libc: implement getppid() reading /proc/$pid/ppid instead of /dev/ppid

The devcons driver is really the wrong place to
serve per process information.

sys/man/2/getpid

@@ -13,27 +13,18 @@ int getpid(void)
 int getppid(void)
 .SH DESCRIPTION
 .I Getpid
-reads
-.B /dev/pid
-(see
-.IR cons (3))
-and converts it to get the process id of the current process,
+returns the process id of the current process,
 a number guaranteed to be unique among all running processes on the machine
 executing
 .IR getpid .
 .PP
 .I Getppid
-reads
-.B /dev/ppid
-(see
-.IR cons (3))
-and converts it to get the id of the parent of the current process.
+returns the process id of the parent of the current process.
 .SH SOURCE
 .B /sys/src/libc/9sys
 .SH SEE ALSO
 .IR intro (2),
 .IR exec (2),
-.IR cons (3),
 .IR proc (3)
 .SH DIAGNOSTICS
 Returns 0 and

sys/src/ape/lib/ap/plan9/getppid.c

@@ -1,6 +1,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
@@ -9,14 +10,15 @@
 pid_t
 getppid(void)
 {
-	char b[20];
+	char buf[32];
 	int f;
 
-	memset(b, 0, sizeof(b));
-	f = _OPEN("/dev/ppid", OREAD);
-	if(f >= 0) {
-		_PREAD(f, b, sizeof(b), 0);
-		_CLOSE(f);
-	}
-	return atol(b);
+	snprintf(buf, sizeof(buf), "/proc/%d/ppid", getpid());
+	f = open(buf, 0);
+	if(f < 0)
+		return 0;
+	memset(buf, 0, sizeof(buf));
+	read(f, buf, sizeof(buf)-1);
+	close(f);
+	return atol(buf);
 }

sys/src/libc/9sys/getppid.c

@@ -4,14 +4,15 @@
 int
 getppid(void)
 {
-	char b[20];
+	char buf[32];
 	int f;
 
-	memset(b, 0, sizeof(b));
-	f = open("/dev/ppid", OREAD|OCEXEC);
-	if(f >= 0) {
-		read(f, b, sizeof(b));
-		close(f);
-	}
-	return atol(b);
+	snprint(buf, sizeof(buf), "/proc/%lud/ppid", (ulong)getpid());
+	f = open(buf, OREAD|OCEXEC);
+	if(f < 0)
+		return 0;
+	memset(buf, 0, sizeof(buf));
+	read(f, buf, sizeof(buf)-1);
+	close(f);
+	return atol(buf);
 }