Implement epoll for FS#27201
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sbc100
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Jun 26, 2026
Implements epoll_create1/epoll_ctl/epoll_wait/epoll_pwait in the JS syscall layer on a unified fd-readiness wait-queue shared with poll(). - epoll instances are real FS fds, so close(2) and nesting work for free - level- and edge-triggered (EPOLLET), EPOLLONESHOT, EPOLLRDHUP, and the EPOLLEXCLUSIVE ctl restriction (its wakeup-limiting is a no-op, single- threaded; only the EPOLL_CTL_MOD restriction is enforced) - blocking epoll_wait suspends under PROXY_TO_PTHREAD, ASYNCIFY and JSPI - sockets and pipes feed readiness via a producer wait-queue - WASMFS epoll is out of scope (fails at link time) Only sockets and pipes derive real readiness; every other stream type (regular files across MEMFS/NODEFS/NODERAWFS, devices, ttys) has no poll handler and is treated as always readable+writable, so epoll_ctl rejects it with EPERM. This also fixes poll() crashing on a NODERAWFS regular file, whose stream carries no stream_ops at all. Known limitation: as before, ttys are not pollable (no poll handler), unlike Linux.
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Could you split this PR in to two parts:
We should be able to land (1) right away then we can focus on reviewing (2) .. which might take a little longer. |
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Sure, I can post the two separate PRs instead. Let me do that. |
sbc100
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Jun 26, 2026
This adds the epoll syscall surface (headers, libc wrappers, declarations and signatures) with no working implementation, so the boilerplate can land ahead of the host integration. Split out from #27201 so that the larger, more involved host implementation can be reviewed separately. The syscalls are fully wired in but return `-ENOSYS` everywhere for now: * `sys/epoll.h` synced from upstream musl, and removed from the exclude list in `update_musl.py` * musl `epoll.c` wrappers compiled into libc (`epoll_create`/`epoll_create1`/`epoll_ctl`/`epoll_wait`/`epoll_pwait`) * `SYS_epoll_*` -> `__syscall_epoll_*` mappings, declarations in `emscripten/syscalls.h`, and `libsigs.js` signatures * legacy (non-WASMFS) JS `__syscall_epoll_*` return `-ENOSYS` * WASMFS `__syscall_epoll_*` return `-ENOSYS`, matching the existing socket stubs in `syscalls.cpp` * `tools/native_sigs.py` regenerated for the new libc functions The actual readiness/wait-queue host integration (the working epoll) follows in a separate PR.
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Resolves #5033, #10556.
With all the poll work, it kind of makes sense to just implement actual epoll at this point for compat and the extra functionality.
This adds the functions -
epoll_create1,epoll_ctl,epoll_wait,epoll_pwait.With
-sNODERAWSOCKETSand-SNODERAWFSthis allows real epolling on the file descriptors, without the once-style semantics ofpoll()being a requirement.In the process this includes some of the refactorings from #27181 in unifying the notification / listener system for JS.
Supports
EPOLLONESHOT, butEPOLLEXCLUSIVEis effectively ignored for the pthreads case still currently.It does not yet support epoll for WASMFS, which would be a follow-on.
PR made with AI assistance, under my review