Re: [PATCH v2 3/4] of: overlay: Add sysfs attributes

Pantelis Antoniou
2015-04-23T12:59:11Z

Hi Greg,

> On Apr 23, 2015, at 15:54 , Greg KH <greg@kroah.com> wrote:
>
> On Thu, Apr 23, 2015 at 03:39:21PM +0300, Pantelis Antoniou wrote:
>> Hi Greg,
>>
>>> On Apr 23, 2015, at 15:33 , Greg KH <greg@kroah.com> wrote:
>>>
>>> On Thu, Apr 23, 2015 at 03:00:03PM +0300, Pantelis Antoniou wrote:
>>>> Hi Rob,
>>>>
>>>>> On Apr 15, 2015, at 04:27 , Rob Herring <robherring2@gmail.com> wrote:
>>>>>
>>>>> On Tue, Apr 7, 2015 at 2:23 PM, Pantelis Antoniou
>>>>> <pantelis.antoniou@konsulko.com> wrote:
>>>>>> Implement a number of sysfs attributes for overlays.
>>>>>>
>>>>>> * A throw once master enable switch to protect against any
>>>>>> further overlay applications if the administrator desires so.
>>>>>
>>>>> This one should be a separate patch.
>>>>>
>>>>
>>>> OK.
>>>>
>>>>>> * A per overlay targets sysfs attribute listing the targets of
>>>>>> the installed overlay.
>>>>>
>>>>> What are targets? "targets lists targets" does not help me. The
>>>>> documentation doesn't help me either.
>>>>>
>>>>
>>>> It lists the targets of the overlay that has been applied. What do
>>>> you need in order to be helped? I mean what do you want listed?
>>>>
>>>>>> * A per overlay can_remove sysfs attribute that reports whether
>>>>>> the overlay can be removed or not due to another overlapping overlay.
>>>>>>
>>>>>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
>>>>>> ---
>>>>>> drivers/of/overlay.c | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>>>>>> 1 file changed, 166 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>>>>>> index f17f5ef..c54d097 100644
>>>>>> --- a/drivers/of/overlay.c
>>>>>> +++ b/drivers/of/overlay.c
>>>>>> @@ -21,6 +21,7 @@
>>>>>> #include <linux/err.h>
>>>>>> #include <linux/idr.h>
>>>>>> #include <linux/sysfs.h>
>>>>>> +#include <linux/atomic.h>
>>>>>>
>>>>>> #include "of_private.h"
>>>>>>
>>>>>> @@ -55,8 +56,12 @@ struct of_overlay {
>>>>>> struct kobject kobj;
>>>>>> };
>>>>>>
>>>>>> +/* master enable switch; once set to 0 can't be re-enabled */
>>>>>> +static atomic_t ov_enable = ATOMIC_INIT(1);
>>>>>> +
>>>>>> static int of_overlay_apply_one(struct of_overlay *ov,
>>>>>> struct device_node *target, const struct device_node *overlay);
>>>>>> +static int overlay_removal_is_ok(struct of_overlay *ov);
>>>>>>
>>>>>> static int of_overlay_apply_single_property(struct of_overlay *ov,
>>>>>> struct device_node *target, struct property *prop)
>>>>>> @@ -345,6 +350,144 @@ static struct kobj_type of_overlay_ktype = {
>>>>>>
>>>>>> static struct kset *ov_kset;
>>>>>>
>>>>>> +static ssize_t enable_read(struct file *filp, struct kobject *kobj,
>>>>>> + struct bin_attribute *bin_attr, char *buf,
>>>>>> + loff_t offset, size_t count)
>>>>>> +{
>>>>>> + char tbuf[3];
>>>>>> +
>>>>>> + if (offset < 0)
>>>>>> + return -EINVAL;
>>>>>> +
>>>>>> + if (offset >= sizeof(tbuf))
>>>>>> + return 0;
>>>>>> +
>>>>>> + if (count > sizeof(tbuf) - offset)
>>>>>> + count = sizeof(tbuf) - offset;
>>>>>> +
>>>>>> + /* fill in temp */
>>>>>> + tbuf[0] = '0' + atomic_read(&ov_enable);
>>>>>> + tbuf[1] = '\n';
>>>>>> + tbuf[2] = '\0';
>>>>>> +
>>>>>> + /* copy to buffer */
>>>>>> + memcpy(buf, tbuf + offset, count);
>>>>>> +
>>>>>> + return count;
>>>>>> +}
>>>>>> +
>>>>>> +static ssize_t enable_write(struct file *filp, struct kobject *kobj,
>>>>>> + struct bin_attribute *bin_attr, char *buf,
>>>>>> + loff_t off, size_t count)
>>>>>> +{
>>>>>> + unsigned int new_enable;
>>>>>> +
>>>>>> + if (off != 0 || (buf[0] != '0' && buf[0] != '1'))
>>>>>> + return -EINVAL;
>>>>>> +
>>>>>> + new_enable = (unsigned int)(buf[0] - '0');
>>>>>> + if (new_enable > 1)
>>>>>> + return -EINVAL;
>>>>>> +
>>>>>> + /* NOP for same value */
>>>>>> + if (new_enable == atomic_read(&ov_enable))
>>>>>> + return count;
>>>>>> +
>>>>>> + /* if we've disabled it, no going back */
>>>>>> + if (atomic_read(&ov_enable) == 0)
>>>>>> + return -EPERM;
>>>>>> +
>>>>>> + atomic_set(&ov_enable, new_enable);
>>>>>> + return count;
>>>>>> +}
>>>>>> +
>>>>>> +/* just a single char + '\n' + '\0' */
>>>>>> +static BIN_ATTR_RW(enable, 3);
>>>>>
>>>>> Why are you using bin attribute? You are complicating the
>>>>> implementation needlessly.
>>>>>
>>>>
>>>> It’s the same reason that the device tree core is using it.
>>>
>>> It is doing that for "raw" device tree files, not individual attributes,
>>> right?
>>>
>>
>> Each property of a device tree is a binary attribute.
>
> Because they export binary data, right? I don't have access to a
> machine that uses device tree at the moment to check this...
>
> Any specific file/function you are referring to?
>

