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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.

--- a/sys/man/2/getuser

+++ b/sys/man/2/getuser

@@ -18,13 +18,13 @@

 name of the user who

 owns the current process.

 .I Getuser

-reads

-.B /dev/user

+stats the file

+.BI /proc/ pid /status

 to find the name.

 .PP

 .I Sysname

-provides the same service for the file

-.BR #c/sysname ,

+reads the file

+.BR /dev/sysname ,

 which contains the name of the machine.

 Unlike

 .IR getuser ,

@@ -31,9 +31,10 @@

 .I sysname

 caches the string, reading the file only once.

 .SH SOURCE

-.B /sys/src/libc/port/getuser.c

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

 .br

 .B /sys/src/libc/9sys/sysname.c 

 .SH SEE ALSO

 .IR intro (2),

+.IR proc (3),

 .IR cons (3)

--- /dev/null

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

@@ -1,0 +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;

+}

--- a/sys/src/libc/9sys/mkfile

+++ b/sys/src/libc/9sys/mkfile

@@ -24,6 +24,7 @@

 	getenv.$O\

 	getpid.$O\

 	getppid.$O\

+	getuser.$O\

 	getwd.$O\

 	idn.$O\

 	iounit.$O\

--- a/sys/src/libc/port/getuser.c

+++ /dev/null

@@ -1,21 +1,0 @@

-#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;

-}

--- a/sys/src/libc/port/mkfile

+++ b/sys/src/libc/port/mkfile

@@ -32,7 +32,6 @@

 	frexp.c\

 	getcallerpc.c\

 	getfields.c\

-	getuser.c\

 	hangup.c\

 	hypot.c\

 	lnrand.c\