Module timerfd 

timerfd – Timer notification file descriptor

Provides file descriptors that deliver timer expiration notifications, integrable with epoll/poll. Used by Qt6 for frame pacing and event loop timeouts, and by KWin for compositor frame scheduling.

Syscall Interface

• timerfd_create(clockid, flags) -> fd (syscall 331)
• timerfd_settime(fd, flags, new, old) -> 0 (syscall 332)
• timerfd_gettime(fd, curr) -> 0 (syscall 333)
• Read via standard read(2) on returned fd

Semantics

• read: Returns the number of expirations since last read as a u64. Returns EAGAIN if no expirations and non-blocking, otherwise blocks.
• Timer resolution is based on kernel uptime (TSC-derived).

Structs

Itimerspec

Timer interval specification matching struct itimerspec.

TimerFdNode

VfsNode wrapper around a timerfd instance.

Timespec

Time specification matching struct timespec layout.

Constants

CLOCK_MONOTONIC

CLOCK_REALTIME

Clock IDs (subset of POSIX clocks).

TFD_CLOEXEC

TFD_CLOEXEC: Set close-on-exec.

TFD_NONBLOCK

TFD_NONBLOCK: Return EAGAIN instead of blocking.

TFD_TIMER_ABSTIME

TFD_TIMER_ABSTIME: Interpret new_value.it_value as absolute time.

Functions

is_readable

Query whether a timerfd is readable (timer has expired). Used by epoll to check readiness without consuming data.

timerfd_close

Close (destroy) a timerfd instance.

timerfd_create

Create a new timerfd.

timerfd_gettime

Get the current timer specification.

timerfd_read

Read from a timerfd – returns number of expirations since last read.

timerfd_settime

Arm or disarm a timerfd.