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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Bump bundled libuv to ≥1.49 so io_uring isn't silently on by default","articleBody":"## Problem\n\n`uvloop` vendors libuv 1.48.0 (`vendor/libuv` submodule SHA `e9f29cb9…` → tag v1.48.0, 2024-02-07). On kernels ≥ 5.10.186 that libuv turns on io_uring **by default** — an `IORING_SETUP_SQPOLL` ring for async file ops and an `IORING_OP_EPOLL_CTL` batching ring for `epoll_ctl`. Nothing in the stack opts in:\n\n```\napp → uvloop.run() → uvloop → bundled libuv 1.48 → io_uring_enter\n```\n\nObserved via an eBPF tracepoint on `io_uring_setup`/`io_uring_enter`: uvloop-driven processes issue those syscalls during normal startup, before any app file I/O.\n\n## Why\n\nio_uring bypasses the syscall boundary seccomp filters on. Ops inside the ring (openat, read, write, connect) aren't individual syscalls — seccomp can only allow/deny `io_uring_enter` wholesale, not the ops inside. So if you relax the profile to silence the inevitable EPERM noise, you punch a hole through the whole seccomp profile. The default Kubernetes `RuntimeDefault` profile denies `io_uring_setup` (#426), which is correct — but means uvloop-driven processes noisily fail into libuv's epoll+threadpool fallback on every loop init.\n\nlibuv already agreed: **v1.49.0 disabled SQPOLL io_uring by default** (#4492). The gap isn't libuv — it's consumers still bundling 1.48.\n\nuvloop is the layer that controls io_uring exposure for most of the Python ecosystem (via `uvicorn[standard]` → uvloop). Today that choice is \"io_uring on by default, suppressed only by seccomp.\"\n\n## Proposal\n\n1. **Bump `vendor/libuv` to ≥ 1.49.0.** Consistent with prior uvloop libuv bumps (v0.15.0, v0.14.0, etc.). Removes the SQPOLL ring from the default footprint.\n2. **Document** the io_uring behavior + the `UV_USE_IO_URING=0` escape hatch in the README. (Note: the env var fully gates io_uring in 1.48; in 1.49+ the `IORING_OP_EPOLL_CTL` batching ring is no longer gated by it — verify against whatever version you ship.)\n3. Optionally expose a uvloop-level switch (`UVLOOP_USE_IO_URING=0`) so apps don't have to reach into libuv's env var.\n\n## References\n\n- libuv v1.49.0 (2024-09-25): https://github.com/libuv/libuv/releases/tag/v1.49.0 — \"linux: disable SQPOLL io_uring by default #4492\"\n- libuv v1.48.0 (2024-02-07): https://github.com/libuv/libuv/releases/tag/v1.48.0 — what uvloop currently bundles\n- PR #4492: https://github.com/libuv/libuv/pull/4492","author":{"url":"https://github.com/hixichen","@type":"Person","name":"hixichen"},"datePublished":"2026-06-23T18:31:37.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/752/uvloop/issues/752"}