On Fri, 2 Apr 2010 15:30:10 +0800 xiaohui.xin@xxxxxxxxx wrote: > From: Xin Xiaohui <xiaohui.xin@xxxxxxxxx> > > The patch let host NIC driver to receive user space skb, > then the driver has chance to directly DMA to guest user > space buffers thru single ethX interface. > We want it to be more generic as a zero copy framework. > > Signed-off-by: Xin Xiaohui <xiaohui.xin@xxxxxxxxx> > Signed-off-by: Zhao Yu <yzhao81@xxxxxxxxx> > Sigend-off-by: Jeff Dike <jdike@xxxxxxxxxxxxxxxxxxxxxx> > --- > > We consider 2 way to utilize the user buffres, but not sure which one > is better. Please give any comments. > > One: Modify __alloc_skb() function a bit, it can only allocate a > structure of sk_buff, and the data pointer is pointing to a > user buffer which is coming from a page constructor API. > Then the shinfo of the skb is also from guest. > When packet is received from hardware, the skb->data is filled > directly by h/w. What we have done is in this way. > > Pros: We can avoid any copy here. > Cons: Guest virtio-net driver needs to allocate skb as almost > the same method with the host NIC drivers, say the size > of netdev_alloc_skb() and the same reserved space in the > head of skb. Many NIC drivers are the same with guest and > ok for this. But some lastest NIC drivers reserves special > room in skb head. To deal with it, we suggest to provide > a method in guest virtio-net driver to ask for parameter > we interest from the NIC driver when we know which device > we have bind to do zero-copy. Then we ask guest to do so. > Is that reasonable? > > Two: Modify driver to get user buffer allocated from a page constructor > API(to substitute alloc_page()), the user buffer are used as payload > buffers and filled by h/w directly when packet is received. Driver > should associate the pages with skb (skb_shinfo(skb)->frags). For > the head buffer side, let host allocates skb, and h/w fills it. > After that, the data filled in host skb header will be copied into > guest header buffer which is submitted together with the payload buffer. > > Pros: We could less care the way how guest or host allocates their > buffers. > Cons: We still need a bit copy here for the skb header. > > We are not sure which way is the better here. This is the first thing we want > to get comments from the community. We wish the modification to the network > part will be generic which not used by vhost-net backend only, but a user > application may use it as well when the zero-copy device may provides async > read/write operations later. > > > Thanks > Xiaohui How do you deal with the DoS problem of hostile user space app posting huge number of receives and never getting anything. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
