sysctlbyname() On FreeBSD

[Carpetsmoker]

I recently bought a Thinkpad T61 (Didn't go for the Dell Vermaden), but all battery indicators I could find for FreeBSD eiter do not work, or don't work as I want them to, creating a simple tray application is simple, but I'm having problems with getting the sysctl.

From the commandline:
% sysctl hw.acpi.battery.life
hw.acpi.battery.life: 99

99% means its full, so now from python, from an example found here:

def CheckBatt(tray):
        libc = ctypes.CDLL('libc.so')
        size = ctypes.c_uint(0)
        #libc.sysctlbyname("hw.acpi.battery.life", None, ctypes.byref(size), None, 0) 
        buf = ctypes.create_string_buffer(size.value)
        libc.sysctlbyname("hw.acpi.battery.life", buf, ctypes.byref(size), None, 0)

        print buf.value
        return True

output: `c'

Hm, maybe something went wrong with ctypes? Lets try from C:

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int
main()
{
        size_t size;
        int buf;
        size = sizeof buf;

        sysctlbyname("hw.acpi.battery.life", &buf, &size, NULL, 0);

        printf("`%s'\n", &buf);
        return 0;
}

Output: `c' ... So the problem isn't in ctypes, but probably in my use of sysctlbyname() (?)

I am not an experienced C programmer, I usually stick to stuff like python, I'm probably doing something stupid, but I can't figure out what.

Also, why does the python example linked above use two sysctlbyname() calls? It seems redundant to me...

[anemos]

I think you have to write

printf("`%d'\n", buf);

instead of

printf("`%s'\n", &buf);

[ephemera]

try:

        if (sysctlbyname("hw.acpi.battery.life", &buf, &size, NULL, 0) < 0) {
             perror("sysctl"); 
             exit(1); 
       }

        printf("`%d'\n", buf);

[Carpetsmoker]

No error, sysctlbyname() returns 0 as it should.

[BSDfan666]

What about the following?

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int main(void) {
	int mib[4];
	size_t len;
	char buf[BUFSIZ];
	int buflen = BUFSIZ;

	len = sizeof(mib);

	if(sysctlnametomib("hw.acpi.battery.life", mib, &len) == -1) {
		return 1;
	}

	if(sysctl(mib, len, buf, &buflen, NULL, 0) == -1) {
		return 1;
	}
	
	printf("%s\n", buf);
}

I can't confirm it'll compile, OpenBSD lacks this function..

[BSDfan666]

Let's try that again...

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int main(void) {
	int mib[4], life;
	size_t miblen, lifelen;

	miblen = sizeof(mib);
	lifelen = sizeof(life);

	if(sysctlnametomib("hw.acpi.battery.life", mib, &miblen) == -1) {
		return 1;
	}

	if(sysctl(mib, miblen, &life, &lifelen, NULL, 0) == -1) {
		return 1;
	}
	
	printf("%d\n", life);
	
	return 0;
}

Hope it helps..

[BSDfan666]

The following, from your original post.. should work.

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int
main()
{
        size_t size;
        int buf;
        size = sizeof buf;

        sysctlbyname("hw.acpi.battery.life", &buf, &size, NULL, 0);

        printf("%d\n", buf);
        return 0;
}

Take care pal.

EDIT: Fixed the above code, should work now.

[Carpetsmoker]

Ok, the problem with the C example was the wrong printf() statement, as anemos pointed out.

The problem with the python example was that I used the wrong type for buf, string instead of int.

For those interested, a working python example:

import ctypes

libc = ctypes.CDLL('libc.so')
size = ctypes.c_size_t()
buf = ctypes.c_int()
size.value = ctypes.sizeof(buf)
libc.sysctlbyname("hw.acpi.battery.life", ctypes.byref(buf), ctypes.byref(size), None, 0)

print buf.value

However, BSDFan666 pointed out over jabber that the apm(8) command is a more convenient and portable way of getting the same information ... Thanks!

[roddierod]

Python you could have done:

import commands

def CheckBattery():
  return commands.getstatusoutput("sysctl hw.acpi.battery.life")[1].split(:)[1]

[TerryP]

If you're going to play with external applications: you should use the subprocess module, not commands. I believe the getstatusoutput() function was also moved to subprocess in py26, and commands is kaput in py30; in favor of subprocess.

[roddierod]

For more complex external commands I usually do, but I just thought subprocess was overkill for this.

Didn't know commands was gone in 3 thought, thanks.

[Carpetsmoker]

@roddierod
That's what I did, but using ctypes would be a better since it doesn't spawn a shell.