linux-kernel - Re: [PATCH 0/7] IB/hfi1: Remove write() and use ioctl() for user access

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Message-ID: <20160419173817.GF20844@obsidianresearch.com>
Date:	Tue, 19 Apr 2016 11:38:17 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Dennis Dalessandro <dennis.dalessandro@...el.com>,
	dledford@...hat.com, linux-rdma@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, torvalds@...ux-foundation.org,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] IB/hfi1: Remove write() and use ioctl() for user
 access

On Mon, Apr 18, 2016 at 11:24:11AM -0700, Christoph Hellwig wrote:
> On Mon, Apr 18, 2016 at 11:40:47AM -0600, Jason Gunthorpe wrote:
> > I wasn't arguing this should integrate into verbs in some way, only
> > that the way to access the driver-specific uAPI of a RDMA device should
> > be through the RDMA common uAPI and not through a random char dev.
> 
> Well, it's stuff not related to our RDMA userspace API (which _is_
> Verbs, not counting for the complete crackpot abuse in usnic), but
> very device specific. 

It is weakly related, it uses the same device discovery and security
model.

> The stuff the intel driver are doing isn't pretty, but unfortunately
> not unusual either - lots of SCSI or network driver have ioctls
> like that.  Now we could argue if the ioctls should be one the
> main node (uverbs) or the a driver private chardev, or not exist
> at all and people will have to patch the driver with some vendor
> version if they really need it.  Examples for either of these
> choices exist in the tree.

Right - and the RDMA uAPI has always had an integrated driver-bypass
channel as part of the verb uAPI calls, extending that to allow for
new-driver-specific calls seems very natural.

Jason