2021-01-27 21:08:32

by Orson Zhai

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

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 <[email protected]>
---
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

2021-01-27 21:35:30

by Greg Kroah-Hartman

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

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 <[email protected]>
> ---
> 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

2021-01-27 23:58:26

by Orson Zhai

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

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 <[email protected]>
> > ---
> > 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

2021-01-28 00:00:06

by Greg Kroah-Hartman

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

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 <[email protected]>
> > > ---
> > > 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