Module signalfd 

signalfd – Signal notification file descriptor

Provides a file descriptor for receiving signals via read(2) instead of signal handlers. Integrable with epoll/poll for unified I/O event loops. Used by D-Bus daemon and systemd-compatible service managers.

Syscall Interface

• signalfd_create(fd, mask_ptr, mask_size, flags) -> fd (syscall 334)
• Read via standard read(2) on returned fd

Semantics

• read: Returns one or more SignalfdSiginfo structs (128 bytes each) for pending signals in the mask. Signals consumed by signalfd are removed from the process’s pending set.
• Creating with fd == -1 creates a new signalfd; passing an existing fd updates the signal mask.

Structs

SigSet

Signal mask – a bitmask of signal numbers to monitor.

SignalFdNode

VfsNode wrapper around a signalfd instance.

SignalfdSiginfo

Signal information returned by read(2) on a signalfd. Matches Linux’s struct signalfd_siginfo layout (128 bytes).

Constants

SFD_CLOEXEC

SFD_CLOEXEC: Set close-on-exec.

SFD_NONBLOCK

SFD_NONBLOCK: Return EAGAIN instead of blocking on empty read.

Functions

deliver_signal

Deliver a signal to all signalfds of a given process that have the signal in their mask.

is_readable

Query whether a signalfd has pending signals. Used by epoll to check readiness without consuming data.

signalfd_close

Close (destroy) a signalfd instance.

signalfd_create

Create or update a signalfd.

signalfd_read

Read one pending signal from a signalfd.