On Wed, Jan 27, 2021 at 08:51:26PM +0800, Orson Zhai wrote:
> 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.
Ick, no, that should be using DEVICE_ATTR_RO() as it is a struct device
attribute, not a "raw" kobject attribute. So that code should be fixed
up anyway, no need for this macro :)
>
> 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.
Drivers should NOT be ever using __ATTR* macros. That is not what they
are there for.
> 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.
I can't take patches for out-of-tree code, sorry, you know this :)
thanks,
greg k-h
