Subject: Re: [PATCH] sysfs: add BIN_ATTR_WO() macro

From: Greg Kroah-Hartman <[email-masked]>
Date: Tue, 1 Oct 2019 20:16:01 +0200

On Tue, Oct 01, 2019 at 02:08:53PM -0400, Nayna wrote:
> Hi Greg,
> 
> 
> On 08/26/2019 11:01 AM, Greg Kroah-Hartman wrote:
> > This variant was missing from sysfs.h, I guess no one noticed it before.
> > 
> > Turns out the powerpc secure variable code can use it, so add it to the
> > tree for it, and potentially others to take advantage of, instead of
> > open-coding it.
> > 
> > Reported-by: Nayna Jain <[email-masked]>
> > Signed-off-by: Greg Kroah-Hartman <[email-masked]>
> > ---
> > 
> > I'll queue this up to my tree for 5.4-rc1, but if you want to take this
> > in your tree earlier, feel free to do so.
> > 
> >   include/linux/sysfs.h | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> > index 965236795750..5420817ed317 100644
> > --- a/include/linux/sysfs.h
> > +++ b/include/linux/sysfs.h
> > @@ -196,6 +196,12 @@ struct bin_attribute {
> >   	.size	= _size,						\
> >   }
> > +#define __BIN_ATTR_WO(_name) {						\
> > +	.attr	= { .name = __stringify(_name), .mode = 0200 },		\
> > +	.store	= _name##_store,					\
> > +	.size	= _size,						\
> > +}
> > +
> >   #define __BIN_ATTR_RW(_name, _size)					\
> >   	__BIN_ATTR(_name, 0644, _name##_read, _name##_write, _size)
> > @@ -208,6 +214,9 @@ struct bin_attribute bin_attr_##_name = __BIN_ATTR(_name, _mode, _read,	\
> >   #define BIN_ATTR_RO(_name, _size)					\
> >   struct bin_attribute bin_attr_##_name = __BIN_ATTR_RO(_name, _size)
> > +#define BIN_ATTR_WO(_name, _size)					\
> > +struct bin_attribute bin_attr_##_name = __BIN_ATTR_WO(_name, _size)
> > +
> >   #define BIN_ATTR_RW(_name, _size)					\
> >   struct bin_attribute bin_attr_##_name = __BIN_ATTR_RW(_name, _size)
> 
> I am sorry. I didn't notice it via inspection but there is a bug in this
> macro. When I actually try using it, compilation fails. Here's a likely
> patch:
> 
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index 5420817ed317..fa7ee503fb76 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -196,9 +196,9 @@ struct bin_attribute {
>         .size   = _size,                                                \
>  }
> -#define __BIN_ATTR_WO(_name) {                                         \
> +#define __BIN_ATTR_WO(_name, _size) {                                  \
>         .attr   = { .name = __stringify(_name), .mode = 0200 },         \
> -       .store  = _name##_store,                                        \
> +       .write  = _name##_write,                                        \
>         .size   = _size,                                                \
>  }
> 

Heh, good catch.  Can you send a real patch for this that I can apply to
give you the proper credit for finding and fixing this?

thanks,

greg k-h