On Fri, Sep 01, 2023 at 02:13:23AM -0700, Zev Weiss wrote:
> Adding Greg re: sysfs ABI design...
>
> On Thu, Aug 31, 2023 at 05:14:10AM PDT, Naresh Solanki wrote:
> > Adds sysfs-driver-regulator-output
> >
> > Signed-off-by: Naresh Solanki <[email protected]>
> > ---
> > .../ABI/testing/sysfs-driver-regulator-output | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> > create mode 100644 Documentation/ABI/testing/sysfs-driver-regulator-output
> >
> > diff --git a/Documentation/ABI/testing/sysfs-driver-regulator-output b/Documentation/ABI/testing/sysfs-driver-regulator-output
> > new file mode 100644
> > index 000000000000..f9b0a8f810fa
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-driver-regulator-output
> > @@ -0,0 +1,11 @@
> > +What: /sys/bus/platform/drivers/regulator-output/*/events
> > +Date: August 2023
> > +Description: Provided regulator events.
> > +
> > + Read provides various events the regulator associated with the
> > + driver has encountered. All REGULATOR_EVENT_* are
> > + defined in include/uapi/linux/regulator.h
> > +
> > + e.g.
> > + cat /sys/bus/platform/drivers/regulator-output/ssb_rssd32/events
> > + 0x0
>
> If we really are going to proceed with a "read with side-effects"
> (clear-on-read) design, that should absolutely be loudly and clearly
> documented, since it's very different from how sysfs files typically work
> and hence a somewhat glaring principle-of-least-surprise violation. Also,
> since from the code it looks like it's intended to be used via poll(2), that
> should be described here as well.
Poll? Ick, but that can happen.
But yes, reading a sysfs should almost never cause a side affect at all.
But what do you mean by "clear events?" sysfs is only "one value per
file", so you are only returning a single event, right? It can't be a
list of events, sorry, that's not ok, use a different api for that
please (like a char device node.)
thanks,
greg k-h
On Sun, Sep 03, 2023 at 06:04:23AM PDT, Greg Kroah-Hartman wrote:
>On Fri, Sep 01, 2023 at 02:13:23AM -0700, Zev Weiss wrote:
>> Adding Greg re: sysfs ABI design...
>>
>> On Thu, Aug 31, 2023 at 05:14:10AM PDT, Naresh Solanki wrote:
>> > Adds sysfs-driver-regulator-output
>> >
>> > Signed-off-by: Naresh Solanki <[email protected]>
>> > ---
>> > .../ABI/testing/sysfs-driver-regulator-output | 11 +++++++++++
>> > 1 file changed, 11 insertions(+)
>> > create mode 100644 Documentation/ABI/testing/sysfs-driver-regulator-output
>> >
>> > diff --git a/Documentation/ABI/testing/sysfs-driver-regulator-output b/Documentation/ABI/testing/sysfs-driver-regulator-output
>> > new file mode 100644
>> > index 000000000000..f9b0a8f810fa
>> > --- /dev/null
>> > +++ b/Documentation/ABI/testing/sysfs-driver-regulator-output
>> > @@ -0,0 +1,11 @@
>> > +What: /sys/bus/platform/drivers/regulator-output/*/events
>> > +Date: August 2023
>> > +Description: Provided regulator events.
>> > +
>> > + Read provides various events the regulator associated with the
>> > + driver has encountered. All REGULATOR_EVENT_* are
>> > + defined in include/uapi/linux/regulator.h
>> > +
>> > + e.g.
>> > + cat /sys/bus/platform/drivers/regulator-output/ssb_rssd32/events
>> > + 0x0
>>
>> If we really are going to proceed with a "read with side-effects"
>> (clear-on-read) design, that should absolutely be loudly and clearly
>> documented, since it's very different from how sysfs files typically work
>> and hence a somewhat glaring principle-of-least-surprise violation. Also,
>> since from the code it looks like it's intended to be used via poll(2), that
>> should be described here as well.
>
>Poll? Ick, but that can happen.
>
>But yes, reading a sysfs should almost never cause a side affect at all.
>
>But what do you mean by "clear events?"
I mean that when the sysfs file is read, the state variable whose value
it exposes is also cleared as a side-effect (so the read operation
"consumes" the value it returns) -- see the implementation in patch 2 of
this series (specifically the 'data->events = 0' assignment in
events_show()):
https://lore.kernel.org/lkml/[email protected]/
(As indicated in my reply to that patch, this seems like a footgun to me
and I'm hoping we can come up with a better approach.)
Zev