[PATCH 2/4] Add GPIO ioctl decoding

[Kent Gibson]

On Wed, Dec 30, 2020 at 12:47:28PM +0300, Dmitry V. Levin wrote:
> On Wed, Dec 30, 2020 at 10:58:14AM +0800, Kent Gibson wrote:
> > On Wed, Dec 30, 2020 at 05:07:42AM +0300, Dmitry V. Levin wrote:
> > > On Wed, Dec 23, 2020 at 06:07:46AM +0800, Kent Gibson wrote:
> > > > Decode the GPIO character device ioctls first introduced in Linux v4.8,
> > > > as well as those added in subsequent kernel releases up to Linux v5.7.
> > > > 
> > > > Signed-off-by: Kent Gibson <warthog618 at gmail.com>
> > > [...]
> > 
> > [...]
> > > > +	PRINT_FIELD_U("{", info, line_offset);
> > > > +	if (!tcp->u_rval) {
> > > > +		tprints(", flags=");
> > > > +		printflags(gpio_line_flags, info.flags, "GPIOLINE_FLAG_???");
> > > > +		PRINT_FIELD_CSTRING(", ", info, name);
> > > > +		PRINT_FIELD_CSTRING(", ", info, consumer);
> > > > +	}
> > > > +	tprints("}");
> > > 
> > > Both GPIO_GET_LINEINFO_IOCTL and GPIO_GET_LINEINFO_WATCH_IOCTL are
> > > read-write ioctls, that is, the kernel reads struct gpioline_info on
> > > entering syscall and writes it back on exiting.  A comprehensive decoder
> > > would do the same, i.e. print the relevant parts of the structure both on
> > > entering and on exiting.  There would be no need to use
> > > umove_or_printaddr_ignore_syserror and ignore syscall errors.
> > > 
> > 
> > Sorry I don't have prompt replies for your other comments - this code has
> > been sitting in my working tree for months as I was having problems
> > mailing to the list back then so I'll have to spend some time recapturing
> > what I was thinking while writing it.
> > 
> > A decoder can't be comprehensive if it is only decoding relevant parts ;-).
> > 
> > So should the decoder decode the full struct both ways, or just the fields
> > the kernel reads on the way in and the fields it wrote on the way out?
> 
> There is no need to print the full struct two times, only those fields
> that could be accessed by the kernel.
> 

Is this the sort of thing you are after for the IOWRs?:

[pid   107] ioctl(3, GPIO_GET_LINEINFO_IOCTL, {line_offset=2} => {flags=GPIOLINE_FLAG_KERNEL, name="gpio-mockup-A-2", consumer="test-as-is"}) = 0

I'm using this idiom to decode it:

static int
print_gpioline_info(struct tcb *const tcp, const kernel_ulong_t arg)
{
	struct gpioline_info info;

	if (entering(tcp)) {
		tprints(", ");
		if (umove_or_printaddr(tcp, arg, &info))
			return RVAL_IOCTL_DECODED;

		PRINT_FIELD_U("{", info, line_offset);
		tprints("}");
		return 0;
	}

	/* exiting */
    if (!syserror(tcp) && !umove(tcp, arg, &info)) {
		tprints(" => {flags=");
		printflags(gpio_line_flags, info.flags, "GPIOLINE_FLAG_???");
		PRINT_FIELD_CSTRING(", ", info, name);
		PRINT_FIELD_CSTRING(", ", info, consumer);
		tprints("}");
	}

	return RVAL_IOCTL_DECODED;
}

If that works for you I'll rework the rest similarly.

Cheers,
Kent.