x/sys/unix: unix.Klogctl does not allow access to len arg

[hugelgupf]

Linux sys_syslog looks like this:

int syslog(int type, char *buf, int len);

In Go's x/sys/unix, it's this

func Klogctl(typ int, buf []byte) (n int, err error)
// = syslog(typ, buf, len(buf))

That's kinda lame, because the len arg is not only used for the length, as you can see in the man page:

SYSLOG_ACTION_CONSOLE_LEVEL (8)
              The call sets console_loglevel to the value given in len,
              which must be an integer between 1 and 8 (inclusive).  The
              kernel silently enforces a minimum value of
              minimum_console_loglevel for len.  See the log level section
              for details.  The bufp argument is ignored.

So now you, either you gotta construct the unix.Syscall yourself or trick Klogctl into passing the right length:

unix.Klogctl(8, []byte{1, 2}) // Set console level 2!
// Yah ok this is silly

Perhaps there should be another function like this?

func Klogset(typ int, arg int) error
// = syslog(typ, nullptr, arg)

[hugelgupf]

Also, unix is missing const declarations for the typ argument:

const (                                                                                                                                                               
         SYSLOG_ACTION_READ_ALL      = 3                                                                                                                              
         SYSLOG_ACTION_READ_CLEAR    = 4                                                                                                                              
         SYSLOG_ACTION_CLEAR         = 5               
// etc                                                                                                               
         SYSLOG_ACTION_CONSOLE_LEVEL = 8                                                                                                                              
)   

[tklauser]

Adding Klogset (and the missing const declarations) as suggested sounds good to me. Want to send a CL?

[clickyotomy]

Hello! Is this up for grabs? I'd like to take it up, if that's OK.

[hugelgupf]

Do it!

[gopherbot]

Change https://golang.org/cl/199278 mentions this issue: x/sys/unix: Add Klogset and related SYSLOG_ACTION_ constants