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Date: Wed, 13 Aug 2014 20:29:21 +0200
From: Lars Engels <lme@freebsd.org>
To: "Sam Fourman Jr." <sfourman@gmail.com>
Subject: Re: sysctl(3) question
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On Wed, Aug 13, 2014 at 12:00:32PM -0500, Sam Fourman Jr. wrote:
> Hello Hackers,
>=20
> the following command gives me the disks in a system
> sysctl kern.disks
> kern.disks: cd0 ada0
>=20
>=20
> my question is, what paramaters and values do I have to pass sysctl(3) to
> give me those disks?
>=20
>=20
>=20
> I have tried and I cant get HW_DISKNAMES from <sys/sysctl.h> to work
>=20
>=20
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/param.h>
> #include <sys/sysctl.h>
> #include <err.h>
>=20
> int main(void) {
>=20
> int mib[2];
> size_t len;
> char *p;
>=20
> mib[0] =3D CTL_HW;
> mib[1] =3D HW_DISKNAMES;
>=20
>         /* Determine how much space to allocate. */
>         if (sysctl(mib, 2, NULL, &len, NULL, 0) =3D=3D -1)
>         err(1, "sysctl");
>=20
>         if ((p =3D (char *)malloc(len)) =3D=3D NULL)
>         err(1, NULL);
>=20
>         /* Populate the allocated area with the string returned
>         *        * by sysctl.
>         *                */
>         if (sysctl(mib, 2, p, &len, NULL, 0) =3D=3D -1)
>         err(1, "sysctl");
>=20
> printf("%s\n", p);
>=20
> return 0;
> }

Try sysctlbyname():

#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <err.h>

int main(void) {

size_t len;
char *p;

/* Determine how much space to allocate. */
if (sysctlbyname("kern.disks", NULL, &len, NULL, 0) =3D=3D -1)
err(1, "sysctl");

if ((p =3D (char *)malloc(len)) =3D=3D NULL)
err(1, NULL);

if (sysctlbyname("kern.disks", p, &len, NULL, 0) =3D=3D -1)
	err(1, "sysctl");

printf("%s\n", p);

return 0;
}


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