Re: [PATCH] include: sysfs: Add macro to assign show for RO attributes

2021-01-27 Thread Greg Kroah-Hartman 
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 
> > > ---
> > >  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

Re: [PATCH] include: sysfs: Add macro to assign show for RO attributes

2021-01-27 Thread Orson Zhai 
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 
> > ---
> >  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

Re: [PATCH] include: sysfs: Add macro to assign show for RO attributes

2021-01-26 Thread Greg Kroah-Hartman 
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 
> ---
>  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
rare and should not be used often, so who needs this?

thanks,

greg k-h

[PATCH] include: sysfs: Add macro to assign show for RO attributes

2021-01-26 Thread Orson Zhai 
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 
---
 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,\
+}
+
 #define __ATTR_RO_MODE(_name, _mode) { \
.attr   = { .name = __stringify(_name), \
.mode = VERIFY_OCTAL_PERMISSIONS(_mode) },  \
-- 
2.7.4