Re: [PATCH v5 4/6] dax: check synchronous mapping is supported

[Pankaj Gupta <pagupta@redhat.com>]

> > This patch introduces 'daxdev_mapping_supported' helper
> > which checks if 'MAP_SYNC' is supported with filesystem
> > mapping. It also checks if corresponding dax_device is
> > synchronous. Virtio pmem device is asynchronous and
> > does not not support VM_SYNC.
> > 
> > Suggested-by: Jan Kara <jack@suse.cz>
> > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > ---
> >  include/linux/dax.h | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> > 
> > diff --git a/include/linux/dax.h b/include/linux/dax.h
> > index b896706a5ee9..4a2a60ffec86 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -38,6 +38,24 @@ void kill_dax(struct dax_device *dax_dev);
> >  void dax_write_cache(struct dax_device *dax_dev, bool wc);
> >  bool dax_write_cache_enabled(struct dax_device *dax_dev);
> >  bool dax_synchronous(struct dax_device *dax_dev);
> > +
> > +/*
> > + * Callers check if synchronous mapping is enabled for DAX file
> > + * and attached dax device is also synchronous.
> > + *
> > + * dax_synchronous function verifies if dax device is synchronous.
> > + * Currently, only virtio pmem device supports asynchronous device
> > + * flush.
> > + */
> 
> Thanks for the patch! I'd restructure this comment like:
> 
> /*
>  * Check if given mapping is supported by the file / underlying device.
>  */

Sure.

> > +static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
> > +				struct dax_device *dax_dev)
> > +{
> 
> 	/* Everyone supports non-sync mappings */
> > +	if (!(vma->vm_flags & VM_SYNC))
> > +		return true;
> 	/* Sync mappings are supported only for files using DAX */
> > +	if (!IS_DAX(file_inode(vma->vm_file)))
> > +		return false;
> 	/* Underlying device must support persisting through CPU instructions */
> > +	return dax_synchronous(dax_dev);
> > +}
> >  #else
> >  static inline struct dax_device *dax_get_by_host(const char *host)
> >  {
> > @@ -69,6 +87,11 @@ static inline bool dax_synchronous(struct dax_device
> > *dax_dev)
> >  {
> >  	return true;
> >  }
> > +static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
> > +				struct dax_device *dax_dev)
> > +{
> > +	return true;
> 
> This looks wrong. Shouldn't it rather be:
> 
> 	return !(vma->flags & VM_SYNC);
> 
> ?

Right. I will correct this.

Thanks,
Pankaj

> 
> 								Honza
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
>