Problems with Read - Linux /dev/input/event*

[Dan Anderson]

Trying to read raw evdev events from my keyboard -> /dev/input/event0, using the following code:

func main() {

kbd, _ := os.Open("/dev/input/event0")

defer kbd.Close()

buf := make([]byte, 64)

        n, err := kbd.Read(buf)

//n, err := syscall.Read( int(kbd.Fd()), buf )

fmt.Println(n, err)

}

Which errs. The syscall gives: '-1 invalid argument'. However, the (I assume) corresponding C code works as expected...

#include <fcntl.h>

#include <stdio.h>

int main() {

int fd = open("/dev/input/event0", O_RDONLY);

char buf[64];

        read(fd, buf, sizeof(buf));

printf(buf);

close(fd);

}

 

So, what gives? I'm tempted to write this up as a bug, but this is my first time working with Go syscall, so I'm not confident that I'm not just being stupid. 

Running go1.2 linux/386. 

[Dave Cheney]

In both samples you have not checked the error from os.Open / open(2)

[Péter Szilágyi]

Expanding a bit on Dave's suggestions, adding the error check:

func main() {

kbd, err := os.Open("/dev/input/event0")

if err != nil {

panic(err)

}

defer kbd.Close()

buf := make([]byte, 64)

n, err := kbd.Read(buf)

//n, err := syscall.Read( int(kbd.Fd()), buf )

fmt.Println(n, err)

}

and running it now:

  $ go run main.go 

  panic: open /dev/input/event0: permission denied

  goroutine 1 [running]:

  runtime.panic(0x496940, 0xc21001e1b0)

          /opt/google/go/src/pkg/runtime/panic.c:266 +0xb6

  main.main()

          /work/iris/src/github.com/karalabe/test/main.go:11 +0x77

  exit status 2

whoops, /dev/input/event0 requires root permissions (on my Linux at least). Running with sudo:

  $ sudo go run main.go 

  48 <nil>

voila :)

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