linux-kernel - Re: [PATCH 3/3] nvmem: core: use is_bin

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Date:   Wed, 25 Mar 2020 08:36:56 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] nvmem: core: use is_bin_visible for permissions

On Tue, Mar 24, 2020 at 11:05:07PM +0000, Nicholas Johnson wrote:
> On Tue, Mar 24, 2020 at 05:16:00PM +0000, Srinivas Kandagatla wrote:
> > By using is_bin_visible callback to set permissions will remove a large list
> > of attribute groups. These group permissions can be dynamically derived in
> > the callback.
> > 
> > Suggested-by: Greg KH <gregkh@...uxfoundation.org>
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> > ---
> >  drivers/nvmem/nvmem-sysfs.c | 74 +++++++++----------------------------
> >  1 file changed, 18 insertions(+), 56 deletions(-)
> > 
> > diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c
> > index 8759c4470012..1ff1801048f6 100644
> > --- a/drivers/nvmem/nvmem-sysfs.c
> > +++ b/drivers/nvmem/nvmem-sysfs.c
> > @@ -103,6 +103,17 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
> >  
> >  	return count;
> >  }
> > +static umode_t nvmem_bin_attr_is_visible(struct kobject *kobj,
> > +					 struct bin_attribute *attr, int i)
> > +{
> > +	struct device *dev = container_of(kobj, struct device, kobj);
> > +	struct nvmem_device *nvmem = to_nvmem_device(dev);
> > +
> > +	if (nvmem->root_only)
> > +		return nvmem->read_only ? 0400 : 0600;
> > +
> > +	return nvmem->read_only ? 0444 : 0644;
> > +}
> Looks like I did a pretty good job as I arrived at a similar result 
> independently. Even added root_only to nvmem_device. You beat me to it. 
> :)
> 
> >  const struct attribute_group **nvmem_sysfs_get_groups(
> >  					struct nvmem_device *nvmem,
> >  					const struct nvmem_config *config)
> >  {
> > -	if (config->root_only)
> > -		return nvmem->read_only ?
> > -			nvmem_ro_root_dev_groups :
> > -			nvmem_rw_root_dev_groups;
> > -
> > -	return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups;
> > +	return nvmem_dev_groups;
> >  }
> I was wondering if we can export nvmem_dev_group instead of this 
> nvmem_sysfs_get_groups() to fetch it.
> 
> Also, we need some logic in nvmem_register() to abort if bad combination 
> is given (i.e. root_only set but no reg_read), as returning 0 in 
> is_bin_visible callback does not abort. I can do that in my patch if you 
> want.

Returning 0 will cause the file to not be created at all, which is
probably what you want, right?

thanks,

greg k-h