From de11e11f9bd0294c5f0f306843f4aa16da54c228 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Tue, 24 Feb 1998 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1998-02-24

---
 port/chan.c    | 64 +++++++++++++++++++++-----------------------------
 port/portfns.h |  2 +-
 port/sysfile.c |  6 +++--
 3 files changed, 32 insertions(+), 40 deletions(-)

diff --git a/port/chan.c b/port/chan.c
index 16e45e1df1182997cdd09e980c0d7c3e02d77c05..2b80158772f363ba522081d0fd1b619d93bf7bd8 100644
--- a/port/chan.c
+++ b/port/chan.c
@@ -378,36 +378,38 @@ undomount(Chan *c)
 	return c;
 }
 
-Chan*
-walk(Chan *ac, char *name, int domnt)
+int
+walk(Chan **cp, char *name, int domnt)
 {
 	Pgrp *pg;
-	Chan *c;
+	Chan *c, *ac;
 	Mount *f;
 	int dotdot;
 
+	ac = *cp;
+
 	if(name[0] == '\0')
-		return ac;
+		return 0;
 
 	dotdot = 0;
 	if(name[0] == '.' && name[1] == '.' && name[2] == '\0') {
-		ac = undomount(ac);
+		*cp = ac = undomount(ac);
 		dotdot = 1;
 	}
 
 	ac->flag &= ~CCREATE;	/* not inherited through a walk */
 	if(devtab[ac->type]->walk(ac, name) != 0) {
 		if(dotdot)
-			ac = undomount(ac);
+			*cp = undomount(*cp);
 		if(domnt)
-			ac = domount(ac);
-		return ac;
+			*cp = domount(*cp);
+		return 0;
 	}
 
-	if(ac->mnt == 0) 
-		return 0;
+	if(ac->mnt == nil) 
+		return -1;
 
-	c = 0;
+	c = nil;
 	pg = up->pgrp;
 
 	rlock(&pg->ns);
@@ -423,13 +425,13 @@ walk(Chan *ac, char *name, int domnt)
 		if(devtab[c->type]->walk(c, name) != 0)
 			break;
 		cclose(c);
-		c = 0;
+		c = nil;
 	}
 	poperror();
 	runlock(&pg->ns);
 
-	if(c == 0)
-		return 0;
+	if(c == nil)
+		return -1;
 
 	if(dotdot)
 		c = undomount(c);
@@ -444,7 +446,8 @@ walk(Chan *ac, char *name, int domnt)
 		poperror();
 	}
 	cclose(ac);
-	return c;	
+	*cp = c;
+	return 0;	
 }
 
 /*
@@ -537,7 +540,7 @@ namec(char *name, int amode, int omode, ulong perm)
 	char *elem;
 	int t, n;
 	int mntok, isdot;
-	Chan *c, *nc, *cc;
+	Chan *c, *cc;
 	char createerr[ERRLEN];
 
 	if(name[0] == 0)
@@ -611,10 +614,8 @@ namec(char *name, int amode, int omode, ulong perm)
 		c = domount(c);			/* see case Atodir below */
 
 	while(*name) {
-		nc = walk(c, elem, mntok);
-		if(nc == 0)
+		if(walk(&c, elem, mntok) < 0)
 			error(Enonexist);
-		c = nc;
 		name = nextelem(name, elem);
 	}
 
@@ -624,10 +625,8 @@ namec(char *name, int amode, int omode, ulong perm)
 			c = domount(c);
 			break;
 		}
-		nc = walk(c, elem, mntok);
-		if(nc == 0)
+		if(walk(&c, elem, mntok) < 0)
 			error(Enonexist);
-		c = nc;
 		break;
 
 	case Atodir:
@@ -635,10 +634,8 @@ namec(char *name, int amode, int omode, ulong perm)
 		 * Directories (e.g. for cd) are left before the mount point,
 		 * so one may mount on / or . and see the effect.
 		 */
-		nc = walk(c, elem, 0);
-		if(nc == 0)
+		if(walk(&c, elem, 0) < 0)
 			error(Enonexist);
-		c = nc;
 		if(!(c->qid.path & CHDIR))
 			error(Enotdir);
 		break;
@@ -647,10 +644,8 @@ namec(char *name, int amode, int omode, ulong perm)
 		if(isdot)
 			c = domount(c);
 		else {
-			nc = walk(c, elem, mntok);
-			if(nc == 0)
+			if(walk(&c, elem, mntok) < 0)
 				error(Enonexist);
-			c = nc;
 		}
 	Open:
 		/* else error() in open has wrong value of c saved */
@@ -673,10 +668,8 @@ namec(char *name, int amode, int omode, ulong perm)
 		 * one wants subsequent mounts to be attached to the 
 		 * original directory, not the replacement.
 		 */
-		nc = walk(c, elem, 0);
-		if(nc == 0)
+		if(walk(&c, elem, 0) < 0)
 			error(Enonexist);
-		c = nc;
 		break;
 
 	case Acreate:
@@ -695,11 +688,10 @@ namec(char *name, int amode, int omode, ulong perm)
 			nexterror();
 		}
 		nameok(elem);
-		nc = walk(cc, elem, 1);
-		if(nc != 0) {
+		if(walk(&cc, elem, 1) == 0){
 			poperror();
 			cclose(c);
-			c = nc;
+			c = cc;
 			omode |= OTRUNC;
 			goto Open;
 		}
@@ -718,10 +710,8 @@ namec(char *name, int amode, int omode, ulong perm)
 		 */
 		if(waserror()) {
 			strcpy(createerr, up->error);
-			nc = walk(c, elem, 1);
-			if(nc == 0)
+			if(walk(&c, elem, 1) < 0)
 				error(createerr);
-			c = nc;
 			omode |= OTRUNC;
 			goto Open;
 		}
diff --git a/port/portfns.h b/port/portfns.h
index 7b5eb6379e8fc73f413feec934a60571128e7d22..69b603ea5b4a3318af670f955092c7f68e95b199 100644
--- a/port/portfns.h
+++ b/port/portfns.h
@@ -297,7 +297,7 @@ void		validaddr(ulong, ulong, int);
 void		vcacheinval(Page*, ulong);
 void*		vmemchr(void*, int, int);
 int		wakeup(Rendez*);
-Chan*		walk(Chan*, char*, int);
+int		walk(Chan**, char*, int);
 void		wlock(RWlock*);
 void		wunlock(RWlock*);
 #define		xalloc(s)	xallocz(s, 1)
diff --git a/port/sysfile.c b/port/sysfile.c
index afdd8f1ea4aeddc39c0873a5b6aa5f35798501cc..010020be50e25b19f9e14f34699d07642fd62441 100644
--- a/port/sysfile.c
+++ b/port/sysfile.c
@@ -166,8 +166,10 @@ syspipe(ulong *arg)
 		nexterror();
 	}
 	c[1] = cclone(c[0], 0);
-	walk(c[0], "data", 1);
-	walk(c[1], "data1", 1);
+	if(walk(&c[0], "data", 1) < 0)
+		error(Egreg);
+	if(walk(&c[1], "data1", 1) < 0)
+		error(Egreg);
 	c[0] = d->open(c[0], ORDWR);
 	c[1] = d->open(c[1], ORDWR);
 	fd[0] = newfd(c[0]);