From fb4aaf15cbc6be3c73be37863a2ea62bee43f4b9 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Thu, 11 Apr 1991 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1991-04-11

---
 gnot/dat.h        |  8 ++++---
 gnot/devcons.c    | 40 +++++++++++++++++------------------
 gnot/devincon.c   |  4 ++--
 gnot/devport.c    | 12 +++++------
 gnot/fns.h        |  2 +-
 gnot/main.c       |  6 +++---
 gnot/mem.h        |  3 +++
 port/dev.c        |  6 ++++++
 port/devbit.c     |  8 +++----
 port/devboot.c    | 14 ++++++------
 port/devcons.c    | 36 +++++++++++++++----------------
 port/devdk.c      | 10 ++++-----
 port/devdup.c     |  4 ++--
 port/devenv.c     | 18 ++++++++--------
 port/deviproute.c | 10 ++++-----
 port/devkprof.c   | 12 +++++------
 port/devlance.c   | 22 +++++++++----------
 port/devmnt.c     | 21 +++++++++---------
 port/devnonet.c   | 12 +++++------
 port/devpipe.c    |  4 ++--
 port/devproc.c    | 54 +++++++++++++++++++++++------------------------
 port/devroot.c    | 20 +++++++++---------
 port/devscsi.c    | 12 +++++------
 port/devsrv.c     |  6 ++----
 port/devwren.c    | 14 ++++++------
 port/fault.c      |  9 ++++----
 port/stream.c     | 32 +++++++++++++++++++++-------
 port/sysfile.c    | 27 +++++++++++++-----------
 port/sysproc.c    |  2 +-
 power/dat.h       |  8 ++++---
 power/devbit3.c   |  4 ++--
 power/devhotrod.c |  4 ++--
 power/devhs.c     |  4 ++--
 power/devrtc.c    |  8 +++----
 power/fns.h       |  2 +-
 ss/dat.h          |  5 +++--
 ss/mem.h          |  2 +-
 37 files changed, 247 insertions(+), 218 deletions(-)

diff --git a/gnot/dat.h b/gnot/dat.h
index 975ce3a30a06f39bd27764eb952d1bbbd40f9231..7c7ffd1485873ffde31fbb3d809e9615dc7f70e2 100644
--- a/gnot/dat.h
+++ b/gnot/dat.h
@@ -88,7 +88,8 @@ struct Alarm
 #define	CHEXCL	0x20000000L
 struct Chan
 {
-	QLock;				/* general access */
+	QLock	rdl;			/* read access */
+	QLock	wrl;			/* write access */
 	Ref;
 	union{
 		Chan	*next;		/* allocation */
@@ -171,8 +172,8 @@ struct Dev
 	Chan	*(*open)(Chan*, int);
 	void	 (*create)(Chan*, char*, int, ulong);
 	void	 (*close)(Chan*);
-	long	 (*read)(Chan*, void*, long);
-	long	 (*write)(Chan*, void*, long);
+	long	 (*read)(Chan*, void*, long, ulong);
+	long	 (*write)(Chan*, void*, long, ulong);
 	void	 (*remove)(Chan*);
 	void	 (*wstat)(Chan*, char*);
 };
@@ -473,6 +474,7 @@ struct Stream {
 	QLock	rdlock;		/* read lock */
 	Queue	*procq;		/* write queue at process end */
 	Queue	*devq;		/* read queue at device end */
+	Block	*err;		/* error message from down stream */
 };
 #define	RD(q)		((q)->other < (q) ? (q->other) : q)
 #define	WR(q)		((q)->other > (q) ? (q->other) : q)
diff --git a/gnot/devcons.c b/gnot/devcons.c
index b8dcfdceb6e42c7ce300a20b26406958ecbd3517..77852fc6058a1a2c1b4f38e77365f0e4970ba415 100644
--- a/gnot/devcons.c
+++ b/gnot/devcons.c
@@ -269,14 +269,14 @@ pprint(char *fmt, ...)
 		return 0;
 	n = sprint(buf, "%s %d: ", u->p->text, u->p->pid);
 	n = doprint(buf+n, buf+sizeof(buf), fmt, (&fmt+1)) - buf;
-	qlock(c);
+	qlock(&c->wrl);
 	if(waserror()){
-		qunlock(c);
+		qunlock(&c->wrl);
 		return 0;
 	}
-	(*devtab[c->type].write)(c, buf, n);
+	(*devtab[c->type].write)(c, buf, n, c->offset);
 	c->offset += n;
-	qunlock(c);
+	qunlock(&c->wrl);
 	poperror();
 	return n;
 }
@@ -554,7 +554,7 @@ consclose(Chan *c)
 }
 
 long
-consread(Chan *c, void *buf, long n)
+consread(Chan *c, void *buf, long n, ulong offset)
 {
 	int ch, i, j, k;
 	ulong l;
@@ -622,13 +622,13 @@ consread(Chan *c, void *buf, long n)
 		return streamread(c, buf, n);
 
 	case Qrs232ctl:
-		if(c->offset)
+		if(offset)
 			return 0;
 		*(char *)buf = duartinputport();
 		return 1;
 
 	case Qcputime:
-		k = c->offset;
+		k = offset;
 		if(k >= sizeof tmp)
 			return 0;
 		if(k+n > sizeof tmp)
@@ -645,21 +645,21 @@ consread(Chan *c, void *buf, long n)
 		return n;
 
 	case Qpgrpid:
-		return readnum(c->offset, buf, n, u->p->pgrp->pgrpid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->pgrp->pgrpid, NUMSIZE);
 
 	case Qpid:
-		return readnum(c->offset, buf, n, u->p->pid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->pid, NUMSIZE);
 
 	case Qppid:
-		return readnum(c->offset, buf, n, u->p->parentpid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->parentpid, NUMSIZE);
 
 	case Qtime:
-		return readnum(c->offset, buf, n, boottime+TK2SEC(MACHP(0)->ticks), NUMSIZE);
+		return readnum(offset, buf, n, boottime+TK2SEC(MACHP(0)->ticks), NUMSIZE);
 
 	case Qmsec:
-		return readnum(c->offset, buf, n, TK2MS(MACHP(0)->ticks), NUMSIZE);
+		return readnum(offset, buf, n, TK2MS(MACHP(0)->ticks), NUMSIZE);
 	case Qclock:
-		k = c->offset;
+		k = offset;
 		if(k >= 2*NUMSIZE)
 			return 0;
 		if(k+n > 2*NUMSIZE)
@@ -670,7 +670,7 @@ consread(Chan *c, void *buf, long n)
 		return n;
 
 	case Quser:
-		return readstr(c->offset, buf, n, u->p->pgrp->user);
+		return readstr(offset, buf, n, u->p->pgrp->user);
 
 	case Qnull:
 		return 0;
@@ -699,7 +699,7 @@ consread(Chan *c, void *buf, long n)
 }
 
 long
-conswrite(Chan *c, void *va, long n)
+conswrite(Chan *c, void *va, long n, ulong offset)
 {
 	char cbuf[64];
 	char buf[256];
@@ -742,12 +742,12 @@ conswrite(Chan *c, void *va, long n)
 	case Quser:
 		if(u->p->pgrp->user[0])		/* trying to overwrite /dev/user */
 			error(Eperm);
-		if(c->offset >= NAMELEN-1)
+		if(offset >= NAMELEN-1)
 			return 0;
-		if(c->offset+n >= NAMELEN-1)
-			n = NAMELEN-1 - c->offset;
-		memmove(u->p->pgrp->user+c->offset, a, n);
-		u->p->pgrp->user[c->offset+n] = 0;
+		if(offset+n >= NAMELEN-1)
+			n = NAMELEN-1 - offset;
+		memmove(u->p->pgrp->user+offset, a, n);
+		u->p->pgrp->user[offset+n] = 0;
 		break;
 
 	case Qcputime:
diff --git a/gnot/devincon.c b/gnot/devincon.c
index e490d28d11fc44364e5ab143f81c44a78d38c529..f8db939f60f098fdbf0c14d27ad11fc9aed293c2 100644
--- a/gnot/devincon.c
+++ b/gnot/devincon.c
@@ -393,13 +393,13 @@ inconclose(Chan *c)
 }
 
