From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] virtio-spec: split virtio-net device status filed into ro and rw byte Date: Sun, 18 Mar 2012 14:22:54 +0200 Message-ID: <20120318122252.GE29902@redhat.com> References: <20120316152026.6428.6983.stgit@jason-ThinkPad-T400> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20120316152026.6428.6983.stgit@jason-ThinkPad-T400> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jason Wang Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Fri, Mar 16, 2012 at 11:20:26PM +0800, Jason Wang wrote: > This patch splits the device status field of virtio-net into ro and rw > byte. This would simplify the implementation of both host and guest > and make the layout more clean. As VIRTIO_NET_S_ANNOUNCE is a rw bit, > it was moved to bit 8 (0x100). > > btw. looks like there's no implementation that depends on > VIRTIO_NET_S_ANNOUNCE, so the move is safe. > > Signed-off-by: Jason Wang Hmm, I know I proposed this myself, and I thought it will prevent problems if we will add more rw bits, but I missed the following race: host writes VIRTIO_NET_S_ANNOUNCE = 1, interrupt guest reads VIRTIO_NET_S_ANNOUNCE = 1 host writes VIRTIO_NET_S_SOME_NEW_FIELD = 1, interrupt guest writes VIRTIO_NET_S_ANNOUNCE = 0 VIRTIO_NET_S_SOME_NEW_FIELD is overwritten guest reads VIRTIO_NET_S_SOME_NEW_FIELD = 0 How about making the new bit write 1 to clear? If we do, we can keep it where it is currently ... > --- > virtio-0.9.4.lyx | 20 +++++++++++++++++++- > 1 files changed, 19 insertions(+), 1 deletions(-) > > diff --git a/virtio-0.9.4.lyx b/virtio-0.9.4.lyx > index 6c7bab1..ef3951c 100644 > --- a/virtio-0.9.4.lyx > +++ b/virtio-0.9.4.lyx > @@ -58,6 +58,7 @@ > \html_be_strict false > \author -608949062 "Rusty Russell,,," > \author 1531152142 "pbonzini" > +\author 2090695081 "Jason" > \end_header > > \begin_body > @@ -4012,8 +4013,19 @@ configuration > layout Two configuration fields are currently defined. > The mac address field always exists (though is only valid if VIRTIO_NET_F_MAC > is set), and the status field only exists if VIRTIO_NET_F_STATUS is set. > + > +\change_inserted 2090695081 1331907586 > + The low byte of status field is read-only, guest write to this byte would > + be ignored. > + Currently only one bit is defined for this byte: VIRTIO_NET_S_LINK_UP. > + The high byte of status field is read-writable. > + Currently only one bit is defined for this byte: VIRTIO_NET_S_ANNOUNCE. > + > +\change_deleted 2090695081 1331907489 > Two bits are currently defined for the status field: VIRTIO_NET_S_LINK_UP > and VIRTIO_NET_S_ANNOUNCE. > + > +\change_unchanged > > \begin_inset listings > inline false > @@ -4026,7 +4038,13 @@ status open > > \begin_layout Plain Layout > > -#define VIRTIO_NET_S_ANNOUNCE 2 > +#define VIRTIO_NET_S_ANNOUNCE > +\change_inserted 2090695081 1331907493 > +0x100 > +\change_deleted 2090695081 1331907491 > +2 > +\change_unchanged > + > \end_layout > > \begin_layout Plain Layout