diff --git a/lsusb/main.go b/lsusb/main.go index 1da2199..5be0f3d 100644 --- a/lsusb/main.go +++ b/lsusb/main.go @@ -9,40 +9,60 @@ import ( "github.com/kylelemons/gousb/usbid" ) -var ( - ctx = usb.NewContext() -) - var ( debug = flag.Int("debug", 0, "libusb debug level (0..3)") ) func main() { flag.Parse() + + // Only one context should be needed for an application. It should always be closed. + ctx = usb.NewContext() + defer ctx.Close() + + // Debugging can be turned on; this shows some of the inner workings of the libusb package. ctx.Debug(*debug) - devs, err := ctx.ListDevices(func(bus, addr int, desc *usb.Descriptor) bool { return true }) + // ListDevices is used to find the devices to open. + devs, err := ctx.ListDevices(func(bus, addr int, desc *usb.Descriptor) bool { + // After inspecting the descriptor, return true or false depending on whether + // the device is "interesting" or not. Any descriptor for which true is returned + // generates a DeviceInfo which is retuned in a slice. + return true + }) + + // All DeviceInfo returned from ListDevices must be closed. defer func() { for _, d := range devs { d.Close() } }() + + // ListDevices can occaionally fail, so be sure to check its return value. if err != nil { log.Fatalf("list: %s", err) } for _, dev := range devs { + // The descriptor (which contains useful information) can always be obtained again + // from a DeviceInfo. desc, err := dev.Descriptor() if err != nil { log.Printf("desc: %s", err) continue } + + // The DeviceInfo contains the bus number and bus address of the device. bus := dev.BusNumber() addr := dev.Address() + // The usbid package can be used to print out human readable information. fmt.Printf("%03d:%03d %s\n", bus, addr, usbid.Describe(desc)) fmt.Printf(" Protocol: %s\n", usbid.Classify(desc)) + // The configurations can be examined from the DeviceInfo, though they can only + // be set once the device is opened. All configuration references must be closed, + // to free up the memory in libusb. cfgs, err := dev.Configurations() defer func() { for _, cfg := range cfgs { @@ -54,6 +74,8 @@ func main() { continue } + // This loop just uses more of the built-in and usbid pretty printing to list + // the USB devices. for _, cfg := range cfgs { fmt.Printf(" %s:\n", cfg) for _, alt := range cfg.Interfaces { @@ -68,5 +90,8 @@ func main() { } fmt.Printf(" --------------\n") } + + // To actually interact with a device, DevInfo.Open() returns a device handle + // which can be used to do more I/O with the device and its endpoints. } } diff --git a/usb/config.go b/usb/config.go index 2dfb7cf..962d6a2 100644 --- a/usb/config.go +++ b/usb/config.go @@ -131,6 +131,9 @@ func newConfig(cfg *C.struct_libusb_config_descriptor) *Config { // Close decrements the reference count for the device in the libusb driver // code. It should be called exactly once! +// +// TODO(kevlar): This information can probably be cached at creation time +// and then immediately closed. func (c *Config) Close() error { if c.cfg != nil { //log.Printf("config %p closed", c.cfg)