 long	 
-inconread(Chan *c, void *buf, long n)
+inconread(Chan *c, void *buf, long n, ulong offset)
 {
 	return streamread(c, buf, n);
 }
 
 long	 
-inconwrite(Chan *c, void *buf, long n)
+inconwrite(Chan *c, void *buf, long n, ulong offset)
 {
 	return streamwrite(c, buf, n, 0);
 }
diff --git a/gnot/devport.c b/gnot/devport.c
index 5c6dfb031488158176305d88d5c53124e9c4d013..2b1d16be59e9d00eb83cb9cdf07775b409f37754 100644
--- a/gnot/devport.c
+++ b/gnot/devport.c
@@ -106,7 +106,7 @@ portclose(Chan *c)
 {}
 
 long
-portread(Chan *c, char *a, long n)
+portread(Chan *c, char *a, long n, ulong offset)
 {
 	long s, k;
 	if (n == 0)
@@ -115,9 +115,9 @@ portread(Chan *c, char *a, long n)
 	case Qdir:
 		return devdirread(c, a, n, portdir, NPORT, devgen);
 	case Qdata:
-		if (!conf.portispaged || (s = c->offset >> PORTSHIFT) > 0xff)
+		if (!conf.portispaged || (s = offset >> PORTSHIFT) > 0xff)
 			s = -1;
-		k = c->offset % PORTSIZE;
+		k = offset % PORTSIZE;
 		P_qlock(s);
 		switch ((int)n) {
 		case 1:
@@ -139,16 +139,16 @@ portread(Chan *c, char *a, long n)
 }
 
 long
-portwrite(Chan *c, char *a, long n)
+portwrite(Chan *c, char *a, long n, ulong offset)
 {
 	long s, k;
 	if (n == 0)
 		return 0;
 	switch ((int)c->qid.path) {
 	case Qdata:
-		if (!conf.portispaged || (s = c->offset >> PORTSHIFT) > 0xff)
+		if (!conf.portispaged || (s = offset >> PORTSHIFT) > 0xff)
 			s = -1;
-		k = c->offset % PORTSIZE;
+		k = offset % PORTSIZE;
 		P_qlock(s);
 		switch ((int)n) {
 		case 1:
diff --git a/gnot/fns.h b/gnot/fns.h
index f603df37f7defb1f94101ffc6058655a9675a6eb..78e5a1999741368465d5d906d40c097954260ca1 100644
--- a/gnot/fns.h
+++ b/gnot/fns.h
@@ -197,7 +197,7 @@ Stream	*streamnew(ushort, ushort, ushort, Qinfo*, int);
 void	streamopen(Chan*, Qinfo*);
 int	streamparse(char*, Block*);
 void	streamstat(Chan*, char*, char*);
-long	stringread(Chan*, void*, long, char*);
+long	stringread(Chan*, void*, long, char*, ulong);
 long	syscall(Ureg*);
 int	tas(char*);
 void	touser(void);
diff --git a/gnot/main.c b/gnot/main.c
index d864b0efa7ab4f0b6db8af49e2721f55ff979921..e306ca856a6818eb9711d8480485adc7f3299cbb 100644
--- a/gnot/main.c
+++ b/gnot/main.c
@@ -118,13 +118,13 @@ init0(void)
 	u->dot = clone(u->slash, 0);
 	if(!waserror()){
 		c = namec("#e/bootline", Acreate, OWRITE, 0600);
-		(*devtab[c->type].write)(c, bootline, 64);
+		(*devtab[c->type].write)(c, bootline, 64, 0);
 		close(c);
 		c = namec("#e/bootserver", Acreate, OWRITE, 0600);
-		(*devtab[c->type].write)(c, bootserver, 64);
+		(*devtab[c->type].write)(c, bootserver, 64, 0);
 		close(c);
 		c = namec("#e/bootdevice", Acreate, OWRITE, 0600);
-		(*devtab[c->type].write)(c, bootdevice, 2);
+		(*devtab[c->type].write)(c, bootdevice, 2, 0);
 		close(c);
 	}
 	poperror();
diff --git a/gnot/mem.h b/gnot/mem.h
index 31f0783d7089f951d8ca80e099275f58be24c0c6..c3a2873119ebe016d4ad366ae4666d68397de998 100644
--- a/gnot/mem.h
+++ b/gnot/mem.h
@@ -100,3 +100,6 @@
 
 #define	NSEG		5
 #define	MACHSIZE	4096
+
+
+#define isphys(p) ((((ulong)(p))&0xF0000000) == KSEG)
diff --git a/port/dev.c b/port/dev.c
index 84b99bf1336ba0bdc83fd6921e3a8738091db4d9..0d38f024a64e36aa6837e34c487fb98a07e5afce 100644
--- a/port/dev.c
+++ b/port/dev.c
@@ -107,6 +107,12 @@ devwalk(Chan *c, char *name, Dirtab *tab, int ntab, Devgen *gen)
 		}
 }
 
+int devclwalk(Chan *c, Chan *nc, char *name, Dirtab *tab, int ntab, Devgen *gen)
+{
+	c = devclone(c, nc);
+	return devwalk(c, name, tab, ntab, gen);
+}
+
 void
 devstat(Chan *c, char *db, Dirtab *tab, int ntab, Devgen *gen)
 {
diff --git a/port/devbit.c b/port/devbit.c
index e8bbf1db01aefd97cbdd45e753b854bfa3a67b29..edd524745e5d88fc1de2d6f678bc36044b48b323 100644
--- a/port/devbit.c
+++ b/port/devbit.c
@@ -275,7 +275,7 @@ bitclose(Chan *c)
 #define	K2U(x)	(x)
 
 long
-bitread(Chan *c, void *va, long n)
+bitread(Chan *c, void *va, long n, ulong offset)
 {
 	uchar *p, *q;
 	long miny, maxy, t, x, y;
@@ -429,7 +429,7 @@ bitread(Chan *c, void *va, long n)
 		error(Ebadblt);
 
 	case Qscreen:
-		if(c->offset==0){
+		if(offset==0){
 			if(n < 5*12)
 				error(Eio);
 			sprint(va, "%11d %11d %11d %11d %11d ",
@@ -441,7 +441,7 @@ bitread(Chan *c, void *va, long n)
 		}
 		ws = 1<<(3-gscreen.ldepth);	/* pixels per byte */
 		l = (gscreen.r.max.x+ws-1)/ws - gscreen.r.min.x/ws;
-		t = c->offset-5*12;
+		t = offset-5*12;
 		miny = t/l;
 		maxy = (t+n)/l;
 		if(miny >= gscreen.r.max.y)
@@ -467,7 +467,7 @@ bitread(Chan *c, void *va, long n)
 
 
 long
-bitwrite(Chan *c, void *va, long n)
+bitwrite(Chan *c, void *va, long n, ulong offset)
 {
 	uchar *p, *q;
 	long m, v, miny, maxy, minx, maxx, t, x, y, tw, th;
diff --git a/port/devboot.c b/port/devboot.c
index a5880d222b9d84ba6579d1972f53669b7c9e0f16..9e50239f326dafc6e801b1aa4cb45bbf34450109 100644
--- a/port/devboot.c
+++ b/port/devboot.c
@@ -74,7 +74,7 @@ bootclose(Chan *c)
 }
 
 long	 
-bootread(Chan *c, void *buf, long n)
+bootread(Chan *c, void *buf, long n, ulong offset)
 {
 	switch(c->qid.path & ~CHDIR){
 	case Qdir:
@@ -85,21 +85,21 @@ bootread(Chan *c, void *buf, long n)
 }
 
 long	 
-bootwrite(Chan *c, void *buf, long n)
+bootwrite(Chan *c, void *buf, long n, ulong offset)
 {
 	ulong pc;
 
