Update timespec overflow implementation

[LinusCDE]

This was raised by @fenollp when reviewing the rust-impl of this client.

canselcik/libremarkable#78 (comment)

The code wouldn't work properly if SEM_WAIT_TIMEOUT would be greater
than one second, since only one overflow is accounted for with an "if".

Using modulo here instead of while so no branching is needed and it
would scale linearly not not require one loop per overflown second.

(I didn't use 1e9 since it's a double and I'm not sure if it would be perfectly accurate in C++, feel free to change if you don't mind.)

[LinusCDE]

Never mind, changed it back to using 1e9 with casting.

I'm a bit confused as of which impl is used. If glibc/frida's is used over the default one, it should be fine.

The default one according to my (x86_64) linux headers seems like it would be 32 bit on

This would still cause a native overflow issue for delays bigger than ~4.2s as this overflows the 32 bit long on the device.

We will probably not run into an issue in the foreseeable future, but it should still be noted as a possible problem in the implementation.

[LinusCDE]

Edit: The glib/frida impl (glong) actually uses a normal long as well (32 bit) and hence would cause the problem as well.

[LinusCDE]

(The issue could also affect the rust impl as well since it seems that c_long is used for tv_nsec on 32 bit non x86_64 systems)

[alistair23]

tv_nsec should always be a long, see https://linux.die.net/man/3/clock_gettime

The x32 ABI is a strange exception that other architectures don't use.

[alistair23]

Also, it's probably just better to use timeradd to add these: https://man7.org/linux/man-pages/man3/timeradd.3.html

[raisjn]

@alistair23: side question: for the rM1, we think that the wacom driver is drawing power while the device is in deep sleep. would you happen to know how to disable / send the wacom driver (on the i2c bus) a suspend signal or otherwise disable it? (or how to confirm if it is drawing power?) thanks!

[alistair23]

I'm not sure sorry

[LinusCDE]

Also, it's probably just better to use timeradd to add these: https://man7.org/linux/man-pages/man3/timeradd.3.html

Sorry for the late response. This seems probably like the best way. But the current solution should be fine for now. Goes to demonstrate how many levels of better exist for such seemingly a simple task.