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Date: Mon, 26 Jan 2009 21:00:06 -0700 From: Alex Williamson <alex.williamson@...com> To: Rusty Russell <rusty@...tcorp.com.au> Cc: netdev@...r.kernel.org, markmc@...hat.com, kvm@...r.kernel.org Subject: Re: [PATCH 2/5] virtio_net: Add a virtqueue for outbound control commands Hi Rusty, On Tue, 2009-01-27 at 13:52 +1030, Rusty Russell wrote: > On Saturday 17 January 2009 07:43:23 Alex Williamson wrote: > > + return status ? -EFAULT : 0; > > This is wrong. Currently this can't happen, right? But you put it in > so someone in future may want some kind of return from the commands. > In which case, they'll want to see the value. > > If we're sure they never want to see the value, then we don't need to > be synchronous at all: just spin if add_buf() fails. In my qemu series of patches it can happen if the command isn't properly defined, something bad happens, or the command is unrecognized. As I was hashing this out, I first had more errnos, but I wasn't sure how extensively to fill out the error returns, and eventually defaulted to ok/fail. Should I expand on these some? Suggestions for a reasonable small yet complete set? Should we use Linux errno values and let other OS virtio-net implementations create a switch table? I would like to keep this interface synchronous, particularly I'm wondering if there's anything we might want to do for ethtool like statistics. In that case, the backend might fill a buffer of data along with returning a status code. I could imagine other similar uses as well. > > > +struct virtio_net_ctrl_hdr { > > > + __u8 class; > > > + __u8 cmd; > > > +}; > > This would need to be __attribute__((packed)). On ARM, that struct > would be 4 bytes long. Thanks, I'll fix that. > > + > > > +typedef __u8 virtio_net_ctrl_ack; > > > + > > > +#define VIRTIO_NET_OK 0 > > > +#define VIRTIO_NET_ERR 1 > > Hmm, we define it and don't use it. And we never expect it to actually > error (did your qemu implementation ever actually return non-zero?). Yup, good point. These are mainly here to stay in sync with the qemu backend, which does make use of them. Should I remove them here, or should we make a more worthwhile set of return values? I have tried manually returning non-zero status from qemu to verify it's reflected in the response. Thanks for the comments, Alex -- Alex Williamson HP Open Source & Linux Org. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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