On Fri, Sep 10, 2021 at 07:21:01PM +0200, Krzysztof Wilczyński wrote:
> Hi Greg,
>
> [...]
> > > pci_dev_config_attr_is_visible(..., struct bin_attribute *a, ...)
> > > {
> > > a->size = PCI_CFG_SPACE_SIZE; # <-- set size in global attr
> > > ...
> > > }
> > >
> > > static struct bin_attribute *pci_dev_config_attrs[] = {
> > > &bin_attr_config, NULL,
> > > };
> > > static const struct attribute_group pci_dev_config_attr_group = {
> > > .bin_attrs = pci_dev_config_attrs,
> > > .is_bin_visible = pci_dev_config_attr_is_visible,
> > > };
> > >
> > > pci_device_add
> > > device_add
> > > device_add_attrs
> > > device_add_groups
> > > sysfs_create_groups
> > > internal_create_groups
> > > internal_create_group
> > > create_files
> > > grp->is_bin_visible()
> > > sysfs_add_file_mode_ns
> > > size = battr->size # <-- copy size from attr
> > > __kernfs_create_file(..., size, ...)
> > > kernfs_new_node
> > > __kernfs_new_node
> > >
> >
> > You can create a dynamic attribute and register that. I think some
> > drivers/busses do that today to handle this type of thing.
>
> Some static attributes users don't set size today or simply set it to 0, so
> then we report 0 bytes in userspace for each such attribute via the backing
> i-node.
>
> Would you be open to the idea of adding a .size() callback so that static
> attributes users could set size using more proper channels, or do you think
> leaving it being set to 0 is fine?
I think leaving it at 0 is fine, are userspace tools really needing to
know the size ahead of time for sysfs files? What would changing this
help out with?
thanks,
greg k-h
