Re: [PATCH 2/5] tcm_vhost: Introduce tcm_vhost_check_feature()

[Asias He <asias@redhat.com>]

On Wed, Mar 06, 2013 at 10:06:20AM +0100, Stefan Hajnoczi wrote:
> On Wed, Mar 06, 2013 at 02:16:27PM +0800, Asias He wrote:
> > This helper is useful to check if a feature is supported.
> > 
> > Signed-off-by: Asias He <asias@redhat.com>
> > ---
> >  drivers/vhost/tcm_vhost.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> > index b3e50d7..fdbf986 100644
> > --- a/drivers/vhost/tcm_vhost.c
> > +++ b/drivers/vhost/tcm_vhost.c
> > @@ -91,6 +91,20 @@ 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, u64 feature)
> > +{
> > +	u64 acked_features;
> > +	bool ret = false;
> > +
> > +	mutex_lock(&vs->dev.mutex);
> > +	acked_features = vs->dev.acked_features;
> > +	if (acked_features & 1ULL << feature)
> > +		ret = true;
> > +	mutex_unlock(&vs->dev.mutex);
> > +
> > +	return ret;
> > +}
> 
> This is like vhost_has_feature() except it acquires dev.mutex?
> 
> In any case it isn't tcm_vhost-specific and could be in vhost.c.

tcm_vhost_check_feature() is called outside the vhost worker thread. So
the dev.mutex is needed. 

Mst, what's your preference here? Add vhost_has_feature_locked() in
vhost.c or I use vhost_has_feature() in tcm_vhost_check_feature().

Thanks.
-- 
Asias