linux-kernel - Re: [RFC PATCH] uio_hv_generic: Fix sysfs creation path for ring buffer

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Message-ID: <bb1c122e-e1bb-43fb-a71d-dde8f7aa352b@linux.microsoft.com>
Date: Fri, 14 Feb 2025 12:35:44 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 Stephen Hemminger <stephen@...workplumber.org>,
 linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...nel.org, Saurabh Sengar <ssengar@...ux.microsoft.com>
Subject: Re: [RFC PATCH] uio_hv_generic: Fix sysfs creation path for ring
 buffer

On 2/14/2025 12:21 PM, Greg Kroah-Hartman wrote:
> On Fri, Feb 14, 2025 at 12:13:51PM +0530, Naman Jain wrote:
>> On regular bootup, devices get registered to vmbus first, so when
>> uio_hv_generic driver for a particular device type is probed,
>> the device is already initialized and added, so sysfs creation in
>> uio_hv_generic probe works fine. However, when device is removed
>> and brought back, the channel rescinds and again gets registered
>> to vmbus. However this time, the uio_hv_generic driver is already
>> registered to probe for that device and in this case sysfs creation
>> is tried before the device gets initialized completely. Fix this by
>> deferring sysfs creation till device gets initialized completely.
>>
>> Problem path:
>> vmbus_device_register
>>      device_register
>>          uio_hv_generic probe
>> 		    sysfs_create_bin_file (fails here)
> 
> Ick, that's the issue, you shouldn't be manually creating sysfs files.
> Have the driver core do it for you at the proper time, which should make
> your logic much simpler, right?
> 
> Set the default attribute groups instead of manually creating this and
> see if that works out better.
> 
> thanks,
> 
> greg k-h

Thanks for reviewing Greg. I tried this approach and here are my
observations:

What I could create with ATTRIBUTE_GROUPS:
/sys/bus/vmbus/devices/eb765408-105f-49b6-b4aa-c123b64d17d4/ring

The one we have right now:
/sys/bus/vmbus/devices/eb765408-105f-49b6-b4aa-c123b64d17d4/channels/6/ring

I could not find a way to tweak attributes to create the "ring" under 
above path. I could see the variations of sys_create_* which provides a
way to pass kobj and do that, but that is something we are already
using.

Regards,
Naman