>
In-Reply-To: <YfPPpkGjL2vcv4oH@pengutronix.de>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?p80v6NX8vrDjFwNapdvUM1AuXW2XTBhrW9ahx3bN7uFJ7I8rU56nKnk2TjAE?=
 =?us-ascii?Q?+SAl6GV7+uoN90zw7Xm12WnXc6T6R8PdRTYiRGV+V7riCOqIrlmnPFlSkY+4?=
 =?us-ascii?Q?wXiichN1K7CBkT7PMk1VGR7PV6UimnrEsDrlYgKA6iNdKmASLqGQrP968iTW?=
 =?us-ascii?Q?wGglAXtydxprZTW/JhH87CchkIayXmZkWiUYd6a3lFsTbbhaWX+PkQhz8DGG?=
 =?us-ascii?Q?vrK9QYtFR5Ld08QfYNy5AxzQjhIXUDy7oi2aeIW/fms94cSkc6jVY8DrX6Mp?=
 =?us-ascii?Q?jp34k2fk5nHTUBOS/YndXvangz9DQx/GMnPiEBFmtifnOFzlzM46RsaGgqsK?=
 =?us-ascii?Q?pw17/XbKucoQhif0dnWXEuVU/E9I0OZl1hMTbJkvCK5J28x0W3cKX/3RrIy4?=
 =?us-ascii?Q?qNxyJhpmOgbSpbdKmscElZ5PbjU+O1sVSPvIgRdHzt2usYx/aqoocNTevXwG?=
 =?us-ascii?Q?wwQd2aoPS7PTXPx7+kpLhga0HJ1IhzLO69ofO+QSVZWasr4CTM5UJeNTBVcr?=
 =?us-ascii?Q?CBXQLkDgS1WUsQE/FSGM30M2lgh2tCLtWhUBYexrO4YGYIGPnpWVmGZakBHu?=
 =?us-ascii?Q?mJwPPQIPAwmDxn+er7NBpx1JOSjbnPPrVYDVgKkJ4RbkqPabce7cBrBt/cuY?=
 =?us-ascii?Q?Dda554xGVjqPtOKNW1Zw6o4TeRvGv8YcbNzI1AYTnArWCnzTSkZZd6CQje1w?=
 =?us-ascii?Q?zm/N5h+CSdKNGZ/LawEedZSJCCkKRQsTRNyvxNp6hE6KcJHJV0qMfw/3/D0B?=
 =?us-ascii?Q?ltP0op4MOeVJsFfN32EbFGQIFAlt3GmLeXDuAe1aitICFCKk7sLIh9LncODe?=
 =?us-ascii?Q?4TMKVMtScmVe//WEsdkbq04ESy4pZ8+VCEM/08SMZxdnSx3wGJClzGjEAbY2?=
 =?us-ascii?Q?vsf1axBXlI/wA6yu2RfLU5ka5P6J3vh6deg7cg5Tbu02F14ykYjRdjtYzO8r?=
 =?us-ascii?Q?dPXChwIm9l99g+HJgLawxvWhIu9nnPu5MkkZZ6nL4lVbQUCqQV+OGyE0wxQd?=
 =?us-ascii?Q?7MbaSNXgkkfNeXH1V5a9jKZ4CLIFlkJKBBP4WUuaxC9cxXWVKOlFNRrlunF4?=
 =?us-ascii?Q?Tg2a1GHaETJLTtB4xyyKnF2WiVykTYcHHwAk09wokCqMMGvJCKjJAU7ZarVP?=
 =?us-ascii?Q?O3EKlQwddkhVMpJJapHKoDjwFYae+JcqDDxtIRwALBYFtmmtsWU05CDnXRck?=
 =?us-ascii?Q?VOT3gZVd5vOwhRNhGK+fuvaAVqzPYpZ/PFRB5jVRtDAR+O5SIYuV7CAh0Rfa?=
 =?us-ascii?Q?vxTDrqbBss8QnCZ2lCMOXoA9r18bKnsERjuxqMWn80MqHc0QbDpGo6kCLPrv?=
 =?us-ascii?Q?OO12t7JAY/72bF0QmaTdUl7Hq8IiP6Yh/yLhTuc7miWt2RwBpKZHOanJuegB?=
 =?us-ascii?Q?TeDC74d5m5OOpWJZDjbVnsNrMtdpOtLWh4OBNAuQ6nmpkgKDLBYvviIKjDXB?=
 =?us-ascii?Q?LpXW0O/+yuvy1fV8dnqUf8OHUV8o63zi3Iuzd4frj5mNiUn5QHIRzJnJicPi?=
 =?us-ascii?Q?Sh7tAggqgEFvS5bI+qN9Z8vUu09xmu6Yzp63e6BbvI8z3QuHQMv84joMwLe9?=
 =?us-ascii?Q?+iGWwPtWftvXXjIpUKUblkj7VQSkvZ2UdQWRiq73b6UHQvJ2zhRpQBZQ+y9G?=
 =?us-ascii?Q?MzD5sdguURNnP1Euw+nn0r5IexRiT3mLn2sILvVGRGz0UobV/LGoXEescQ33?=
 =?us-ascii?Q?e06ZDMU8b8kkfx6Z3TU8gYWXQIs=3D?=
X-OriginatorOrg: suse.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 8d59b0fb-f3f2-4a50-699f-08d9e62c6901
X-MS-Exchange-CrossTenant-AuthSource: DB7PR04MB5050.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Feb 2022 09:14:26.5535
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: Mocsg7xctJB0xnP3WUKVccdHLZCyndul8aNwLcWcgSUTZqezRhl0gUUvqONnx/MfY5laV0L+ypDhVIkcftIyog==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PR3PR04MB7227
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 28.01.22 12:12, Oleksij Rempel wrote:
> The user space should get an event in case there is a problem with the
> USB transfers, i.e. the URB status is !=3D 0.
That would need filtering for unlinks, but that is a detail
> The use space then can decide if the USB device needs to be reset, power
> cycled and so on.

This is highly problematic. Not necessarily impossible but problematic.

Executing URBs is part of the

* device removal and addition IO paths
* block IO path
* SCSI error handling
* PM transition IO paths

While we can send messages to user space, we cannot allocate a lot
of memory and we cannot wait for responses.

> What about calling a to-be-written devlink function that reports the USB
> status if the URB status is not 0:
>
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index d0f45600b669..a90134854f32 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1648,6 +1648,8 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
>  	usb_unanchor_urb(urb);
>  	if (likely(status =3D=3D 0))
>  		usb_led_activity(USB_LED_EVENT_HOST);
> +	else
> +		devlink_report_usb_status(urb, status);
> =20
> =20
It seems to me that you are approaching this issue on too low
a level. Drivers generally do at least rudimentary error handling
or rather detection.

This would be easy to use if you gave them a nice API. Something
like:

devlink_report_urb_error(usb_interface * intf, int reason, bool handling);

Maybe also report resets and hub events from the hub driver and
I think you'd get what you need. You need to be aware of a need for
some kind of limiting logic for disconnects.

The change over from logging something not very helpful to
properly reporting is easy.

=C2=A0=C2=A0=C2=A0 Regards
=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 Oliver