On Thu, Apr 18, 2013 at 04:25:21PM +0800, Asias He wrote:
> On Thu, Apr 18, 2013 at 10:06:06AM +0300, Michael S. Tsirkin wrote:
> > On Thu, Apr 18, 2013 at 09:05:52AM +0800, Asias He wrote:
> > > This helper is useful to check if a feature is supported.
> > >
> > > Signed-off-by: Asias He <asias@xxxxxxxxxx>
> > > Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> >
> > Why do we need the locking here by the way?
> > It seems features don't change while vhost
> > is running.
>
> See:
>
> static inline int vhost_has_feature(struct vhost_dev *dev, int bit)
> {
> unsigned acked_features;
>
> /* TODO: check that we are running from vhost_worker or dev mutex is
> * held? */
> acked_features = rcu_dereference_index_check(dev->acked_features, 1);
> return acked_features & (1 << bit);
> }
>
> We are accessing it outside the vhost_worker thread.
Hmm I see, we allow changing features on the fly, and the
reason is the LOG_ALL feature.
Okay ... do we ever call this from worker
thread? Because if we do, this will deadlock.
Maybe add a comment about this.
> > > ---
> > > drivers/vhost/tcm_vhost.c | 12 ++++++++++++
> > > 1 file changed, 12 insertions(+)
> > >
> > > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> > > index 957a0b9..88ebb79 100644
> > > --- a/drivers/vhost/tcm_vhost.c
> > > +++ b/drivers/vhost/tcm_vhost.c
> > > @@ -99,6 +99,18 @@ static int iov_num_pages(struct iovec *iov)
> > > ((unsigned long)iov->iov_base & PAGE_MASK)) >> PAGE_SHIFT;
> > > }
> > >
> > > +static bool tcm_vhost_check_feature(struct vhost_scsi *vs, int feature)
> > > +{
> > > + bool ret = false;
> > > +
> > > + mutex_lock(&vs->dev.mutex);
> > > + if (vhost_has_feature(&vs->dev, feature))
> > > + ret = true;
> > > + mutex_unlock(&vs->dev.mutex);
> > > +
> > > + return ret;
> > > +}
> > > +
> > > static int tcm_vhost_check_true(struct se_portal_group *se_tpg)
> > > {
> > > return 1;
> > > --
> > > 1.8.1.4
>
> --
> Asias
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