Re: [PATCH v4 00/13] gpiolib: add an ioctl() for monitoring line status changes

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, Dec 24, 2019 at 1:07 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:

> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
>
> When discussing the recent user-space changes with Kent and while working
> on dbus API for libgpiod I noticed that we really don't have any way of
> keeping the line info synchronized between the kernel and user-space
> processes. We can of course periodically re-read the line information or
> even do it every time we want to read a property but this isn't optimal.
>
> This series adds a new ioctl() that allows user-space to set up a watch on
> the GPIO chardev file-descriptor which can then be polled for events
> emitted by the kernel when the line is requested, released or its status
> changed. This of course doesn't require the line to be requested. Multiple
> user-space processes can watch the same lines.
>
> This series also includes a variety of minor tweaks & fixes for problems
> discovered during development. For instance it addresses a race-condition
> in current line event fifo.

The patch set overall looks good to me, I don't understand the kfifo
parts but I trust you on this, though we need review from a FIFO
maintainer.

Could you send me a pull request of the first patches before the
FIFO changes start, they are good cleanups on their own, also
it brings down the size of your patch stack.

Yours,
Linus Walleij