[PATCH v3] dma-buf: Add a capabilities directory

[Jason Ekstrand]

On Mon, 2022-05-30 at 10:26 +0200, Greg KH wrote:
> On Mon, May 30, 2022 at 08:15:04AM +0000, Simon Ser wrote:
> > On Monday, May 30th, 2022 at 09:20, Greg KH
> > <gregkh at linuxfoundation.org> wrote:
> > 
> > > > > +static struct attribute *dma_buf_caps_attrs[] = {
> > > > > +       &dma_buf_sync_file_import_export_attr.attr,
> > > > > +       NULL,
> > > > > +};
> > > > > +
> > > > > +static const struct attribute_group dma_buf_caps_attr_group
> > > > > = {
> > > > > +       .attrs = dma_buf_caps_attrs,
> > > > > +};
> > > > 
> > > > Didn't we had macros for those? I think I have seen something
> > > > for that.
> > > 
> > > Yes, please use ATTRIBUTE_GROUPS()
> > 
> > This doesn't allow the user to set a group name, and creates an
> > unused
> > "_groups" variable, causing warnings.
> 
> Then set a group name.
> 
> But you really want to almost always be using lists of groups, which
> is
> why that macro works that way.

I think I see the confusion here.  The ATTRIBUTE_GROUPS() macro is
intended for device drivers and to be used with add_device().  However,
this is dma-buf so there is no device and no add_device() call to hook.
Unless there are other magic macros to use in this case, I think we're
stuck doing it manually.

--Jason


> > 
> > > > > +
> > > > > +static struct kobject *dma_buf_caps_kobj;
> > > > > +
> > > > > +int dma_buf_init_sysfs_capabilities(struct kset *kset)
> > > > > +{
> > > > > +       int ret;
> > > > > +
> > > > > +       dma_buf_caps_kobj = kobject_create_and_add("caps",
> > > > > &kset->kobj);
> > > > > +       if (!dma_buf_caps_kobj)
> > > > > +               return -ENOMEM;
> > > > > +
> > > > > +       ret = sysfs_create_group(dma_buf_caps_kobj,
> > > > > &dma_buf_caps_attr_group);
> > > 
> > > Why do we have "raw" kobjects here?
> > > 
> > > A group can have a name, which puts it in the subdirectory of the
> > > object
> > > it is attached to.  Please do that and do not create a new
> > > kobject.
> > 
> > I see, I'll switch to sysfs_create_group with a group name in the
> > next version.
> 
> No, do not do that, add it to the list of groups for the original
> kobject.
> 
> thanks,
> 
> greg k-h