On Fri, Dec 14, 2018 at 09:56:41AM +0800, Yongji Xie wrote: > On Thu, 13 Dec 2018 at 22:45, Michael S. Tsirkin <m...@redhat.com> wrote: > > > > On Thu, Dec 06, 2018 at 02:35:46PM +0800, elohi...@gmail.com wrote: > > > From: Xie Yongji <xieyon...@baidu.com> > > > > > > This patchset is aimed at supporting qemu to reconnect > > > vhost-user-blk backend after vhost-user-blk backend crash or > > > restart. > > > > > > The patch 1 tries to implenment the sync connection for > > > "reconnect socket". > > > > > > The patch 2 introduces a new message VHOST_USER_SET_VRING_INFLIGHT > > > to support offering shared memory to backend to record > > > its inflight I/O. > > > > > > The patch 3,4 are the corresponding libvhost-user patches of > > > patch 2. Make libvhost-user support VHOST_USER_SET_VRING_INFLIGHT. > > > > > > The patch 5 supports vhost-user-blk to reconnect backend when > > > connection closed. > > > > > > The patch 6 tells qemu that we support reconnecting now. > > > > > > To use it, we could start qemu with: > > > > > > qemu-system-x86_64 \ > > > -chardev socket,id=char0,path=/path/vhost.socket,reconnect=1,wait > > > \ > > > -device vhost-user-blk-pci,chardev=char0 \ > > > > > > and start vhost-user-blk backend with: > > > > > > vhost-user-blk -b /path/file -s /path/vhost.socket > > > > > > Then we can restart vhost-user-blk at any time during VM running. > > > > > > Xie Yongji (6): > > > char-socket: Enable "wait" option for client mode > > > vhost-user: Add shared memory to record inflight I/O > > > libvhost-user: Introduce vu_queue_map_desc() > > > libvhost-user: Support recording inflight I/O in shared memory > > > vhost-user-blk: Add support for reconnecting backend > > > contrib/vhost-user-blk: enable inflight I/O recording > > > > What is missing in all this is documentation. > > Specifically docs/interop/vhost-user.txt. > > > > At a high level the design is IMO a good one. > > > > However I would prefer reading the protocol first before > > the code. > > > > So here's what I managed to figure out, and it matches > > how I imagined it would work when I was still > > thinking about out of order for net: > > > > - backend allocates memory to keep its stuff around > > - sends it to qemu so it can maintain it > > - gets it back on reconnect > > > > format and size etc are all up to the backend, > > a good implementation would probably implement some > > kind of versioning. > > > > Is this what this implements? > > > > Definitely, yes. And the comments looks good to me. Qemu get size and > version from backend, then allocate memory and send it back with > version. Backend knows how to use the memory according to the version. > If we do that, should we allocate the memory per device rather than > per virtqueue? > > Thanks, > Yongji
It's up to you. Maybe both. -- MST
