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

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Message-ID: <2025021418-cork-rinse-698a@gregkh>
Date: Fri, 14 Feb 2025 08:41:57 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Naman Jain <namjain@...ux.microsoft.com>
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 Fri, Feb 14, 2025 at 12:35:44PM +0530, Naman Jain wrote:
> 
> 
> 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

What is "channels" and "6" here?  Are they real devices or just a
directory name or something else?

> 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.

No driver should EVER be pointing to a raw kobject, that's a huge hint
that something is really wrong.  Also, if a raw kobject is in a device
path in the middle like this, it will not be seen properly from
userspace library tools :(

So again, what is creating the "channels" and "6" subdirectories?  All
of that shoudl be under full control by the uio device, right?

thanks,

greg k-h