Re: [Qemu-devel] [RFC v2 1/2] virtio: add pmem driver

> > > + int err; > > > + > > > + sg_init_one(&sg, buf, sizeof(buf)); > > > + > > > + err = virtqueue_add_outbuf(vpmem->req_vq, &sg, 1, buf, GFP_KERNEL); > > > + > > > + if (err) { > > > + dev_err(&vdev->dev, "failed to send command to virtio pmem > > > device\n"); > > > + return; > > > + } > > > + > > > + virtqueue_kick(vpmem->req_vq); > > > > Is any locking necessary? Two CPUs must not invoke virtio_pmem_flush() > > at the same time. Not sure if anything guarantees this, maybe you're > > relying on libnvdimm but I haven't checked. > > I thought about it to some extent, and wanted to go ahead with simple > version first: > > - I think file 'inode -> locking' sill is there for request on single file. > - For multiple files, our aim is to just flush the backend block image. > - Even there is collision for virt queue read/write entry it should just > trigger a Qemu fsync. > We just want most recent flush to assure guest writes are synced > properly. > > Important point here: We are doing entire block fsync for guest virtual > disk. I don't understand your answer. Is locking necessary or not?

From the virtqueue_add_outbuf() documentation: * Caller must ensure we don't call this with other virtqueue operations * at the same time (except where noted).