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event.go
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event.go
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//go:build linux
// +build linux
/*
Package event provides access to system-level event file descriptors that act as semaphores and
notification mechanism to facilitate AF_PACKET network traffic capture. This is achieved either via
conventional recvfrom() operations (per-packet retrieval in afpacket/afpacket) or via PPOLL and
the kernel ring buffer (per-block retrieval in afpacket/afring).
In the latter case, a highly optimized assembler implementation is used (for AMD64 / ARM64 architectures)
in order to maximize throughput (by releasing resources as early as possible for the next poll operation).
*/
package event
import (
"fmt"
"golang.org/x/sys/unix"
)
// EvtFileDescriptor denotes a system-level event file descriptor
type EvtFileDescriptor int
// EvtData denotes the data sent / received during an event
type EvtData [8]byte
var (
// SignalUnblock ends any ongoing PPOLL syscall (similar to a timeout)
SignalUnblock = EvtData{1, 0, 0, 0, 0, 0, 0, 0}
// SignalStop causes the capture to stop
SignalStop = EvtData{0, 0, 0, 0, 0, 0, 0, 1}
)
// New instantiates a new non-blocking event file descriptor
func New() (EvtFileDescriptor, error) {
efd, err := unix.Eventfd(0, unix.EFD_NONBLOCK)
if err != nil {
return -1, fmt.Errorf("failed to create event file descriptor: %w", err)
}
return EvtFileDescriptor(efd), nil
}
// Signal sends an event via the event file descriptor
func (e EvtFileDescriptor) Signal(data EvtData) error {
n, err := unix.Write(int(e), data[:])
if err != nil {
return fmt.Errorf("failed to send event: %w", err)
}
if n != len(data) {
return fmt.Errorf("failed to send event (unexpected number of bytes written, want %d, have %d)", len(data), n)
}
return nil
}
// ReadEvent reads the event data from the event file descriptor
func (e EvtFileDescriptor) ReadEvent() (EvtData, error) {
var data EvtData
n, err := unix.Read(int(e), data[:])
if err != nil {
return data, fmt.Errorf("failed to read event data: %w", err)
}
if n != len(data) {
return data, fmt.Errorf("failed to read event data (unexpected number of bytes read, want %d, have %d)", len(data), n)
}
return data, nil
}