Daan De Meyer
7bc793e21f
Some helpers in src/basic — ppoll_usec_full() (used by fd_wait_for_event()), loop_read(), loop_read_exact(), loop_write_full() and pidref_wait_for_terminate_full() — block the calling thread. That's the right behaviour outside a fiber but not inside one, where blocking the thread also stalls every other fiber running on the same event loop. Rewriting every caller to pick a fiber or non-fiber variant explicitly would be a lot of churn and would split otherwise-shared code paths in two. Instead, the helpers detect at runtime whether they're running on a fiber and dispatch to a suspending variant when they are. FiberOps in fiber-ops.h holds five function pointers (ppoll, read, write, timeout, cancel_wait_unref); a fiber_ops global constant is populated whenever we enter a fiber with functions that delegate to suspending variants of common syscalls. With this approach, the variants themselves stay in libsystemd which is required because they make use of sd-event. - loop_read()/loop_read_exact() take the fiber read hook on a fiber unless the caller asked for a non-blocking attempt (do_poll=false) and the fd is already non-blocking — in that case we fall through to read() to preserve the existing return-EAGAIN-immediately semantic. The hook itself suspends on EAGAIN until data is available, so neither the do_poll knob nor the explicit fd_wait_for_event() retry loop are needed on the fiber path. - loop_write_full() likewise takes the fiber write hook on a fiber, except when timeout=0 with an already-non-blocking fd (preserving the fast-return-EAGAIN semantic). The fiber path runs inside a FIBER_OPS_TIMEOUT() scope so the caller's timeout is honoured via a deadline future, mirroring SD_FIBER_TIMEOUT() but reachable from src/basic without pulling in sd-future.h. - pidref_wait_for_terminate_full() polls the pidfd via fd_wait_for_event() before each waitid() when either a finite timeout is set or we're on a fiber, and requires pidref->fd >= 0 in those cases (returning -ENOMEDIUM otherwise — extending the rule that already applied to finite timeouts). The poll suspends the fiber via the ppoll hook above; the subsequent waitid() doesn't block because the pidfd is already signalled.
System and Service Manager
Details
Most documentation is available on systemd's web site.
Assorted, older, general information about systemd can be found in the systemd Wiki.
Information about build requirements is provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the Code Map for information about this repository's layout and content.
Please see the Hacking guide for information on how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list, join our IRC channel #systemd on libera.chat or Matrix channel
Stable branches with backported patches are available in the stable repo.
We have a security bug bounty program sponsored by the Sovereign Tech Fund hosted on YesWeHack
Repositories with distribution packages built from git main are available on OBS, and also repositories with packages built from the latest stable release