fix(ublk-zc): close wake eventfd if ZC thread spawn fails

[jaredLunde]

Problem

Hunting for an fd leak on the ublk happy path turned up one real leak — on an error path adjacent to it.

In start_zc_queue (glidefs/src/block/ublk/device.rs), the cross-thread wake eventfd is created before the ZC queue thread is spawned, but it only becomes owned by ZcThreadGuard after a successful spawn:

let wake_fd = libc::eventfd(...);          // created here
let join = Builder::new().spawn(...)?;     // <-- early return leaks wake_fd
...
let _zc_guard = ZcThreadGuard { wake_fd, ... };  // owner constructed here

If Builder::spawn fails — e.g. resource exhaustion during a multi-device recovery storm, which is exactly when fds are scarce — the ? returns early and leaks one eventfd per queue, because the guard that would close() it is never constructed.

The happy path itself is clean (RawFd is Copy, the thread borrows a copy, the guard closes the canonical fd in Drop). This only bites on spawn failure.

Fix

Wrap wake_fd in an OwnedFd immediately after creation so any early return closes it via Drop, then release ownership to the guard (into_raw_fd) once the spawn succeeds. Ownership semantics on the happy path are unchanged.

🤖 Generated with Claude Code