Savestates don't handle file descriptors

[clementgallet]

Loading a savestate does not recover the positions in file descriptors. This leads to crashes in games that use files continuously, for example games like Deltarune or Hyper Light Drifter that use OGG decompression on the fly (I'm getting ov_read error: -3).

An even worse problem is that loading a savestate won't be able to reopen closed files, because we are not guaranteed to obtain the same file descriptor. I don't have a good solution to this. It is still possible to:

• Keep every single file opened, even if the game closes them. This would solve our problem, except that we may hit the maximum of concurrently opened files (1024 per process on my system). We could raise this limit, but is it a good thing to do? We also could do this in a smart way, only keeping track of files that were opened during a savestate.
• Keep a structure that translates real system fds to game (fake) fds. For each function using a fd that the game calls, we translate this fd into the real system fd. This way, we can safely create fds when loading a savestate, and register the translation. However, this would lead to a serious overhead (hooking read() and write() does not sound like a good idea).

Edit: Well, solution 1 seems realistic after all.

[clementgallet]

I'm quite happy this this solution (f8d2394a0a7aa9d067d1803885d2207594fd48cd). It looks like it solves the problem in the above games. There is still a small problem resulting in lost fds in the following case:

1. user makes savestate 1
2. the game opens a file
3. user makes savestate 2, the file is tracked
4. user loads savestate 1, the file is still opened, in case the user wants to load savestate 2
5. the game opens the same file as above, but we are getting a new file descriptor
6. user makes savestate 2, the new file is tracked, but we lost all references to the old file descriptor