 	switch(c->qid.path & ~CHDIR){
 	case Qmem:
 		/* kernel memory.  BUG: shouldn't be so easygoing. BUG: mem mapping? */
-		if(c->offset>=KZERO && c->offset<KZERO+conf.npage*BY2PG){
+		if(offset>=KZERO && offset<KZERO+conf.npage*BY2PG){
 /*			print("%ux, %d\n", c->offset, n);/**/
-			if(c->offset+n > KZERO+conf.npage*BY2PG)
-				n = KZERO+conf.npage*BY2PG - c->offset;
-			memmove((char*)c->offset, buf, n);
+			if(offset+n > KZERO+conf.npage*BY2PG)
+				n = KZERO+conf.npage*BY2PG - offset;
+			memmove((char*)offset, buf, n);
 			return n;
 		}
-		print("bootwrite: bad addr %lux\n", c->offset);
+		print("bootwrite: bad addr %lux\n", offset);
 		error(Ebadarg);
 
 	case Qboot:
diff --git a/port/devcons.c b/port/devcons.c
index 25e864cdb6826b53843ebfda6961399db40cc6fe..63bc661c716d95663b6561ad240ac56ebd088f1d 100644
--- a/port/devcons.c
+++ b/port/devcons.c
@@ -197,14 +197,14 @@ pprint(char *fmt, ...)
 		return 0;
 	n = sprint(buf, "%s %d: ", u->p->text, u->p->pid);
 	n = doprint(buf+n, buf+sizeof(buf), fmt, (&fmt+1)) - buf;
-	qlock(c);
+	qlock(&c->wrl);
 	if(waserror()){
-		qunlock(c);
+		qunlock(&c->wrl);
 		return 0;
 	}
-	(*devtab[c->type].write)(c, buf, n);
+	(*devtab[c->type].write)(c, buf, n, c->offset);
 	c->offset += n;
-	qunlock(c);
+	qunlock(&c->wrl);
 	poperror();
 	return n;
 }
@@ -435,7 +435,7 @@ consclose(Chan *c)
 }
 
 long
-consread(Chan *c, void *buf, long n)
+consread(Chan *c, void *buf, long n, ulong offset)
 {
 	int ch, i, j, k;
 	ulong l;
@@ -492,7 +492,7 @@ consread(Chan *c, void *buf, long n)
 		return i;
 
 	case Qcputime:
-		k = c->offset;
+		k = offset;
 		if(k >= sizeof tmp)
 			return 0;
 		if(k+n > sizeof tmp)
@@ -509,22 +509,22 @@ consread(Chan *c, void *buf, long n)
 		return n;
 
 	case Qpgrpid:
-		return readnum(c->offset, buf, n, u->p->pgrp->pgrpid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->pgrp->pgrpid, NUMSIZE);
 
 	case Qpid:
-		return readnum(c->offset, buf, n, u->p->pid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->pid, NUMSIZE);
 
 	case Qppid:
-		return readnum(c->offset, buf, n, u->p->parentpid, NUMSIZE);
+		return readnum(offset, buf, n, u->p->parentpid, NUMSIZE);
 
 	case Qtime:
-		return readnum(c->offset, buf, n, boottime+TK2SEC(MACHP(0)->ticks), 12);
+		return readnum(offset, buf, n, boottime+TK2SEC(MACHP(0)->ticks), 12);
 
 	case Quser:
-		return readstr(c->offset, buf, n, u->p->pgrp->user);
+		return readstr(offset, buf, n, u->p->pgrp->user);
 
 	case Qlog:
-		return readlog(c->offset, buf, n);
+		return readlog(offset, buf, n);
 
 	case Qnull:
 		return 0;
@@ -536,7 +536,7 @@ consread(Chan *c, void *buf, long n)
 }
 
 long
-conswrite(Chan *c, void *va, long n)
+conswrite(Chan *c, void *va, long n, ulong offset)
 {
 	char cbuf[64];
 	char buf[256];
@@ -573,12 +573,12 @@ conswrite(Chan *c, void *va, long n)
 	case Quser:
 		if(u->p->pgrp->user[0])		/* trying to overwrite /dev/user */
 			error(Eperm);
-		if(c->offset >= NAMELEN-1)
+		if(offset >= NAMELEN-1)
 			return 0;
-		if(c->offset+n >= NAMELEN-1)
-			n = NAMELEN-1 - c->offset;
-		memmove(u->p->pgrp->user+c->offset, a, n);
-		u->p->pgrp->user[c->offset+n] = 0;
+		if(offset+n >= NAMELEN-1)
+			n = NAMELEN-1 - offset;
+		memmove(u->p->pgrp->user+offset, a, n);
+		u->p->pgrp->user[offset+n] = 0;
 		break;
 
 	case Qcputime:
diff --git a/port/devdk.c b/port/devdk.c
index 32eb3c3f145eea63f441c54e1a40e48f34bc55f6..b21c1ca4588256688d1d19d2a8de693d34f573e2 100644
--- a/port/devdk.c
+++ b/port/devdk.c
@@ -863,7 +863,7 @@ dkclose(Chan *c)
 }
 
 long	 
-dkread(Chan *c, void *a, long n)
+dkread(Chan *c, void *a, long n, ulong offset)
 {
 	Line *lp;
 
@@ -880,17 +880,17 @@ dkread(Chan *c, void *a, long n)
 	lp = &dk[c->dev].line[STREAMID(c->qid.path)];
 	switch(STREAMTYPE(c->qid.path)){
 	case Daddrqid:
-		return stringread(c, a, n, lp->addr);
+		return stringread(c, a, n, lp->addr, offset);
 	case Draddrqid:
-		return stringread(c, a, n, lp->raddr);
+		return stringread(c, a, n, lp->raddr, offset);
 	case Duserqid:
-		return stringread(c, a, n, lp->ruser);
+		return stringread(c, a, n, lp->ruser, offset);
 	}
 	error(Eperm);
 }
 
 long	 
-dkwrite(Chan *c, void *a, long n)
+dkwrite(Chan *c, void *a, long n, ulong offset)
 {
 	int t;
 	char buf[256];
diff --git a/port/devdup.c b/port/devdup.c
index e819bf879284f0e2034d16f085a6835c9a1403e3..4a0ca33f741112bd88a56e38657070233d8deab0 100644
--- a/port/devdup.c
+++ b/port/devdup.c
@@ -104,7 +104,7 @@ dupclose(Chan *c)
 }
 
 long
-dupread(Chan *c, void *va, long n)
+dupread(Chan *c, void *va, long n, ulong offset)
 {
 	char *a = va;
 
@@ -114,7 +114,7 @@ dupread(Chan *c, void *va, long n)
 }
 
 long
-dupwrite(Chan *c, void *va, long n)
+dupwrite(Chan *c, void *va, long n, ulong offset)
 {
 	panic("dupwrite");
 }
diff --git a/port/devenv.c b/port/devenv.c
index b5920d5e552ee5b79f574e71b4a63c1478641109..e450c0ba785c7127997f036d4f0ed1079572b7d5 100644
--- a/port/devenv.c
+++ b/port/devenv.c
@@ -435,7 +435,7 @@ envpgclose(Env *e)
 }
 
 long
-envread(Chan *c, void *va, long n)
+envread(Chan *c, void *va, long n, ulong offset)
 {
 	Env *e;
 	Envval *ev;
@@ -456,19 +456,19 @@ envread(Chan *c, void *va, long n)
 	lock(e);
 	ev = e->val;
 	vn = ev? e->val->len : 0;
-	if(c->offset+n > vn)
-		n = vn - c->offset;
+	if(offset+n > vn)
+		n = vn - offset;
 	if(n <= 0)
 		n = 0;
 	else
-		memmove(a, ev->dat+c->offset, n);
+		memmove(a, ev->dat+offset, n);
 	unlock(e);
 	unlock(pg);
 	return n;
 }
 
