udev.go

// +build linux,cgo

// Package udev provides a cgo wrapper around the libudev C library
package udev

/*
  #cgo LDFLAGS: -ludev
  #include <libudev.h>
  #include <linux/types.h>
  #include <stdlib.h>
	#include <linux/kdev_t.h>
*/
import "C"
import (
	"runtime"
	"sync"
)

// Udev is an opaque struct wraping a udev library context
type Udev struct {
	// A pointer to the C struct udev context
	ptr *C.struct_udev
	// Mutex for thread sync as libudev is not thread safe when called with the same struct udev
	m    sync.Mutex
	once sync.Once
}

func udevUnref(u *Udev) {
	C.udev_unref(u.ptr)
}

// Lock locks a udev context
func (u *Udev) lock() {
	u.once.Do(func() {
		u.ptr = C.udev_new()
		runtime.SetFinalizer(u, udevUnref)
	})
	u.m.Lock()
}

// Unlock unlocks a udev context
func (u *Udev) unlock() {
	u.m.Unlock()
}

// newDevice is a private helper function and returns a pointer to a new device.
// The device is also added t the devices map in the udev context.
// The agrument ptr is a pointer to the underlying C udev_device structure.
// The function returns nil if the pointer passed is NULL.
func (u *Udev) newDevice(ptr *C.struct_udev_device) (d *Device) {
	// If passed a NULL pointer, return nil
	if ptr == nil {
		return nil
	}
	// Create a new device object
	d = &Device{
		ptr: ptr,
		u:   u,
	}
	runtime.SetFinalizer(d, deviceUnref)
	// Return the device object
	return
}

// newMonitor is a private helper function and returns a pointer to a new monitor.
// The monitor is also added t the monitors map in the udev context.
// The agrument ptr is a pointer to the underlying C udev_monitor structure.
// The function returns nil if the pointer passed is NULL.
func (u *Udev) newMonitor(ptr *C.struct_udev_monitor) (m *Monitor) {
	// If passed a NULL pointer, return nil
	if ptr == nil {
		return nil
	}
	// Create a new device object
	m = &Monitor{
		ptr: ptr,
		u:   u,
	}
	runtime.SetFinalizer(m, monitorUnref)
	// Return the device object
	return
}

func (u *Udev) newEnumerate(ptr *C.struct_udev_enumerate) (e *Enumerate) {
	// If passed a NULL pointer, return nil
	if ptr == nil {
		return nil
	}
	// Create a new device object
	e = &Enumerate{
		ptr: ptr,
		u:   u,
	}
	runtime.SetFinalizer(e, enumerateUnref)
	// Return the device object
	return
}

// NewDeviceFromSyspath returns a pointer to a new device identified by its syspath, and nil on error
// The device is identified by the syspath argument
func (u *Udev) NewDeviceFromSyspath(syspath string) *Device {
	// Lock the udev context
	u.lock()
	defer u.unlock()
	// Convert Go strings to C strings for passing
	s := C.CString(syspath)
	defer freeCharPtr(s)
	// Return a new device
	return u.newDevice(C.udev_device_new_from_syspath(u.ptr, s))
}

// NewDeviceFromDevnum returns a pointer to a new device identified by its Devnum, and nil on error
// deviceType is 'c' for a character device and 'b' for a block device
func (u *Udev) NewDeviceFromDevnum(deviceType uint8, n Devnum) *Device {
	u.lock()
	defer u.unlock()
	return u.newDevice(C.udev_device_new_from_devnum(u.ptr, C.char(deviceType), n.d))
}

// NewDeviceFromSubsystemSysname returns a pointer to a new device identified by its subystem and sysname, and nil on error
func (u *Udev) NewDeviceFromSubsystemSysname(subsystem, sysname string) *Device {
	u.lock()
	defer u.unlock()
	ss, sn := C.CString(subsystem), C.CString(sysname)
	defer freeCharPtr(ss)
	defer freeCharPtr(sn)
	return u.newDevice(C.udev_device_new_from_subsystem_sysname(u.ptr, ss, sn))
}

// NewDeviceFromDeviceID returns a pointer to a new device identified by its device id, and nil on error
func (u *Udev) NewDeviceFromDeviceID(id string) *Device {
	u.lock()
	defer u.unlock()
	i := C.CString(id)
	defer freeCharPtr(i)
	return u.newDevice(C.udev_device_new_from_device_id(u.ptr, i))
}

// NewEnumerate returns a pointer to a new enumerate, and nil on error
func (u *Udev) NewEnumerate() *Enumerate {
	u.lock()
	defer u.unlock()
	return u.newEnumerate(C.udev_enumerate_new(u.ptr))
}

// NewMonitorFromNetlink returns a pointer to a new monitor listening to a NetLink socket, and nil on error
// The name argument is either "kernel" or "udev".
// When passing "kernel" the events are received before they are processed by udev.
// When passing "udev" the events are received after udev has processed the events and created device nodes.
// In most cases you will want to use "udev".
func (u *Udev) NewMonitorFromNetlink(name string) *Monitor {
	u.lock()
	defer u.unlock()
	n := C.CString(name)
	defer freeCharPtr(n)
	return u.newMonitor(C.udev_monitor_new_from_netlink(u.ptr, n))
}

/*
// NewMonitorFromSocket returns a pointer to a new monitor listening to the specified socket, and nil on error
func (u *Udev) NewMonitorFromSocket(socketPath string) *Monitor {
	u.lock()
	defer u.unlock()
	s := C.CString(socketPath)
	defer freeCharPtr(s)
	return u.newMonitor(C.udev_monitor_new_from_socket(u.ptr, s))
}
*/