Closing a device file takes 0.01 to 0.5s, which can add up to
significant startup delays. The udev classification does not
require opening the actual device files, so, use it if possible,
and only fall back to opening the device and probing otherwise.
LINUX_JoystickInit does a manual scan first so devices are sorted.
If SDL_UDEV_Init hasn't run by then, then the product info cannot
be looked up by SDL_UDEV_GetProductInfo and the initial-plugged-
in-device classification falls back to heuristic guessing.
I believe there was a O(n^2) device walking issues on startup
- MaybeAddDevice gets called for every device at startup
- MaybeAddDevice calls IsJoystick
- IsJoystick calls SDL_UDEV_GetProductInfo
- SDL_UDEV_GetProductInfo calls udev_enumerate_scan_devices
- udev_enumerate_scan_devices walks all the devices
Prior to commit 3b1e0e1 this was mostly masked as IsJoystick only
called SDL_UDEV_GetProductInfo when a JSIOCGNAME ioctl was
successful. This fixes the O(n^2) behaviour by directly getting
the device via udev_device_new_from_devnum (based on type, major,
and minor number) instead of enumerating everything via
udev_enumerate_scan_devices and matching on name.
The udev container issue is mostly to do with device notifications
and netlink. The device classification stuff just pokes file in /sys
and /run/udev. Doesn't hurt to try it first for classifying joysticks
and then fall to the guess heuristics if it fails.
Tyson Whitehead