linux-kernel - Re: [RfC PATCH] Add udmabuf misc device

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Message-ID: <CAPj87rPKtuQ4SZePYDUesWY9VSSGR=1p-LO=yByY_6Q8=BfoyA@mail.gmail.com>
Date:   Fri, 6 Apr 2018 10:52:21 +0100
From:   Daniel Stone <daniel@...ishbar.org>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        qemu-devel@...gnu.org,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [RfC PATCH] Add udmabuf misc device

Hi Gerd,

On 14 March 2018 at 08:03, Gerd Hoffmann <kraxel@...hat.com> wrote:
>> Either mlock account (because it's mlocked defacto), and get_user_pages
>> won't do that for you.
>>
>> Or you write the full-blown userptr implementation, including mmu_notifier
>> support (see i915 or amdgpu), but that also requires Christian Königs
>> latest ->invalidate_mapping RFC for dma-buf (since atm exporting userptr
>> buffers is a no-go).
>
> I guess I'll look at mlock accounting for starters then.  Easier for
> now, and leaves the door open to switch to userptr later as this should
> be transparent to userspace.

Out of interest, do you have usecases for full userptr support? Maybe
another way would be to allow creation of dmabufs from memfds.

Cheers,
Daniel