 long
-envwrite(Chan *c, void *va, long n)
+envwrite(Chan *c, void *va, long n, ulong offset)
 {
 	Env *e;
 	char *p;
@@ -496,13 +496,13 @@ envwrite(Chan *c, void *va, long n)
 	}
 	if(e->pgref>1)
 		panic("envwrite to non-duped env");
-	growenval(e, c->offset+n);
+	growenval(e, offset+n);
 	ev = e->val;
 	vn = ev? ev->len : 0;
-	if(c->offset > vn)
+	if(offset > vn)
 		error(Egreg); /* perhaps should zero fill */
-	memmove(ev->dat+c->offset, a, n);
-	e->val->len = c->offset+n;
+	memmove(ev->dat+offset, a, n);
+	e->val->len = offset+n;
 	poperror();
 	unlock(e);
 	unlock(&envalloc);
diff --git a/port/deviproute.c b/port/deviproute.c
index bb9c7f2dad1c28e427903a18a7eac3a968e791ea..1c6c2988c54940288205fa3d290088fb751ce717 100644
--- a/port/deviproute.c
+++ b/port/deviproute.c
@@ -268,7 +268,7 @@ iprouteclose(Chan *c)
 #define PAD "                                                                  "
 
 long
-iprouteread(Chan *c, void *a, long n)
+iprouteread(Chan *c, void *a, long n, ulong offset)
 {
 	char	buf[IPR_ENTRYLEN*3];
 	Iproute	*r;
@@ -280,10 +280,10 @@ iprouteread(Chan *c, void *a, long n)
 		return devdirread(c, a, n, iproutetab, Niproutetab, devgen);
 	case Qdata:
 		lock(&iprtab);
-		part = c->offset/IPR_ENTRYLEN;
+		part = offset/IPR_ENTRYLEN;
 		for(r = iprtab.first; part && r; r = r->next)
 			part--;
-		bytes = c->offset;
+		bytes = offset;
 		while(r && bytes < iprtab.n*IPR_ENTRYLEN && n){
 			part = bytes%IPR_ENTRYLEN;
 
@@ -309,7 +309,7 @@ iprouteread(Chan *c, void *a, long n)
 			r = r->next;
 		}
 		unlock(&iprtab);
-		return bytes - c->offset;
+		return bytes - offset;
 		break;
 	default:
 		n=0;
@@ -319,7 +319,7 @@ iprouteread(Chan *c, void *a, long n)
 }
 
 long
-iproutewrite(Chan *c, char *a, long n)
+iproutewrite(Chan *c, char *a, long n, ulong offset)
 {
 	char buf[IPR_ENTRYLEN];
 	char *field[4];
diff --git a/port/devkprof.c b/port/devkprof.c
index a893a0af375995e181b87d4322fb894ef811eecf..09cb6ee78d1c0accc7ea93f1647ed8e17ca0a8ad 100644
--- a/port/devkprof.c
+++ b/port/devkprof.c
@@ -118,19 +118,19 @@ kproferrstr(Error *e, char *buf)
 }
 
 long
-kprofread(Chan *c, void *a, long n)
+kprofread(Chan *c, void *a, long n, ulong offset)
 {
 	switch((int)(c->qid&~CHDIR)){
 	case Kprofdirqid:
 		return devdirread(c, a, n, kproftab, Nkproftab, devgen);
 	case Kprofdataqid:
-		if(c->offset >= NBUF*sizeof timerbuf[0]){
+		if(offset >= NBUF*sizeof timerbuf[0]){
 			n = 0;
 			break;
 		}
-		if(c->offset+n > NBUF*sizeof timerbuf[0])
-			n = NBUF*sizeof timerbuf[0]-c->offset;
-		memmove(a, ((char *)timerbuf)+c->offset, n);
+		if(offset+n > NBUF*sizeof timerbuf[0])
+			n = NBUF*sizeof timerbuf[0]-offset;
+		memmove(a, ((char *)timerbuf)+offset, n);
 		break;
 	default:
 		n=0;
@@ -140,7 +140,7 @@ kprofread(Chan *c, void *a, long n)
 }
 
 long
-kprofwrite(Chan *c, char *a, long n)
+kprofwrite(Chan *c, char *a, long n, ulong offset)
 {
 	switch((int)(c->qid&~CHDIR)){
 	case Kprofstartclrqid:
diff --git a/port/devlance.c b/port/devlance.c
index 705fb7ea26f5a0f2f2c39d00b99efea057e03111..a8011550b0dd3357d27cd670fb34e70c5033ed7c 100644
--- a/port/devlance.c
+++ b/port/devlance.c
@@ -623,40 +623,40 @@ lanceclose(Chan *c)
 }
 
 static long
-lancetraceread(Chan *c, void *a, long n)
+lancetraceread(Chan *c, void *a, long n, ulong offset)
 {
 	char buf[1024];
 	long rv;
 	int i;
 	char *ca = a;
-	int offset;
+	int off;
 	Trace *t;
 	int plen;
 
 	rv = 0;
 	sprintpacket(buf, l.dq.t);
 	plen = strlen(buf);
-	offset = c->offset % plen;
-	for(t = &l.dq.t[c->offset/plen]; n && t < &l.dq.t[Ndpkt]; t++){
+	off = offset % plen;
+	for(t = &l.dq.t[offset/plen]; n && t < &l.dq.t[Ndpkt]; t++){
 		if(t->tag == 0)
 			break;
 		lock(&l.dq);
 		sprintpacket(buf, t);
 		unlock(&l.dq);
-		i = plen - offset;
+		i = plen - off;
 		if(i > n)
 			i = n;
-		memmove(ca, buf + offset, i);
+		memmove(ca, buf + off, i);
 		n -= i;
 		ca += i;
 		rv += i;
-		offset = 0;
+		off = 0;
 	}
 	return rv;
 }
 
 long	 
-lanceread(Chan *c, void *a, long n)
+lanceread(Chan *c, void *a, long n, ulong offset)
 {
 	char buf[256];
 
@@ -668,16 +668,16 @@ lanceread(Chan *c, void *a, long n)
 		l.inpackets, l.outpackets, l.crcs,
 		l.overflows, l.frames, l.buffs, l.oerrs,
 		l.ea[0], l.ea[1], l.ea[2], l.ea[3], l.ea[4], l.ea[5]);
-		return stringread(c, a, n, buf);
+		return stringread(c, a, n, buf, offset);
 	case Ltraceqid:
-		return lancetraceread(c, a, n);
+		return lancetraceread(c, a, n, offset);
 	default:
 		return streamread(c, a, n);
 	}
 }
 
 long	 
-lancewrite(Chan *c, void *a, long n)
+lancewrite(Chan *c, void *a, long n, ulong offset)
 {
 	return streamwrite(c, a, n, 0);
 }
diff --git a/port/devmnt.c b/port/devmnt.c
index 92ab8413c875ea272af20998e7534c0bdd5b6bc8..4de1ed4011cd34711e02e25dd62d9fb1941ef1ff 100644
--- a/port/devmnt.c
+++ b/port/devmnt.c
@@ -504,16 +504,15 @@ mntclose(Chan *c)
 }
 
 long
-mntreadwrite(Chan *c, void *vbuf, long n, int type)
+mntreadwrite(Chan *c, void *vbuf, long n, int type, ulong offset)
 {
 	Mnt *m;
 	Mnthdr *mh;
-	long nt, nr, count, offset;
+	long nt, nr, count;
 	char *buf;
 
 	buf = vbuf;
 	count = 0;
-	offset = c->offset;
 	m = mntdev(c->dev, 0);
 	mh = mhalloc();
 	if(waserror()){
@@ -543,12 +542,12 @@ mntreadwrite(Chan *c, void *vbuf, long n, int type)
 }
 
 long	 
-mntread(Chan *c, void *buf, long n)
+mntread(Chan *c, void *buf, long n, ulong offset)
 {
 	long i;
 	uchar *b;
 
