Re: [Qemu-devel] [PATCH WIP 0/4] vhost-scsi: new device supporting the tcm_vhost Linux kernel module

[Michael S. Tsirkin]

On Fri, Feb 01, 2013 at 11:46:28AM +0800, Asias He wrote:
> On 01/31/2013 07:12 PM, Michael S. Tsirkin wrote:
> > On Wed, Jan 30, 2013 at 05:41:22PM +0100, Paolo Bonzini wrote:
> >> Ok, so here is my attempt at a vhost-scsi device.  I'm creating an
> >> entirely separate device, with the common parts of virtio-scsi and
> >> vhost-scsi (actually little more than the initialization) grouped into
> >> a VirtIOSCSICommon type.  The device is used simply like "-device
> >> vhost-scsi-pci,wwpn=WWPN", with all configuration done in configfs
> >> beforehand.
> >>
> >> As expected, using a separate device finds a snag: vhost-scsi is passing
> >> force=false to vhost_dev_init, and the BIOS does not use MSI-X so it
> >> will actually use the non-vhost implementation which is wrong.  I fixed
> >> this by passing force=true; I'm not sure what that would break, but I
> >> figured "not much" since the BIOS polls and does not rely on interrupts.
> >>
> >> That makes vhost start, but it still doesn't work for me with a 3.7.2
> >> kernel on the host.  Even Nick's patches hang the guest as soon as vhost
> >> starts, and I get the same behavior with mine.  (Of course with my
> >> patches the BIOS hangs and you never reach Linux; but try a BIOS without
> >> virtio-scsi support, and you'll see Linux hanging in the same way).
> >>
> >> Here is my configuration:
> >>
> >>   cd /sys/kernel/config/target
> >>   mkdir -p core/fileio_0/fileio
> >>   echo 'fd_dev_name=/home/pbonzini/test.img,fd_dev_size=5905580032' > 
> >> core/fileio_0/fileio/control 
> >>   echo 1 > core/fileio_0/fileio/enable
> >>   mkdir -p vhost/naa.600140554cf3a18e/tpgt_0/lun/lun_0
> >>   cd vhost/naa.600140554cf3a18e/tpgt_0
> >>   ln -sf ../../../../../core/fileio_0/fileio/ lun/lun_0/virtual_scsi_port
> >>   echo naa.60014053226f0388 > nexus
> >>
> >> Nick's patches are run with "-vhost-scsi 
> >> id=vs,tpgt=0,wwpn=naa.600140554cf3a18e
> >> -device virtio-scsi-pci,vhost-scsi=vs".  Perhaps I'm doing something wrong.
> >>
> >> Another small bug I found is an ordering problem between
> >> VHOST_SET_VRING_KICK and VHOST_SCSI_SET_ENDPOINT.  Starting the vq
> >> causes a "vhost_scsi_handle_vq endpoint not set" error in dmesg.
> >> Because of this I added the first two patches, which let me do
> >> VHOST_SCSI_SET_ENDPOINT before VHOST_SET_VRING_KICK but after setting
> >> up the vring.
> >>
> >> Unfortunately, this is not enough to fix the hang.  And anyway, it's
> >> probably simpler to avoid the two patches and remove this test from the
> >> tcm_vhost.c vhost_scsi_set/clear_endpoint functions:
> >>
> >>         mutex_lock(&vs->dev.mutex);
> >>         /* Verify that ring has been setup correctly. */
> >>         for (index = 0; index < vs->dev.nvqs; ++index) {
> >>                 /* Verify that ring has been setup correctly. */
> >>                 if (!vhost_vq_access_ok(&vs->vqs[index])) {
> >>                         mutex_unlock(&vs->dev.mutex);
> >>                         return -EFAULT;
> >>                 }
> >>         }
> >>         mutex_unlock(&vs->dev.mutex);
> > 
> > Well userspace should initialize the kick eventfd to 0,
> > it seems to init it to 1 which is why we get the error.
> > But I think the only issue is pr_err: vhost-net already
> > ignores such a kick with no backend. So let's just
> > remove it, preferably for 3.8.
> 
> With following patch, the kick before backend is set is gone.
> 
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -169,7 +169,7 @@ static int
> virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
>      int r = 0;
> 
>      if (assign) {
> -        r = event_notifier_init(notifier, false);
> +        r = event_notifier_init(notifier, 1);
> 

Hmm, not the reverse?
It's also int so should be 0 not false.


> > 
> > --->
> > tcm_vhost: fix pr_err on early kick
> > 
> > It's OK to get kick before backend is set or after
> > it is cleared, we can just ignore it.
> > 
> > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > 
> > ---
> > 
> > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> > index b20df5c..22321cf 100644
> > --- a/drivers/vhost/tcm_vhost.c
> > +++ b/drivers/vhost/tcm_vhost.c
> > @@ -575,10 +575,8 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs)
> >  
> >     /* Must use ioctl VHOST_SCSI_SET_ENDPOINT */
> >     tv_tpg = vs->vs_tpg;
> > -   if (unlikely(!tv_tpg)) {
> > -           pr_err("%s endpoint not set\n", __func__);
> > +   if (unlikely(!tv_tpg))
> >             return;
> > -   }
> >  
> >     mutex_lock(&vq->mutex);
> >     vhost_disable_notify(&vs->dev, vq);
> > 
> 
> 
> -- 
> Asias