[Wayland-bugs] [Bug 85573] Provide a udev handle from the libinput device

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85573

--- Comment #2 from Bastien Nocera <bugzilla at hadess.net> ---
(In reply to Peter Hutterer from comment #1)
> Main question here: better to get the udev_device handle directly, or the
> device node and leave the rest up to the caller?
> 
> What are the side-effects to each approach?.
> 
> If libinput caches the udev_device handle and returns that, there's some odd
> case where dropping privileges in the caller may give a device the caller
> does not have access to anymore (struggling to find a use-case for that
> though, since it would also break hotplugging).
> 
> If the cached handle is returned, a buggy caller could call
> udev_device_unref too often and cause a (hard to debug) segfault in
> libinput. I'd consider that a normal bug though, can be avoided by returning
> a new handle for the device.

That's quite a flippant approach. If you couldn't depend the caller behaving
properly, you'd get crashes anyway. And valgrind would tell you where the
problem is without a doubt.

> If a new handle is returned, the code isn't much different than returning
> the device node, other than adding another udev dependency on the API. The
> path backend uses udev internally, but returning the device node would be
> simple enough.
> 
> Any new, uncached handle can suffer from race conditions if the device
> disappears. Not much different to normal error handling though.
> Not all devices may have a udev handle, but then again not all devices have
> a device node.

What devices wouldn't have udev handles, and what devices wouldn't have a
device node?

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