-	n = mntreadwrite(c, buf, n, Tread);
+	n = mntreadwrite(c, buf, n, Tread, offset);
 	if(c->qid.path & CHDIR){
 		b = (uchar*)buf;
 		for(i=n-DIRLEN; i>=0; i-=DIRLEN){
@@ -563,9 +562,9 @@ mntread(Chan *c, void *buf, long n)
 }
 
 long	 
-mntwrite(Chan *c, void *buf, long n)
+mntwrite(Chan *c, void *buf, long n, ulong offset)
 {
-	return mntreadwrite(c, buf, n, Twrite);
+	return mntreadwrite(c, buf, n, Twrite, offset);
 }
 
 void	 
@@ -700,7 +699,7 @@ mntxmit(Mnt *m, Mnthdr *mh)
 		mqfree(q);
 		nexterror();
 	}
-	if((*devtab[q->msg->type].write)(q->msg, mbw->buf, n) != n){
+	if((*devtab[q->msg->type].write)(q->msg, mbw->buf, n, 0) != n){
 		print("short write in mntxmit\n");
 		error(Eshortmsg);
 	}
@@ -713,7 +712,7 @@ mntxmit(Mnt *m, Mnthdr *mh)
 		nexterror();
 	}
 	mh->mbr = mballoc();
-	n = (*devtab[q->msg->type].read)(q->msg, mh->mbr->buf, BUFSIZE);
+	n = (*devtab[q->msg->type].read)(q->msg, mh->mbr->buf, BUFSIZE, 0);
 	poperror();		/* 3 */
 	mqfree(q);
 	poperror();		/* 2 */
@@ -767,7 +766,7 @@ mntxmit(Mnt *m, Mnthdr *mh)
 	}
 	mh->readreply = 0;
 	mh->active = 1;
-	if((*devtab[q->msg->type].write)(q->msg, mbw->buf, n) != n){
+	if((*devtab[q->msg->type].write)(q->msg, mbw->buf, n, 0) != n){
 		print("short write in mntxmit\n");
 		error(Eshortmsg);
 	}
@@ -782,7 +781,7 @@ mntxmit(Mnt *m, Mnthdr *mh)
 			nexterror();
 		}
 		mh->mbr = mballoc();
-		n = (*devtab[q->msg->type].read)(q->msg, mh->mbr->buf, BUFSIZE);
+		n = (*devtab[q->msg->type].read)(q->msg, mh->mbr->buf, BUFSIZE, 0);
 		poperror();		/* 3 */
 		if(convM2S(mh->mbr->buf, &mh->rhdr, n) == 0){
 			mnterrdequeue(m, mh);
diff --git a/port/devnonet.c b/port/devnonet.c
index 4675c9fa10895fde653b2909826152023304edc0..6007b0dd1cf79ea4f7580692ff31d1da4b0e2637 100644
--- a/port/devnonet.c
+++ b/port/devnonet.c
@@ -325,7 +325,7 @@ nonetclose(Chan *c)
 }
 
 long	 
-nonetread(Chan *c, void *a, long n)
+nonetread(Chan *c, void *a, long n, ulong offset)
 {
 	int t;
 	Noconv *cp;
@@ -346,21 +346,21 @@ nonetread(Chan *c, void *a, long n)
 	cp = &noifc[c->dev].conv[STREAMID(c->qid.path)];
 	switch(t){
 	case Nraddrqid:
-		return stringread(c, a, n, cp->raddr);
+		return stringread(c, a, n, cp->raddr, offset);
 	case Naddrqid:
-		return stringread(c, a, n, cp->addr);
+		return stringread(c, a, n, cp->addr, offset);
 	case Nruserqid:
-		return stringread(c, a, n, cp->ruser);
+		return stringread(c, a, n, cp->ruser, offset);
 	case Nstatsqid:
 		sprint(stats, "sent: %d\nrcved: %d\nrexmit: %d\nbad: %d\n",
 			cp->sent, cp->rcvd, cp->rexmit, cp->bad);
-		return stringread(c, a, n, stats);
+		return stringread(c, a, n, stats, offset);
 	}
 	error(Eperm);
 }
 
 long	 
-nonetwrite(Chan *c, void *a, long n)
+nonetwrite(Chan *c, void *a, long n, ulong offset)
 {
 	int t;
 	int m;
diff --git a/port/devpipe.c b/port/devpipe.c
index 2bb0d21f70a81b3b6e75d09f81c1c86c35eeb855..e41a1b8f87c437005af0b3a4af1ee940a9afbdda 100644
--- a/port/devpipe.c
+++ b/port/devpipe.c
@@ -241,7 +241,7 @@ pipeclose(Chan *c)
 }
 
 long
-piperead(Chan *c, void *va, long n)
+piperead(Chan *c, void *va, long n, ulong offset)
 {
 	if(c->qid.path & CHDIR)
 		return devdirread(c, va, n, pipedir, NPIPEDIR, pipegen);
@@ -254,7 +254,7 @@ piperead(Chan *c, void *va, long n)
  *  the process.
  */
 long
-pipewrite(Chan *c, void *va, long n)
+pipewrite(Chan *c, void *va, long n, ulong offset)
 {
 	if(waserror()){
 		postnote(u->p, 1, "sys: write on closed pipe", NExit);
diff --git a/port/devproc.c b/port/devproc.c
index ee38027aa463b1dbd7645885d884e086466519e7..6ee99317128caa505c9bdb5967cda42b615ee6d4 100644
--- a/port/devproc.c
+++ b/port/devproc.c
@@ -144,9 +144,9 @@ procopen(Chan *c, int omode)
 			goto Close;
 		if(p->pid != PID(c->qid))
 			goto Close;
-		qlock(tc);
+		qlock(&tc->rdl);
 		tc->offset = 0;
-		qunlock(tc);
+		qunlock(&tc->rdl);
 		return tc;
 	case Qctl:
 	case Qnote:
@@ -206,7 +206,7 @@ procclose(Chan * c)
 }
 
 long
-procread(Chan *c, void *va, long n)
+procread(Chan *c, void *va, long n, ulong offset)
 {
 	char *a = va, *b;
 	char statbuf[2*NAMELEN+12+6*12];
@@ -236,9 +236,9 @@ procread(Chan *c, void *va, long n)
 		/*
 		 * One page at a time
 		 */
-		if(((c->offset+n)&~(BY2PG-1)) != (c->offset&~(BY2PG-1)))
-			n = BY2PG - (c->offset&(BY2PG-1));
-		s = seg(p, c->offset);
+		if(((offset+n)&~(BY2PG-1)) != (offset&~(BY2PG-1)))
+			n = BY2PG - (offset&(BY2PG-1));
+		s = seg(p, offset);
 		if(s){
 			o = s->o;
 			if(o == 0)
@@ -248,11 +248,11 @@ procread(Chan *c, void *va, long n)
 				unlock(o);
 				error(Eprocdied);
 			}
-			if(seg(p, c->offset) != s){
+			if(seg(p, offset) != s){
 				unlock(o);
 				error(Egreg);
 			}
-			pte = &o->pte[(c->offset-o->va)>>PGSHIFT];
+			pte = &o->pte[(offset-o->va)>>PGSHIFT];
 			if(s->mod){
 				opte = pte;
 				while(pte = pte->nextmod)	/* assign = */
@@ -264,35 +264,35 @@ procread(Chan *c, void *va, long n)
 			pg = pte->page;
 			unlock(o);
 			if(pg == 0){
-				pprint("nonresident page addr %lux (complain to rob)\n", c->offset);
+				pprint("nonresident page addr %lux (complain to rob)\n", offset);
 				memset(a, 0, n);
 			}else{
 				k = kmap(pg);
 				b = (char*)VA(k);
-				memmove(a, b+(c->offset&(BY2PG-1)), n);
+				memmove(a, b+(offset&(BY2PG-1)), n);
 				kunmap(k);
 			}
 			return n;
 		}
 		/* u area */
-		if(c->offset>=USERADDR && c->offset<USERADDR+BY2PG){
-			if(c->offset+n > USERADDR+BY2PG)
-				n = USERADDR+BY2PG - c->offset;
+		if(offset>=USERADDR && offset<USERADDR+BY2PG){
+			if(offset+n > USERADDR+BY2PG)
+				n = USERADDR+BY2PG - offset;
 			pg = p->upage;
 			if(pg==0 || p->pid!=PID(c->qid))
 				error(Eprocdied);
 			k = kmap(pg);
 			b = (char*)VA(k);
-			memmove(a, b+(c->offset-USERADDR), n);
+			memmove(a, b+(offset-USERADDR), n);
 			kunmap(k);
 			return n;
 		}
 
