linux-kernel - Re: New subsystem for acceleration devices

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Date:   Tue, 9 Aug 2022 01:04:15 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Dave Airlie <airlied@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
        Jiho Chu <jiho.chu@...sung.com>, Arnd Bergmann <arnd@...db.de>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: New subsystem for acceleration devices

On Tue, Aug 09, 2022 at 08:23:27AM +0200, Greg Kroah-Hartman wrote:
> Based on the number of drivers that I see submitted weekly that try to
> restrict their open call to just one user by using atomic variables or
> other tricks, I think my interpretation of this stands :)

I think they really want what Jason described most of the time.  They
just don't know about the pitfalls of dup yet.

> > This is different from the number of FDs pointing at the struct file.
> > Userpsace can open a HW state and point a lot of FDs at it, that is
> > userspace's problem. From a kernel view they all share one struct file
> > and thus one HW state.
> 
> Yes, that's fine, if that is what is happening here, I have no
> objection.

It would be great if we could actually life that into a common
layer (chardev or vfs) given just how common this, and drivers tend
to get it wrong, do it suboptimal so often.