Yes, they export binary data. It works because the device tree nodes
are raw kobjs.

>>>> Believe it or not, this is the simplest way to do it.
>>>> If you take a look at the sysfs attribute implementation, the binary
>>>> implementation is the one that’s using the least amount of code.
>>>
>>> Then something is really wrong here.
>>>
>>>> To use a non-binary method we have to register per ktype sysfs_ops
>>>> and duplicate the way the non-binary attribute works.
>>>
>>> really? Again, something must be wrong.
>>>
>>>> For the gory details look at sysfs_add_file_mode_ns() in fs/sysfs/file.c
>>>>
>>>> I can add the sysfs_ops but that’s going to be more complicated not less.
>>>
>>
>> Please take a look in linux/sysfs.h.
>> The non-binary sysfs accessors are all using some kind of other kobj;
>> for instance DEVICE_ATTR is using a device_attribute, etc.
>>
>> For the overlay case, I’d have to create a of_overlay_attribute and work from
>> there.
>
> Yes, that is what you should be doing here as well.
>
> That's just the model we have to work with, the uses of "raw" kobjects
> are very limited, so it does take a bit more wrapper code to use them,
> sorry.
>

That’s fine, I can work with this. I was trying to avoid creating overlay
attributes but...

> You need access to the kobject anyway, which is why you need to provide
> a type of attribute function, so that you get the right kobject.
>
> Or just use an attribute group, would that be simpler? If you have more
> than one sysfs file, that's usually the best way to do things.
>

Attribute groups might work, but I have some more work to do to get them to
work.

Thanks for answering definitively this.

> thanks,
>
> greg k-h

Regards

— Pantelis