libc: re-implement getuser() by stating /proc/$pid/status

The idea is to avoid the magic files that contain
per process information in devcons when possible.
It will make it easier to deprecate them in the future.

sys/src/libc/9sys/getuser.c

@@ -0,0 +1,17 @@
+#include <u.h>
+#include <libc.h>
+
+char *
+getuser(void)
+{
+	static char user[64];
+	char name[32];
+	Dir *dir;
+
+	snprint(name, sizeof(name), "/proc/%lud/status", (ulong)getpid());
+	if((dir = dirstat(name)) == nil)
+		return "none";
+	snprint(user, sizeof(user), "%s", dir->uid);
+	free(dir);
+	return user;
+}

sys/src/libc/9sys/mkfile

@@ -24,6 +24,7 @@ OFILES=\
 	getenv.$O\
 	getpid.$O\
 	getppid.$O\
+	getuser.$O\
 	getwd.$O\
 	idn.$O\
 	iounit.$O\

sys/src/libc/port/getuser.c

@@ -1,21 +0,0 @@
-#include <u.h>
-#include <libc.h>
-
-char *
-getuser(void)
-{
-	static char user[64];
-	int fd;
-	int n;
-
-	fd = open("/dev/user", OREAD|OCEXEC);
-	if(fd < 0)
-		return "none";
-	n = read(fd, user, (sizeof user)-1);
-	close(fd);
-	if(n <= 0)
-		strcpy(user, "none");
-	else
-		user[n] = 0;
-	return user;
-}

sys/src/libc/port/mkfile

@@ -32,7 +32,6 @@ CFILES=\
 	frexp.c\
 	getcallerpc.c\
 	getfields.c\
-	getuser.c\
 	hangup.c\
 	hypot.c\
 	lnrand.c\