adjust S_IFIFO to avoid collisions

[vapier]

S_IFIFO currently has the same value as S_IFSOCK which breaks code
that does things like "switch (mode & S_IFMT)" as we end up with
duplicate labels. Move S_IFIFO to a unique unused value.

[vapier]

i guess more importantly, the current defines make it impossible to differentiate between fifos & sockets :)

[sunfishcode]

The catch here is that WASI itself doesn't currently have a file type for fifos, so it can't currently distinguish between fifos and sockets. This comes from CloudABI. It was removed here.

At an initial glance, I think it would make sense to add a FIFO filetype to WASI. Even if WASI doesn't support creating new FIFOs right now, and even though FIFOs aren't an entirely portable construct, WASI programs can interact with FIFOs when they do happen to be present. And it can be useful to distinguish between socket and fifo, since you can't openat a socket.

@vapier Would you mind filing a PR to the WASI repo, modifying the typenames.witx file linked above, to add a __WASI_FILETYPE_FIFO? Once we have that, we can add proper libc support.

I guess there's also the question of whether we should land this patch as-is right now. How big of a problem is it if fifos aren't reported as S_IFIFO?

[vapier]

all of that sounds fine. i'll try to tackle it when i get a chance. thx!

[vapier]

i posted WebAssembly/WASI#189 to add FIFO filetype

[vapier]

my WASI PR is merged now. was there something else needed here before merging?

[sunfishcode]

Before we merge changes into wasi-libc which WASI implementations will need to support, we'll need the WASI Subgroup to publish a new snapshot. There isn't a specific schedule for that yet, but it hopefully won't be too long.

[vapier]

i think a new snapshot has been posted by now ? so can we merge ?

[sunfishcode]

Unfortunately no, we have not published a new snapshot yet. Snapshot 2 is set to include modularization, which requires updates to the witx tooling, which is not finished yet. Hopefully once we're past this milestone, subsequent snapshots can be published more frequently.