 		/* kernel memory.  BUG: shouldn't be so easygoing. BUG: mem mapping? */
-		if(c->offset>=KZERO && c->offset<KZERO+conf.npage0*BY2PG){
-			if(c->offset+n > KZERO+conf.npage0*BY2PG)
-				n = KZERO+conf.npage0*BY2PG - c->offset;
-			memmove(a, (char*)c->offset, n);
+		if(offset>=KZERO && offset<KZERO+conf.npage0*BY2PG){
+			if(offset+n > KZERO+conf.npage0*BY2PG)
+				n = KZERO+conf.npage0*BY2PG - offset;
+			memmove(a, (char*)offset, n);
 			return n;
 		}
 		return 0;
@@ -328,18 +328,18 @@ procread(Chan *c, void *va, long n)
 		return n;
 
 	case Qproc:
-		if(c->offset >= sizeof(Proc))
+		if(offset >= sizeof(Proc))
 			return 0;
-		if(c->offset+n > sizeof(Proc))
-			n = sizeof(Proc) - c->offset;
-		memmove(a, ((char*)p)+c->offset, n);
+		if(offset+n > sizeof(Proc))
+			n = sizeof(Proc) - offset;
+		memmove(a, ((char*)p)+offset, n);
 		return n;
 
 	case Qstatus:
-		if(c->offset >= sizeof statbuf)
+		if(offset >= sizeof statbuf)
 			return 0;
-		if(c->offset+n > sizeof statbuf)
-			n = sizeof statbuf - c->offset;
+		if(offset+n > sizeof statbuf)
+			n = sizeof statbuf - offset;
 		sprint(statbuf, "%-27s %-27s %-11s ", p->text, p->pgrp->user, statename[p->state]);
 		for(i=0; i<6; i++){
 			l = p->time[i];
@@ -348,7 +348,7 @@ procread(Chan *c, void *va, long n)
 			l = TK2MS(l);
 			readnum(0, statbuf+2*NAMELEN+12+NUMSIZE*i, NUMSIZE, l, NUMSIZE);
 		}
-		memmove(a, statbuf+c->offset, n);
+		memmove(a, statbuf+offset, n);
 		return n;
 	}
 	error(Egreg);
@@ -356,7 +356,7 @@ procread(Chan *c, void *va, long n)
 
 
 long
-procwrite(Chan *c, void *va, long n)
+procwrite(Chan *c, void *va, long n, ulong offset)
 {
 	Proc *p;
 	Pgrp *pg;
diff --git a/port/devroot.c b/port/devroot.c
index 1e03267debdf268b180b44792c50a106ee04f784..2394b9f97ba5f6e3bc1d82a1b83f46d6418c0888 100644
--- a/port/devroot.c
+++ b/port/devroot.c
@@ -90,7 +90,7 @@ rootclose(Chan *c)
 #include	"boot.h"
 
 long	 
-rootread(Chan *c, void *buf, long n)
+rootread(Chan *c, void *buf, long n, ulong offset)
 {
 
 	switch(c->qid.path & ~CHDIR){
@@ -98,19 +98,19 @@ rootread(Chan *c, void *buf, long n)
 		return devdirread(c, buf, n, rootdir, nroot, devgen);
 
 	case Qboot:		/* boot */
-		if(c->offset >= sizeof bootcode)
+		if(offset >= sizeof bootcode)
 			return 0;
-		if(c->offset+n > sizeof bootcode)
-			n = sizeof bootcode - c->offset;
-		memmove(buf, ((char*)bootcode)+c->offset, n);
+		if(offset+n > sizeof bootcode)
+			n = sizeof bootcode - offset;
+		memmove(buf, ((char*)bootcode)+offset, n);
 		return n;
 
 	case Qcfs:		/* cfs */
-		if(c->offset >= cfslen)
+		if(offset >= cfslen)
 			return 0;
-		if(c->offset+n > cfslen)
-			n = cfslen - c->offset;
-		memmove(buf, ((char*)cfscode)+c->offset, n);
+		if(offset+n > cfslen)
+			n = cfslen - offset;
+		memmove(buf, ((char*)cfscode)+offset, n);
 		return n;
 
 	case Qdev:
@@ -121,7 +121,7 @@ rootread(Chan *c, void *buf, long n)
 }
 
 long	 
-rootwrite(Chan *c, void *buf, long n)
+rootwrite(Chan *c, void *buf, long n, ulong offset)
 {
 	error(Egreg);
 }
diff --git a/port/devscsi.c b/port/devscsi.c
index 4393ca5d25bcc61b67c319c875f2725cc398e8de..770062251c80b5990d950e8774066fbd5931102d 100644
--- a/port/devscsi.c
+++ b/port/devscsi.c
@@ -117,7 +117,7 @@ scsiclose(Chan *c)
 {}
 
 long
-scsiread(Chan *c, char *a, long n)
+scsiread(Chan *c, char *a, long n, ulong offset)
 {
 	Scsi *cmd = &staticcmd;
 	if (n == 0)
@@ -125,7 +125,7 @@ scsiread(Chan *c, char *a, long n)
 	if(c->qid.path & CHDIR)
 		return devdirread(c, a, n, 0, 0, scsigen);
 	if(c->qid.path==1){
-		if(c->offset == 0){
+		if(offset == 0){
 			*a = ownid;
 			n = 1;
 		}else
@@ -155,7 +155,7 @@ scsiread(Chan *c, char *a, long n)
 		memmove(a, cmd->data.base, n);
 		break;
 	case Qdebug:
-		if (c->offset == 0) {
+		if (offset == 0) {
 			n=1;
 			*a="01"[debugs[(c->qid.path>>4)&7]!=0];
 		} else
@@ -168,11 +168,11 @@ scsiread(Chan *c, char *a, long n)
 }
 
 long
-scsiwrite(Chan *c, char *a, long n)
+scsiwrite(Chan *c, char *a, long n, ulong offset)
 {
 	Scsi *cmd = &staticcmd;
 	if(c->qid.path==1 && n>0){
-		if(c->offset == 0){
+		if(offset == 0){
 			n = 1;
 			ownid=*a;
 			scsiinit();
@@ -204,7 +204,7 @@ scsiwrite(Chan *c, char *a, long n)
 		n = cmd->data.ptr - cmd->data.base;
 		break;
 	case Qdebug:
-		if (c->offset == 0) {
+		if (offset == 0) {
 			debugs[(c->qid.path>>4)&7] = (*a=='1');
 			n = 1;
 		} else
diff --git a/port/devsrv.c b/port/devsrv.c
index 6ac0d9c82e257532ed0da692fcdf1f222d248137..21ed942feb748e9a348d84b34b43a9fe90a14e78 100644
--- a/port/devsrv.c
+++ b/port/devsrv.c
@@ -231,13 +231,11 @@ srvdirentry(Entry *e, char *a, long count){
 }
 
 long
-srvread(Chan *c, void *va, long n)
+srvread(Chan *c, void *va, long n, ulong offset)
 {
 	Entry *dir, *e;
-	int offset;
 
 	dir = c->aux;
-	offset = c->offset;
 	isdir(c);
 	if(n <= 0)
 		return 0;
@@ -257,7 +255,7 @@ srvread(Chan *c, void *va, long n)
 }
 
