linux-kernel - Re: [PATCH 5/6] ibmvscsi: Remove unsupported host config MAD and sysfs interface

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Message-ID: <20160205083413.GF27969@c203.arch.suse.de>
Date:	Fri, 5 Feb 2016 09:34:13 +0100
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Tyrel Datwyler <turtle.in.the.kernel@...il.com>
Cc:	Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
	martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
	JBottomley@...n.com, linux-kernel@...r.kernel.org, hare@...e.de,
	brking@...ux.vnet.ibm.com, nfont@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 5/6] ibmvscsi: Remove unsupported host config MAD and
 sysfs interface

On Thu, Feb 04, 2016 at 09:48:23AM -0800, Tyrel Datwyler wrote:
> On 02/04/2016 12:03 AM, Johannes Thumshirn wrote:
> > On Wed, Feb 03, 2016 at 05:28:33PM -0600, Tyrel Datwyler wrote:
> >> A VIOSRP_HOST_CONFIG_TYPE management datagram (MAD) has existed in
> >> the code for some time. From what information I've gathered from
> >> Brian King this was likely implemented on the host side in a SLES 9
> >> based VIOS, which is no longer supported anywhere. Further, it is
> >> not defined in PAPR or supported by any AIX based VIOS.
> >>
> >> Treating as bit rot and removing the sysfs interface and associated
> >> host config code accordingly.
> > 
> > Doesn't removing a sysfs interface potentially break userspace code?
> > 
> 
> In the general case yes, but I feel in this case no. First, Reading from
> this config attribute of a vscsi host adapter always returns nothing.
> Second, any userspace code using this attribute better be checking for
> the existence of config. Just a quick look for
> /sys/class/scsi_host/host*/config under other host adapters on my system
> I find that attribute doesn't exist for any of them.
> 
> If there is truly enough concern that somebody may actually be accessing
> this useless attribute from userspace then we can still strip out the
> unsupported code, but leave the attribute and return nothing directly
> from the show function.

Which is what I kinda prefer. Slowly deprecate and phase out, but don't break
userspace. You never know who is writing some obscure piece of code relaying on
some sysfs attribute.

Thanks,
	Johannes

-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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