kernel: fix #0/brk/ qid (it's a special directory, not a special file)

qa/kern/brk.c

@@ -23,7 +23,7 @@ main(void)
 {
 	long b, b1;
 
-	b = create("#0/brk", -1, 16*1024*1024);
+	b = create("#0/brk/set", -1, 16*1024*1024);
 	if(b >= 0){
 		print("FAIL: create returned fd %d.\n", b);
 		exits("FAIL");

sys/src/kern/port/devself.c

@@ -63,7 +63,7 @@ Cmdtab proccmd[] = {
 
 static Dirtab selfdir[]={
 	".",		{Qdir, 0, QTDIR},	0,		DMDIR|0777,
-	"brk",		{Qbrk},			0,		0,
+	"brk",		{Qbrk, 0, QTDIR},	0,		DMDIR|0300,
 	"pid",		{Qpid},			0,		0400,
 	"ppid",		{Qppid},		0,		0400,
 	"pgrpid",	{Qpgrpid},		0,		0400,
@@ -197,6 +197,8 @@ selfcreate(Chan* c, char* name, unsigned long omode, unsigned long perm)
 	default:
 		error(Eperm);
 	case Qbrk:
+		if(strcmp(name, "set") != 0)
+			error(Eperm);
 		e = (long)grow_bss(perm);
 		errorl(nil, ~e);
 	}

sys/src/lib/c/9sys/sbrk.c

@@ -18,7 +18,7 @@ enum
 	Round	= 7
 };
 
-#define brk_(p) ((uintptr_t)~create("#0/brk", -1, p))
+#define brk_(p) ((uintptr_t)~create("#0/brk/set", -1, p))
 
 int
 brk(void *p)