 long
-srvwrite(Chan *c, void *va, long n)
+srvwrite(Chan *c, void *va, long n, ulong offset)
 {
 	Entry *e;
 	int i, fd;
diff --git a/port/devwren.c b/port/devwren.c
index 42cfb827346465f44f0e4f0654f0f9409d09dcee..d60ac4b9330f1e7cc6fb0d7a40a2a03f4c706b47 100644
--- a/port/devwren.c
+++ b/port/devwren.c
@@ -202,7 +202,7 @@ wrenclose(Chan *c)
 #define	PSHORT(p, v)		((p)[0]=(v), (p)[1]=((v)>>8))
 #define	PLONG(p, v)		(PSHORT(p, (v)), PSHORT(p+2, (v)>>16))
 long
-wrenread(Chan *c, char *a, long n)
+wrenread(Chan *c, char *a, long n, ulong offset)
 {
 	Scsi *cmd = &staticcmd;
 	unsigned long lbn;
@@ -219,9 +219,9 @@ wrenread(Chan *c, char *a, long n)
 	p = &(d->p[Mask&c->qid.path]);
 	switch ((int)(c->qid.path & ~Mask)) {
 	case Qdata:
-		if (n % d->blocksize || c->offset % d->blocksize)
+		if (n % d->blocksize || offset % d->blocksize)
 			error(Ebadarg);
-		lbn = (c->offset/d->blocksize) + p->firstblock;
+		lbn = (offset/d->blocksize) + p->firstblock;
 		if (lbn >= p->maxblock)
 			error(Ebadarg);
 		if (n > sizeof datablk)
@@ -252,7 +252,7 @@ wrenread(Chan *c, char *a, long n)
 	case Qstruct:
 		if (n < 8)
 			error(Ebadarg);
-		if (c->offset >= 8)
+		if (offset >= 8)
 			return 0;
 		n = 8;
 		PLONG((uchar *)&a[0], p->maxblock - p->firstblock);
@@ -265,7 +265,7 @@ wrenread(Chan *c, char *a, long n)
 }
 
 long
-wrenwrite(Chan *c, char *a, long n)
+wrenwrite(Chan *c, char *a, long n, ulong offset)
 {
 	Scsi *cmd = &staticcmd;
 	unsigned long lbn;
@@ -279,9 +279,9 @@ wrenwrite(Chan *c, char *a, long n)
 	p = &(d->p[Mask&c->qid.path]);
 	switch ((int)(c->qid.path & ~Mask)) {
 	case Qdata:
-		if (n % d->blocksize || c->offset % d->blocksize)
+		if (n % d->blocksize || offset % d->blocksize)
 			error(Ebadarg);
-		lbn = c->offset/d->blocksize + p->firstblock;
+		lbn = offset/d->blocksize + p->firstblock;
 		if (lbn >= p->maxblock)
 			error(Ebadarg);
 		if (n > sizeof datablk)
diff --git a/port/fault.c b/port/fault.c
index 8d97e775f863fd42f73eeef09ab54f86398cb535..fe479170c16c71feeb90d64dae2f3ea8d1480f7a 100644
--- a/port/fault.c
+++ b/port/fault.c
@@ -79,20 +79,19 @@ fault(ulong addr, int read)
 				n = BY2PG;
 			pg = newpage(1, o, addr);
 			k = kmap(pg);
-			qlock(o->chan);
+			qlock(&o->chan->rdl);
 			if(waserror()){
 				kunmap(k);
-				qunlock(o->chan);
+				qunlock(&o->chan->rdl);
 				pg->o = 0;
 				pg->ref--;
 				pexit("load i/o error", 0);
 			}
-			o->chan->offset = (addr-o->va) + o->minca;
 			l = (char*)VA(k);
-			if((*devtab[o->chan->type].read)(o->chan, l, n) != n)
+			if((*devtab[o->chan->type].read)(o->chan, l, n, (addr-o->va) + o->minca) != n)
 				error(Eioload);
 			flushpage(pg->pa);
-			qunlock(o->chan);
+			qunlock(&o->chan->rdl);
 			if(n<BY2PG)
 				memset(l+n, 0, BY2PG-n);
 			lock(o);
diff --git a/port/stream.c b/port/stream.c
index f8ad0ed0268eee8762ab6254d5ed26f429df4a98..13f8b4686cdfd2a539ab8f42212ed02a39e6907f 100644
--- a/port/stream.c
+++ b/port/stream.c
@@ -790,6 +790,7 @@ streamnew(ushort type, ushort dev, ushort id, Qinfo *qi, int noopen)
 	s->type = type;
 	s->dev = dev;
 	s->id = id;
+	s->err = 0;
 
 	/*
  	 *  hang a device and process q off the stream
@@ -801,6 +802,8 @@ streamnew(ushort type, ushort dev, ushort id, Qinfo *qi, int noopen)
 		s->opens = 1;
 	s->hread = 0;
 	q = allocq(&procinfo);
+	WR(q)->ptr = s;
+	RD(q)->ptr = s;
 	s->procq = WR(q);
 	q = allocq(qi);
 	s->devq = RD(q);
@@ -895,6 +898,8 @@ streamexit(Stream *s, int locked)
 			freeq(q);
 		}
 		s->id = s->dev = s->type = 0;
+		if(s->err)
+			freeb(s->err);
 	}
 	s->inuse--;
 	rv = s->inuse;
@@ -972,9 +977,14 @@ void
 stputq(Queue *q, Block *bp)
 {
 	int delim;
+	Stream *s;
 
 	if(bp->type == M_HANGUP){
-		freeb(bp);
+		s = q->ptr;
+		if(bp->rptr<bp->wptr && s->err==0)
+			s->err = bp;
+		else
+			freeb(bp);
 		q->flag |= QHUNGUP;
 		q->other->flag |= QHUNGUP;
 		wakeup(q->other->rp);
@@ -1009,17 +1019,17 @@ stputq(Queue *q, Block *bp)
  *  read a string.  update the offset accordingly.
  */
 long
-stringread(Chan *c, uchar *buf, long n, char *str)
+stringread(Chan *c, uchar *buf, long n, char *str, ulong offset)
 {
 	long i;
 
 	i = strlen(str);
-	i -= c->offset;
+	i -= offset;
 	if(i<n)
 		n = i;
 	if(n<0)
 		return 0;
-	memmove(buf, str + c->offset, n);
+	memmove(buf, str + offset, n);
 	return n;
 }
 
@@ -1036,7 +1046,7 @@ streamctlread(Chan *c, void *vbuf, long n)
 	s = c->stream;
 	if(STREAMTYPE(c->qid.path) == Sctlqid){
 		sprint(num, "%d", s->id);
-		return stringread(c, buf, n, num);
+		return stringread(c, buf, n, num, c->offset);
 	} else {
 		if(CHDIR & c->qid.path)
 			return devdirread(c, vbuf, n, 0, 0, streamgen);
@@ -1091,7 +1101,9 @@ streamread(Chan *c, void *vbuf, long n)
 		bp = getq(q);
 		if(bp == 0){
 			if(q->flag & QHUNGUP){
-				if(s->hread++ < 3)
+				if(s->err)
+					errors((char*)s->err->rptr);
+				else if(s->hread++<3)
 					break;
 				else
 					error(Ehungup);
@@ -1246,8 +1258,12 @@ streamwrite(Chan *c, void *a, long n, int docopy)
 	 *  No writes allowed on hungup channels
 	 */
 	q = s->procq;
-	if(q->other->flag & QHUNGUP)
-		error(Ehungup);
+	if(q->other->flag & QHUNGUP){
+		if(s->err)
+			errors((char*)(s->err->rptr));
+		else
+			error(Ehungup);
+	}
 
 	if(!docopy && isphys(a)){
 		/*
diff --git a/port/sysfile.c b/port/sysfile.c
index 2f7e60e65827bd95f78b2abeaf35e2493a6ca210..bd4f3d15c93a5900c29c79705d1ddff09ba8dcac 100644
--- a/port/sysfile.c
+++ b/port/sysfile.c
@@ -191,7 +191,7 @@ unionread(Chan *c, void *va, long n)
 	}
 	nc = (*devtab[nc->type].open)(nc, OREAD);
 	nc->offset = c->offset;
-	nr = (*devtab[nc->type].read)(nc, va, n);
+	nr = (*devtab[nc->type].read)(nc, va, n, nc->offset);
 	c->offset = nc->offset;		/* devdirread e.g. changes it */
 	close(nc);
 	poperror();
@@ -226,9 +226,9 @@ sysread(ulong *arg)
 
 	c = fdtochan(arg[0], OREAD);
 	validaddr(arg[1], arg[2], 1);
-	qlock(c);
+	qlock(&c->rdl);
 	if(waserror()){
-		qunlock(c);
+		qunlock(&c->rdl);
 		nexterror();
 	}
 	n = arg[2];
@@ -240,9 +240,9 @@ sysread(ulong *arg)
 	if((c->qid.path&CHDIR) && (c->flag&CMOUNT))
 		n = unionread(c, (void*)arg[1], n);
 	else
-		n = (*devtab[c->type].read)(c, (void*)arg[1], n);
+		n = (*devtab[c->type].read)(c, (void*)arg[1], n, c->offset);
 	c->offset += n;
-	qunlock(c);
+	qunlock(&c->rdl);
 	return n;
 }
 
