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

[Pantelis Antoniou]

Hi Greg,

> On Apr 23, 2015, at 15:54 , Greg KH <greg@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx> wrote:
>>>>> 
>>>>> On Tue, Apr 7, 2015 at 2:23 PM, Pantelis Antoniou
>>>>> <pantelis.antoniou@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>>>>>> ---
>>>>>> 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.
>>>>> 
>>>> 
>>>> Itâs 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 thatâs 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 thatâs 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, Iâd 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.
> 

Thatâs 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

â Pantelis

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