kernel & libbsd.so: add getloadavg() and _user_get_loadavg()

the algorithm and reference values are from FreeBSD.

Change-Id: Ia74a796e13adce6a70434c7546c25ca3d553f11f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9150
Reviewed-by: waddlesplash <[email protected]>
Reviewed-by: Jérôme Duval <[email protected]>
Tested-by: Commit checker robot <[email protected]>

headers/compatibility/bsd/stdlib.h

@@ -30,6 +30,8 @@ int			mkstemps(char *templat, int slen);
 long long	strtonum(const char *numstr, long long minval,
 				long long maxval, const char **errstrp);
 
+int			getloadavg(double array[], int size);
+
 #ifdef __cplusplus
 }
 #endif

headers/private/kernel/kscheduler.h

@@ -85,6 +85,7 @@ void scheduler_add_listener(struct SchedulerListener* listener);
 void scheduler_remove_listener(struct SchedulerListener* listener);
 
 void scheduler_init(void);
+status_t scheduler_loadavg_init();
 void scheduler_enable_scheduling(void);
 void scheduler_update_policy(void);
 
@@ -95,6 +96,9 @@ status_t _user_analyze_scheduling(bigtime_t from, bigtime_t until, void* buffer,
 status_t _user_set_scheduler_mode(int32 mode);
 int32 _user_get_scheduler_mode(void);
 
+status_t _user_get_loadavg(struct loadavg* info, size_t size);
+
+
 #ifdef __cplusplus
 }
 #endif

headers/private/system/scheduler_defs.h

@@ -62,4 +62,10 @@ struct scheduling_analysis {
 };
 
 
+struct loadavg {
+	uint32	ldavg[3];
+	long 	fscale;
+};
+
+
 #endif	/* _SYSTEM_SCHEDULER_DEFS_H */

headers/private/system/syscalls.h

@@ -28,6 +28,7 @@ struct fd_info;
 struct fd_set;
 struct fs_info;
 struct iovec;
+struct loadavg;
 struct msqid_ds;
 struct net_stat;
 struct pollfd;
@@ -212,6 +213,7 @@ extern bigtime_t	_kern_estimate_max_scheduling_latency(thread_id thread);
 
 extern status_t		_kern_set_scheduler_mode(int32 mode);
 extern int32		_kern_get_scheduler_mode(void);
+extern status_t		_kern_get_loadavg(struct loadavg* info, size_t size);
 
 // user/group functions
 extern gid_t		_kern_getgid(bool effective);