ps(1): reuse keyword "cpu" to show CPU number

This flag will now show the processor number on which a process is running.

This change was inspired by PR129965. Initially I didn't think that the
patch attached to it was correct -- it sacrificed ki_estcpu use in "cpu"
for ki_lastcpu and I thought that the old functionality should be kept and
the new (cpu#) one added to it. But I've since discovered that ki_estcpu is
sched_4bsd-specific. What's worse, it represents the same thing as
ki_pctcpu, except ki_pctcpu is universal -- so "%cpu" has been using it
successfully. Therefore, I've decided to replace information based on
ki_estcpu with information based on ki_oncpu/ki_lastcpu.

Key parts of the code and manual changes were borrowed from top(1).

PR:		129965
Reported by:	Nikola Knežević
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D25377

bin/ps/extern.h

@@ -41,13 +41,14 @@ extern fixpt_t ccpu;
 extern int cflag, eval, fscale, nlistread, rawcpu;
 extern unsigned long mempages;
 extern time_t now;
-extern int showthreads, sumrusage, termwidth;
+extern int showthreads, sumrusage, termwidth, smp;
 extern STAILQ_HEAD(velisthead, varent) varlist;
 
 __BEGIN_DECLS
 char	 *arguments(KINFO *, VARENT *);
 char	 *command(KINFO *, VARENT *);
 char	 *cputime(KINFO *, VARENT *);
+char	 *cpunum(KINFO *, VARENT *);
 int	 donlist(void);
 char	 *elapsed(KINFO *, VARENT *);
 char	 *elapseds(KINFO *, VARENT *);

bin/ps/keyword.c

@@ -83,8 +83,7 @@ static VAR var[] = {
 	    CHAR, NULL, 0},
 	{"cow", "COW", NULL, "copy-on-write-faults", 0, kvar, KOFF(ki_cow),
 	    UINT, "u", 0},
-	{"cpu", "CPU", NULL, "cpu-usage", 0, kvar, KOFF(ki_estcpu), UINT, "d",
-	    0},
+	{"cpu", "C", NULL, "on-cpu", 0, cpunum, 0, CHAR, NULL, 0},
 	{"cputime", "", "time", NULL, 0, NULL, 0, CHAR, NULL, 0},
 	{"dsiz", "DSIZ", NULL, "data-size", 0, kvar, KOFF(ki_dsize), PGTOK,
 	    "ld", 0},

bin/ps/print.c

@@ -550,6 +550,22 @@ cputime(KINFO *k, VARENT *ve)
 	return (printtime(k, ve, secs, psecs));
 }
 
+char *
+cpunum(KINFO *k, VARENT *ve __unused)
+{
+	char *cpu;
+
+	if (!smp)
+		return (NULL);
+
+	if (k->ki_p->ki_stat == SRUN && k->ki_p->ki_oncpu != NOCPU) {
+		asprintf(&cpu, "%d", k->ki_p->ki_oncpu);
+	} else {
+		asprintf(&cpu, "%d", k->ki_p->ki_lastcpu);
+	}
+	return (cpu);
+}
+
 char *
 systime(KINFO *k, VARENT *ve)
 {

bin/ps/ps.1

@@ -29,7 +29,7 @@
 .\"     @(#)ps.1	8.3 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd October 31, 2018
+.Dd June 27, 2020
 .Dt PS 1
 .Os
 .Sh NAME
@@ -545,7 +545,8 @@ command and arguments
 .It Cm cow
 number of copy-on-write faults
 .It Cm cpu
-short-term CPU usage factor (for scheduling)
+The processor number on which the process is executing (visible only on SMP
+systems).
 .It Cm dsiz
 data size (in Kbytes)
 .It Cm emul

bin/ps/ps.c

@@ -105,6 +105,7 @@ int	 rawcpu;		/* -C */
 int	 sumrusage;		/* -S */
 int	 termwidth;		/* Width of the screen (0 == infinity). */
 int	 showthreads;		/* will threads be shown? */
+int	 smp;			/* multi-processor support */
 
 struct velisthead varlist = STAILQ_HEAD_INITIALIZER(varlist);
 
@@ -157,6 +158,7 @@ static void	 saveuser(KINFO *);
 static void	 scanvars(void);
 static void	 sizevars(void);
 static void	 pidmax_init(void);
+static void	 smp_init(void);
 static void	 usage(void);
 
 static char dfmt[] = "pid,tt,state,time,command";
@@ -226,6 +228,7 @@ main(int argc, char *argv[])
 		argv[1] = kludge_oldps_options(PS_ARGS, argv[1], argv[2]);
 
 	pidmax_init();
+	smp_init();
 
 	all = descendancy = _fmt = nselectors = optfatal = 0;
 	prtheader = showthreads = wflag = xkeep_implied = 0;
@@ -1456,6 +1459,18 @@ pidmax_init(void)
 	}
 }
 
+static void
+smp_init(void)
+{
+	size_t size;
+
+	size = sizeof(smp);
+	if ((sysctlbyname("machdep.smp_active", &smp, &size, NULL, 0) != 0 &&
+		sysctlbyname("kern.smp.active", &smp, &size, NULL, 0) != 0) ||
+		size != sizeof(smp))
+		smp = 0;
+}
+
 static void __dead2
 usage(void)
 {