linux-kernel - Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user access

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Date:	Thu, 12 May 2016 16:31:45 -0400
From:	Doug Ledford <dledford@...hat.com>
To:	Dennis Dalessandro <dennis.dalessandro@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	linux-rdma@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] IB/hfi1: Remove write() and use ioctl() for user
 access

On 05/12/2016 03:53 PM, Dennis Dalessandro wrote:
> On Thu, May 12, 2016 at 01:25:08PM -0600, Jason Gunthorpe wrote:
>> On Thu, May 12, 2016 at 03:07:38PM -0400, Dennis Dalessandro wrote:
>>> >>There is also a driver software version being exported via a sysfs
>>> >>file. This is needed so that user space applications (psm) can
>>> >>determine if it needs to do ioctl() or write().
>>> >
>>> >Why? Don't do this, just call ioctl() and if it fails then use write().
>>>
>>> Is it really that big of a deal to export a version number?
>>
>> If it isn't needed, don't add it..
> 
> For the reason I gave, I think it is needed so unless you are vehemently
> opposed to it I would prefer to leave it.

I think Jason has a point here.  In particular, if you create an ioctl
to return a driver version, it is probably safe that all future hfi1/psm
user space code can try the ioctl, in the absence of the ioctl working
assume version 0, and in the current and all future versions of the
driver, get a valid return, including potential updates to the version
number, so it's completely possible to use this as an ongoing test of
more than just "is this pre-release code or release code".


-- 
Doug Ledford <dledford@...hat.com>
              GPG KeyID: 0E572FDD



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