Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels enabled to be activated

[Lars-Peter Clausen]

On 3/26/20 8:42 AM, Ardelean, Alexandru wrote:
> On Wed, 2020-03-25 at 17:57 +0200, Andy Shevchenko wrote:
> > [External]
> >
> > On Wed, Mar 25, 2020 at 12:02 PM Alexandru Ardelean
> > <alexandru.ardelean@xxxxxxxxxx> wrote:
> > > From: Lars-Peter Clausen <lars@xxxxxxxxxx>
> > >
> > > Before activating a buffer make sure that at least one channel is enabled.
> > > Activating a buffer with 0 channels enabled doesn't make too much sense and
> > > disallowing this case makes sure that individual driver don't have to add
> > > special case code to handle it.
> > >
> > > Currently, without this patch enabling a buffer is possible and no error is
> > > produced. With this patch -EINVAL is returned.
> > >
> > > An example of execution with this patch and some instrumented print-code:
> > >     root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> > >     root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
> > >     0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer-
> > > > scan_mask 00000000
> > >     1: iio_verify_update 753
> > >     2:__iio_update_buffers 1115 ret -22
> > >     3: iio_buffer_store_enable 1241 ret -22
> > >     -bash: echo: write error: Invalid argument
> > > 1, 2 & 3 are exit-error paths. 0 the first print in iio_verify_update()
> > > rergardless of error path.
> > >
> > > Without this patch (and same instrumented print-code):
> > >     root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> > >     root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
> > >     0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer-
> > > > scan_mask 00000000
> > >     root@analog:/sys/bus/iio/devices/iio:device3/buffer#
> > > Buffer is enabled with no error.
> > >
> > > Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> > > ---
> > >
> > > Changelog v1 -> v2:
> > > * moved check in iio_verify_update()
> > > * added dev_dbg() message; should help some folks understand the message
> > > * documented steps to reproduce
> > > * added Fixes tag; hopefully the tag is the good one; if needed, it can be
> > >    dropped; this has been around for ~8 years; no idea if it's worth
> > >    backporting
> > Where?
> stable/fixes/lts-kernels
> don't have a really good clue about where these things need backporting;
What Andy means is that there is no Fixes tag :)