netdev - Re: [PATCH-v4-RESEND 1/4] vsock: track pkt owner vsock

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Date:   Fri, 10 Mar 2017 09:48:49 +0800
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Peng Tao <bergwolf@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH-v4-RESEND 1/4] vsock: track pkt owner vsock

On Fri, Mar 03, 2017 at 09:25:54AM +0800, Peng Tao wrote:
> On Fri, Mar 3, 2017 at 5:13 AM, David Miller <davem@...emloft.net> wrote:
> > From: Peng Tao <bergwolf@...il.com>
> > Date: Wed,  1 Mar 2017 11:56:24 +0800
> >
> >> So that we can cancel a queued pkt later if necessary.
> >>
> >> Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>
> >> Signed-off-by: Peng Tao <bergwolf@...il.com>
> >> ---
> >>  include/linux/virtio_vsock.h            | 2 ++
> >>  net/vmw_vsock/virtio_transport_common.c | 7 +++++++
> >>  2 files changed, 9 insertions(+)
> >>
> >> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> >> index 9638bfe..193ad3a 100644
> >> --- a/include/linux/virtio_vsock.h
> >> +++ b/include/linux/virtio_vsock.h
> >> @@ -48,6 +48,7 @@ struct virtio_vsock_pkt {
> >>       struct virtio_vsock_hdr hdr;
> >>       struct work_struct work;
> >>       struct list_head list;
> >> +     void *cancel_token; /* only used for cancellation */
> >
> > The type here is fixed, you only store vhost_sock object pointers
> > here, so don't use "void *" please.
> It used to be "struct vhost_sock *" but no refcount is held. Stefan
> suggested to use "void *cancel_token" to make the code harder to
> misuse.
> 
> Quoting Stefan:
> "This field is just an opaque token used for cancellation rather than
> a struct vsock_sock pointer that we are allowed to dereference.  You
> could change this field to void *cancel_token to make the code harder
> to misuse."
> 
> Ref:
> https://www.mail-archive.com/netdev@vger.kernel.org/msg142550.html

Yes, the key point is that it shouldn't be used as a struct vsock_sock
since we don't hold a reference.  It's purely a token so the queued
packet can be found later for cancellation.

Stefan

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