dashboard: CPU, memory, diskIO and traffic on the footer (#15950)

* dashboard: footer, deep state update

* dashboard: resolve asset path

* dashboard: prevent state update on every reconnection

* dashboard: fix linter issue

* dashboard, cmd: minor UI fix, include commit hash

* dashboard: gitCommit renamed to commit

* dashboard: move the geth version to the right, make commit optional

* dashboard: memory, traffic and CPU on footer

* dashboard: fix merge

* dashboard: CPU, diskIO on footer

* dashboard: rename variables, use group declaration

* dashboard: docs

vendor/github.com/elastic/gosigar/sigar_freebsd.go

@@ -0,0 +1,108 @@
+// Copied and modified from sigar_linux.go.
+
+package gosigar
+
+import (
+	"io/ioutil"
+	"strconv"
+	"strings"
+	"unsafe"
+)
+
+/*
+#include <sys/param.h>
+#include <sys/mount.h>
+#include <sys/ucred.h>
+#include <sys/types.h>
+#include <sys/sysctl.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <time.h>
+*/
+import "C"
+
+func init() {
+	system.ticks = uint64(C.sysconf(C._SC_CLK_TCK))
+
+	Procd = "/compat/linux/proc"
+
+	getLinuxBootTime()
+}
+
+func getMountTableFileName() string {
+	return Procd + "/mtab"
+}
+
+func (self *Uptime) Get() error {
+	ts := C.struct_timespec{}
+
+	if _, err := C.clock_gettime(C.CLOCK_UPTIME, &ts); err != nil {
+		return err
+	}
+
+	self.Length = float64(ts.tv_sec) + 1e-9*float64(ts.tv_nsec)
+
+	return nil
+}
+
+func (self *FDUsage) Get() error {
+	val := C.uint32_t(0)
+	sc := C.size_t(4)
+
+	name := C.CString("kern.openfiles")
+	_, err := C.sysctlbyname(name, unsafe.Pointer(&val), &sc, nil, 0)
+	C.free(unsafe.Pointer(name))
+	if err != nil {
+		return err
+	}
+	self.Open = uint64(val)
+
+	name = C.CString("kern.maxfiles")
+	_, err = C.sysctlbyname(name, unsafe.Pointer(&val), &sc, nil, 0)
+	C.free(unsafe.Pointer(name))
+	if err != nil {
+		return err
+	}
+	self.Max = uint64(val)
+
+	self.Unused = self.Max - self.Open
+
+	return nil
+}
+
+func (self *ProcFDUsage) Get(pid int) error {
+	err := readFile("/proc/"+strconv.Itoa(pid)+"/rlimit", func(line string) bool {
+		if strings.HasPrefix(line, "nofile") {
+			fields := strings.Fields(line)
+			if len(fields) == 3 {
+				self.SoftLimit, _ = strconv.ParseUint(fields[1], 10, 64)
+				self.HardLimit, _ = strconv.ParseUint(fields[2], 10, 64)
+			}
+			return false
+		}
+		return true
+	})
+	if err != nil {
+		return err
+	}
+
+	// linprocfs only provides this information for this process (self).
+	fds, err := ioutil.ReadDir(procFileName(pid, "fd"))
+	if err != nil {
+		return err
+	}
+	self.Open = uint64(len(fds))
+
+	return nil
+}
+
+func parseCpuStat(self *Cpu, line string) error {
+	fields := strings.Fields(line)
+
+	self.User, _ = strtoull(fields[1])
+	self.Nice, _ = strtoull(fields[2])
+	self.Sys, _ = strtoull(fields[3])
+	self.Idle, _ = strtoull(fields[4])
+	return nil
+}