linux-kernel - Re: [PATCH v7] Add udmabuf misc device

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Date:   Mon, 10 Sep 2018 12:53:09 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Gert Wollny <gert.wollny@...labora.com>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v7] Add udmabuf misc device

On Mon, Sep 10, 2018 at 11:18:38AM +0200, Gert Wollny wrote:
> Am Montag, den 10.09.2018, 10:37 +0200 schrieb Gerd Hoffmann:
> ... 
> 
> > > The other question is of course, why did dma_buf_export fail for me
> > > ...
> > 
> > What exactly did you try?
> 
> I ran 
> 
> qemu-system-x86_64 -enable-kvm -smp 5 -M q35 -m 8G \
>     -drive format=raw,file=ubuntu.raw,if=virtio   \
>     -net nic,model=virtio  -net user,hostfwd=tcp::2224-:22  \
>     -vga virtio

By default qemu doesn't use memfd for backing storage, you have to
explicitly configure qemu that way (see qemu commit log of the test
branch):

    qemu-system-x86_64 -m 2G
            -object memory-backend-memfd,id=ram,size=2G
            -numa node,memdev=ram"

HTH,
  Gerd