On Wed, Oct 26, 2016 at 7:56 PM, Peter Hutterer email@example.com wrote:
On Mon, Oct 17, 2016 at 08:27:32PM -0700, Deepa Dinamani wrote:
struct timeval is not y2038 safe. All usage of timeval in the kernel will be replaced by y2038 safe structures.
struct input_event maintains time for each input event. Real time timestamps are not ideal for input as this time can go backwards as noted in the patch a80b83b7b8 by John Stultz. Hence, having the input_event.time fields only big enough for monotonic and boot times are sufficient.
Leave the original input_event as is. This is to maintain backward compatibility with existing userspace interfaces that use input_event. Introduce a new replacement struct raw_input_event.
general comment here - please don't name it "raw_input_event". First, when you grep for input_event you want the new ones to show up too, so a struct input_event_raw would be better here. That also has better namespacing in general. Second though: the event isn't any more "raw" than the previous we had.
I can't think of anything better than struct input_event_v2 though.
The general idea was to leave the original struct input_event as a common interface for userspace (as it cannot be deleted). So reading raw data unformatted by the userspace will have the new struct raw_input_event format. This was the reason for the "raw" in the name.
struct input_event_v2 is fine too, if this is more preferred.
This replaces timeval with struct input_timeval. This structure maintains time in __kernel_ulong_t or compat_ulong_t to allow for architectures to override types as in the case of x32.
The change requires any userspace utilities reading or writing from event nodes to update their reading format to match raw_input_event. The changes to the popular libraries will be posted along with the kernel changes. The driver version is also updated to reflect the change in event format.
Doesn't this break *all* of userspace then? I don't see anything to negotiate the type of input event the kernel gives me. And nothing right now checks for EVDEV_VERSION, so they all just assume it's a struct input_event. Best case, if the available events aren't a multiple of sizeof(struct input_event) userspace will bomb out, but unless that happens, everyone will just happily read old-style events.
So we need some negotiation what is acceptable. Which also needs to address the race conditions we're going to get when events start coming in before the client has announced that it supports the new-style events.
No, this does not break any userspace right now. Both struct input_event and struct raw_input_event are exactly the same today. This will be the case until a 2038-safe glibc is used with a 64 bit time_t flag.
So these are the scenarios: 1. old kernel driver + new userspace -- should still be ok until 2038. Version checks could help discover these 2. new kernel driver + old userspace (without recompiled with new 2038 gblic) -- works because the format is really the same.
The patch I posted to libevdev checks this driver version. And, hence any library that results in a call to libevdev_set_fd() will fail if it is not this updated driver. We could just do a similar check in every library also. I think the latter would be better.
So, the kernel patches can go in as a no-op right now and then I can add version checks to respective user space libraries.