kernel: pgrpcpy(), simplify Mount structure

instead of ordering the source mount list, order the new destination
list which has the advantage that we do not need to wlock the source
namespace, so copying can be done in parallel and we do not need the
copy forward pointer in the Mount structure.

the Mhead back pointer in the Mount strcture was unused, removed.

5 files changed, 19 insertions, 17 deletions

diff --git a/sys/src/9/port/chan.c b/sys/src/9/port/chan.c
index 41b686170..7e87b9110 100644
--- a/sys/src/9/port/chan.c
+++ b/sys/src/9/port/chan.c
@@ -704,7 +704,7 @@ cmount(Chan **newp, Chan *old, int flag, char *spec)
 		 *  node to the mount chain.
 		 */
 		if(order != MREPL)
-			m->mount = newmount(m, old, 0, 0);
+			m->mount = newmount(old, 0, nil);
 	}
 	wlock(&m->lock);
 	if(waserror()){
@@ -713,7 +713,7 @@ cmount(Chan **newp, Chan *old, int flag, char *spec)
 	}
 	wunlock(&pg->ns);
 
-	nm = newmount(m, new, flag, spec);
+	nm = newmount(new, flag, spec);
 	if(mh != nil && mh->mount != nil){
 		/*
 		 *  copy a union when binding it onto a directory
@@ -724,7 +724,7 @@ cmount(Chan **newp, Chan *old, int flag, char *spec)
 		h = &nm->next;
 		um = mh->mount;
 		for(um = um->next; um != nil; um = um->next){
-			f = newmount(m, um->to, flg, um->spec);
+			f = newmount(um->to, flg, um->spec);
 			*h = f;
 			h = &f->next;
 		}
diff --git a/sys/src/9/port/devshr.c b/sys/src/9/port/devshr.c
index 03a79bc8a..bc7677210 100644
--- a/sys/src/9/port/devshr.c
+++ b/sys/src/9/port/devshr.c
@@ -531,7 +531,6 @@ shrcreate(Chan *c, char *name, int omode, ulong perm)
 
 		incref(mpt);
 		mpt->m.mflag = (h->mount == nil) ? MCREATE : 0;
-		mpt->m.head = h;
 		mpt->m.next = h->mount;
 		h->mount = &mpt->m;
 
@@ -602,7 +601,6 @@ shrremove(Chan *c)
 			if(*ml == m){
 				*ml = m->next;
 				m->next = nil;
-				m->head = nil;
 				putmpt(mpt);
 				break;
 			}
diff --git a/sys/src/9/port/pgrp.c b/sys/src/9/port/pgrp.c
index 430052db9..5de7c695f 100644
--- a/sys/src/9/port/pgrp.c
+++ b/sys/src/9/port/pgrp.c
@@ -115,11 +115,12 @@ pgrpinsert(Mount **order, Mount *m)
 void
 pgrpcpy(Pgrp *to, Pgrp *from)
 {
-	int i;
 	Mount *n, *m, **link, *order;
 	Mhead *f, **tom, **l, *mh;
+	int i;
 
-	wlock(&from->ns);
+	wlock(&to->ns);
+	rlock(&from->ns);
 	order = nil;
 	tom = to->mnthash;
 	for(i = 0; i < MNTHASH; i++) {
@@ -131,9 +132,14 @@ pgrpcpy(Pgrp *to, Pgrp *from)
 			l = &mh->hash;
 			link = &mh->mount;
 			for(m = f->mount; m != nil; m = m->next) {
-				n = newmount(mh, m->to, m->mflag, m->spec);
-				m->copy = n;
-				pgrpinsert(&order, m);
+				n = smalloc(sizeof(Mount));
+				n->mountid = m->mountid;
+				n->mflag = m->mflag;
+				n->to = m->to;
+				incref(n->to);
+				if(m->spec != nil)
+					kstrdup(&n->spec, m->spec);
+				pgrpinsert(&order, n);
 				*link = n;
 				link = &n->next;
 			}
@@ -144,8 +150,9 @@ pgrpcpy(Pgrp *to, Pgrp *from)
 	 * Allocate mount ids in the same sequence as the parent group
 	 */
 	for(m = order; m != nil; m = m->order)
-		m->copy->mountid = incref(&mountid);
-	wunlock(&from->ns);
+		m->mountid = incref(&mountid);
+	runlock(&from->ns);
+	wunlock(&to->ns);
 }
 
 Fgrp*
@@ -246,12 +253,11 @@ forceclosefgrp(void)
 
 
 Mount*
-newmount(Mhead *mh, Chan *to, int flag, char *spec)
+newmount(Chan *to, int flag, char *spec)
 {
 	Mount *m;
 
 	m = smalloc(sizeof(Mount));
-	m->head = mh;
 	m->to = to;
 	incref(to);
 	m->mountid = incref(&mountid);
diff --git a/sys/src/9/port/portdat.h b/sys/src/9/port/portdat.h
index 9eafd7b93..21107d870 100644
--- a/sys/src/9/port/portdat.h
+++ b/sys/src/9/port/portdat.h
@@ -255,8 +255,6 @@ struct Mount
 {
 	ulong	mountid;
 	Mount*	next;
-	Mhead*	head;
-	Mount*	copy;
 	Mount*	order;
 	Chan*	to;			/* channel replacing channel */
 	int	mflag;
diff --git a/sys/src/9/port/portfns.h b/sys/src/9/port/portfns.h
index 6ca7a54ba..4944b9285 100644
--- a/sys/src/9/port/portfns.h
+++ b/sys/src/9/port/portfns.h
@@ -190,7 +190,7 @@ int		needpages(void*);
 Chan*		newchan(void);
 int		newfd(Chan*);
 Mhead*		newmhead(Chan*);
-Mount*		newmount(Mhead*, Chan*, int, char*);
+Mount*		newmount(Chan*, int, char*);
 Page*		newpage(int, Segment **, uintptr);
 Path*		newpath(char*);
 Pgrp*		newpgrp(void);