Handle O_NONBLOCK about p9

[hugelgupf]

You have a good point. gVisor always assumed that all file system ops are non-blocking (and implemented blocking ops on top of that on the client side), so we built that assumption into the library.

[hugelgupf]

I'm looking into this right now. I don't think it's the O_NONBLOCK, but I'm having to write some debugging tools before I can figure out what it actually is.

[hugelgupf]

Turning on debug output, there ended up being two problems:

2019/09/01 17:15:46 recv [conn 0xc00009e028] [Tag 000002] Twalk{FID: 1, newFID: 3, Names: []}                                                                                                   
2019/09/01 17:15:46 send [conn 0xc00009e028] [Tag 000002] Rlerror{Error: 22}

as the most likely cause for the EINVAL. Let's see where it's coming from.

(in this case, localfs did not allow walking to self. :/)

The other problem was indeed the flags.