BSD platforms: Reject negative and zero KERN_FSCALE factors

The "fscale" value, retrieved by sysctl() in BSD platforms, is used for
computing CPU percentages of the processes. To prevent a division by
zero, we should reject a zero "fscale" value. (A negative "fscale"
value will not make sense either.)

For DragonFlyBSD and FreeBSD, this would fall back to the hard-coded
default scale.
For NetBSD and OpenBSD, there is no hard-coded default value, so the
zero or negative "fscale" is now a fatal error.

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

dragonflybsd/DragonFlyBSDMachine.c

@@ -105,7 +105,7 @@ Machine* Machine_new(UsersTable* usersTable, uid_t userId) {
    }
 
    len = sizeof(this->kernelFScale);
-   if (sysctlbyname("kern.fscale", &this->kernelFScale, &len, NULL, 0) == -1) {
+   if (sysctlbyname("kern.fscale", &this->kernelFScale, &len, NULL, 0) == -1 || this->kernelFScale <= 0) {
       //sane default for kernel provided CPU percentage scaling, at least on x86 machines, in case this sysctl call failed
       this->kernelFScale = 2048;
    }

freebsd/FreeBSDMachine.c

@@ -136,7 +136,7 @@ Machine* Machine_new(UsersTable* usersTable, uid_t userId) {
    }
 
    len = sizeof(this->kernelFScale);
-   if (sysctlbyname("kern.fscale", &this->kernelFScale, &len, NULL, 0) == -1) {
+   if (sysctlbyname("kern.fscale", &this->kernelFScale, &len, NULL, 0) == -1 || this->kernelFScale <= 0) {
       //sane default for kernel provided CPU percentage scaling, at least on x86 machines, in case this sysctl call failed
       this->kernelFScale = 2048;
    }

netbsd/NetBSDMachine.c

@@ -112,7 +112,7 @@ Machine* Machine_new(UsersTable* usersTable, uid_t userId) {
    NetBSDMachine_updateCPUcount(this);
 
    size = sizeof(this->fscale);
-   if (sysctl(fmib, 2, &this->fscale, &size, NULL, 0) < 0) {
+   if (sysctl(fmib, 2, &this->fscale, &size, NULL, 0) < 0 || this->fscale <= 0) {
       CRT_fatalError("fscale sysctl call failed");
    }
 

openbsd/OpenBSDMachine.c

@@ -99,7 +99,7 @@ Machine* Machine_new(UsersTable* usersTable, uid_t userId) {
    OpenBSDProcessList_updateCPUcount(this);
 
    size = sizeof(this->fscale);
-   if (sysctl(fmib, 2, &this->fscale, &size, NULL, 0) < 0) {
+   if (sysctl(fmib, 2, &this->fscale, &size, NULL, 0) < 0 || this->fscale <= 0) {
       CRT_fatalError("fscale sysctl call failed");
    }