strace decoding for GPIO uAPI

[Kent Gibson <warthog618@xxxxxxxxx>]

On Tue, Sep 22, 2020 at 11:50:51AM +0200, Bartosz Golaszewski wrote:
> On Tue, Sep 22, 2020 at 9:41 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> >
> > On Tue, Sep 22, 2020 at 4:34 AM Kent Gibson <warthog618@xxxxxxxxx> wrote:
> > > +/**
> >
> > Having different-sized members in the union makes it hard for
> > something like strace to print the contents. How about just making
> > them all __aligned_u64 even when 32 bits are sufficient?
> >
> 
> Ah yes, adding support for GPIO ioctl()'s to strace has been on my
> TODO list for 3 years now. :(
> 

I'm looking at doing this as it would be useful to have.

Just starting with the v1 uAPI, as v2 isn't merged yet.

I think I've got it basically done, but I thought I'd run it past you
before sending a patch to the strace list.

Successful calls currently look like this:

ioctl(3, GPIO_GET_CHIPINFO_IOCTL, {name="gpiochip1", label="gpio-mockup-B", lines=8}) = 0

ioctl(3, GPIO_GET_LINEHANDLE_IOCTL, {lines=8, lineoffsets=[3, 2, 1, 0, 4, 5, 6, 7], flags=GPIOHANDLE_REQUEST_INPUT, default_values=[0, 0, 0, 0, 0, 0, 0, 0], consumer_label="", fd=7}) = 0

ioctl(0, GPIO_GET_LINEEVENT_IOCTL, {lineoffset=2, handleflags=GPIOHANDLE_REQUEST_INPUT, eventflags=GPIOEVENT_REQUEST_BOTH_EDGES, consumer_label="high to low", fd=3}) = 0

ioctl(3, GPIO_GET_LINEINFO_IOCTL, {line_offset=1, flags=GPIOLINE_FLAG_KERNEL|GPIOLINE_FLAG_IS_OUT, name="gpio-mockup-A-1", consumer="output atv-lo to as-is atv-hi"}) = 0

ioctl(7, GPIOHANDLE_GET_LINE_VALUES_IOCTL, {values=[1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...]}) = 0

ioctl(7, GPIOHANDLE_SET_LINE_VALUES_IOCTL, {values=[1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...]}) = 0

ioctl(7, GPIOHANDLE_SET_CONFIG_IOCTL, {flags=GPIOHANDLE_REQUEST_ACTIVE_LOW, default_values=[0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...]}) = 0

ioctl(3, GPIO_GET_LINEINFO_WATCH_IOCTL, {line_offset=3, flags=0, name="gpio-mockup-A-3", consumer=""}) = 0

ioctl(3, GPIO_GET_LINEINFO_UNWATCH_IOCTL, {offset=3}) = 0

For unsuccessful calls it only prints the input fields, and drops the
output fields. e.g. 

ioctl(3, GPIO_GET_LINEINFO_WATCH_IOCTL, {line_offset=3}) = -1 EPERM (Operation not permitted)

Does that work for you?

Cheers,
Kent.