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

[Asias He]

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);


> 
> --->
> 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