On Wed, Jan 27, 2021 at 08:50:28AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Jan 27, 2021 at 12:19:22PM +0800, Orson Zhai wrote:
> > In some circumstances, multiple __ATTR_RO attributes need to be assigned
> > with a single show function.
> >
> > Add this macro to make life easier with simple code.
> >
> > Signed-off-by: Orson Zhai <orsonzhai@xxxxxxxxx>
> > ---
> > Documentation/filesystems/sysfs.rst | 2 ++
> > include/linux/sysfs.h | 5 +++++
> > 2 files changed, 7 insertions(+)
> >
> > diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst
> > index 004d490..0e2274a 100644
> > --- a/Documentation/filesystems/sysfs.rst
> > +++ b/Documentation/filesystems/sysfs.rst
> > @@ -141,6 +141,8 @@ __ATTR_RO_MODE(name, mode):
> > fore more restrictive RO access currently
> > only use case is the EFI System Resource Table
> > (see drivers/firmware/efi/esrt.c)
> > +__ATTR_RO_SHOW(name, show):
> > + assumes default mode 0444 with specified show.
> > __ATTR_RW(name):
> > assumes default name_show, name_store and setting
> > mode to 0644.
> > diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> > index 2caa34c..c851592 100644
> > --- a/include/linux/sysfs.h
> > +++ b/include/linux/sysfs.h
> > @@ -117,6 +117,11 @@ struct attribute_group {
> > .show = _name##_show, \
> > }
> >
> > +#define __ATTR_RO_SHOW(_name, _show) { \
> > + .attr = { .name = __stringify(_name), .mode = 0444 }, \
> > + .show = _show, \
> > +}
>
> Do you have a real user for this? Using "raw" kobject attributes is
Yes, I have found at least one user in current kernel code.
Please refer to [1].
The author implemented a similar marcro __ATRR_MRO as mine, plus an
__ATRR_MWO with specified restore.
If this patch merged, I'd to replace his marcro with mine.
> rare and should not be used often, so who needs this?
Agree. But for some device drivers it might be useful without side effect.
Another example is from Android increment-fs code out there.
That driver has 3 sysfs attributes which shared with same show function
which only prints "support" to userland.
Best Regards,
Orson
>
> thanks,
>
> greg k-h
[1] https://elixir.bootlin.com/linux/v5.11-rc5/source/drivers/media/pci/ddbridge/ddbridge-core.c#L2735