@@ -254,16 +254,16 @@ syswrite(ulong *arg)
 
 	c = fdtochan(arg[0], OWRITE);
 	validaddr(arg[1], arg[2], 0);
-	qlock(c);
+	qlock(&c->wrl);
 	if(waserror()){
-		qunlock(c);
+		qunlock(&c->wrl);
 		nexterror();
 	}
 	if(c->qid.path & CHDIR)
 		error(Eisdir);
-	n = (*devtab[c->type].write)(c, (void*)arg[1], arg[2]);
+	n = (*devtab[c->type].write)(c, (void*)arg[1], arg[2], c->offset);
 	c->offset += n;
-	qunlock(c);
+	qunlock(&c->wrl);
 	return n;
 }
 
@@ -280,9 +280,11 @@ sysseek(ulong *arg)
 		error(Eisdir);
 	if(devchar[c->type] == '|')
 		error(Eisstream);
-	qlock(c);
+	qlock(&c->rdl);
+	qlock(&c->wrl);
 	if(waserror()){
-		qunlock(c);
+		qunlock(&c->rdl);
+		qunlock(&c->wrl);
 		nexterror();
 	}
 	switch(arg[2]){
@@ -301,7 +303,8 @@ sysseek(ulong *arg)
 		break;
 	}
 	off = c->offset;
-	qunlock(c);
+	qunlock(&c->rdl);
+	qunlock(&c->wrl);
 	poperror();
 	return off;
 }
diff --git a/port/sysproc.c b/port/sysproc.c
index c18a7ffb433953d6944baad89a2ce455217307e6..efe8c10418818be2cf8aebf023e47d3cd20ae555 100644
--- a/port/sysproc.c
+++ b/port/sysproc.c
@@ -170,7 +170,7 @@ sysexec(ulong *arg)
 	}
 	if(!indir)
 		strcpy(elem, u->elem);
-	n = (*devtab[tc->type].read)(tc, &exec, sizeof(Exec));
+	n = (*devtab[tc->type].read)(tc, &exec, sizeof(Exec), 0);
 	if(n < 2)
     Err:
 		error(Ebadexec);
diff --git a/power/dat.h b/power/dat.h
index 6fe5ae70f1c91675a89bad55b1ce2946b99157b0..78760657ffcb14128e2e64023ab2b231b91fcbf6 100644
--- a/power/dat.h
+++ b/power/dat.h
@@ -106,7 +106,8 @@ struct Hotmsg
 #define	CHDIR	0x80000000L
 struct Chan
 {
-	QLock;				/* general access */
+	QLock	rdl;			/* read access */
+	QLock	wrl;			/* write access */
 	Ref;
 	union{
 		Chan	*next;		/* allocation */
@@ -181,8 +182,8 @@ struct Dev
 	Chan	*(*open)(Chan*, int);
 	void	 (*create)(Chan*, char*, int, ulong);
 	void	 (*close)(Chan*);
-	long	 (*read)(Chan*, void*, long);
-	long	 (*write)(Chan*, void*, long);
+	long	 (*read)(Chan*, void*, long, ulong);
+	long	 (*write)(Chan*, void*, long, ulong);
 	void	 (*remove)(Chan*);
 	void	 (*wstat)(Chan*, char*);
 };
@@ -481,6 +482,7 @@ struct Stream {
 	QLock	rdlock;		/* read lock */
 	Queue	*procq;		/* write queue at process end */
 	Queue	*devq;		/* read queue at device end */
+	Block	*err;		/* error message from down stream */
 };
 #define	RD(q)		((q)->other < (q) ? (q->other) : q)
 #define	WR(q)		((q)->other > (q) ? (q->other) : q)
diff --git a/power/devbit3.c b/power/devbit3.c
index 1411db4748b26ee5a05dfb96c1a0848c6cd87b6b..b17cf5112ed1b830b2b3a6d980859e662251118f 100644
--- a/power/devbit3.c
+++ b/power/devbit3.c
@@ -130,7 +130,7 @@ bit3close(Chan *c)
  */
 
 long	 
-bit3read(Chan *c, void *buf, long n)
+bit3read(Chan *c, void *buf, long n, ulong offset)
 {
 	Bit3msg *bp;
 	int docpy;
@@ -174,7 +174,7 @@ bit3read(Chan *c, void *buf, long n)
 }
 
 long	 
-bit3write(Chan *c, void *buf, long n)
+bit3write(Chan *c, void *buf, long n, ulong offset)
 {
 	Bit3msg *bp;
 
diff --git a/power/devhotrod.c b/power/devhotrod.c
index 2148283edda007d295ab999f5b99822a8a7af4bd..51af70930fcfb4c5f6fc355fa7b8a2a742889df9 100644
--- a/power/devhotrod.c
+++ b/power/devhotrod.c
@@ -272,7 +272,7 @@ hotmsgintr(Hotmsg *hm)
  */
 
 long	 
-hotrodread(Chan *c, void *buf, long n)
+hotrodread(Chan *c, void *buf, long n, ulong offset)
 {
 	Hotrod *hp;
 	Hotmsg *mp, **hmp;
@@ -389,7 +389,7 @@ hotrodread(Chan *c, void *buf, long n)
 }
 
 long	 
-hotrodwrite(Chan *c, void *buf, long n)
+hotrodwrite(Chan *c, void *buf, long n, ulong offset)
 {
 	Hotrod *hp;
 	Hotmsg *mp, **hmp;
diff --git a/power/devhs.c b/power/devhs.c
index a10da8b439aa53bccf8d76b87ec34ba42f738b09..0e890244385962e04bf33e09a3d7c0a564f7d8bb 100644
--- a/power/devhs.c
+++ b/power/devhs.c
@@ -218,13 +218,13 @@ hsvmeclose(Chan *c)
 }
 
 long	 
-hsvmeread(Chan *c, void *buf, long n)
+hsvmeread(Chan *c, void *buf, long n, ulong offset)
 {
 	return streamread(c, buf, n);
 }
 
 long	 
-hsvmewrite(Chan *c, void *buf, long n)
+hsvmewrite(Chan *c, void *buf, long n, ulong offset)
 {
 	return streamwrite(c, buf, n, 0);
 }
diff --git a/power/devrtc.c b/power/devrtc.c
index dde09fb9777f9245d726c8fafdd5880cbc84a91d..c1709ed6279a78da7dfcf6f68316bd173cf751ab 100644
--- a/power/devrtc.c
+++ b/power/devrtc.c
@@ -137,7 +137,7 @@ rtcclose(Chan *c)
 #define GETBCD(o) ((bcdclock[o]&0xf) + 10*(bcdclock[o]>>4))
 
 long	 
-rtcread(Chan *c, void *buf, long n)
+rtcread(Chan *c, void *buf, long n, ulong offset)
 {
 	int i,j;
 	uchar ch;
@@ -192,13 +192,13 @@ rtcread(Chan *c, void *buf, long n)
 	else
 		rtc.year += 1900;
 
-	return readnum(c->offset, buf, n, rtc2sec(&rtc), 12);
+	return readnum(offset, buf, n, rtc2sec(&rtc), 12);
 }
 
 #define PUTBCD(n,o) bcdclock[o] = (n % 10) | (((n / 10) % 10)<<4)
 
 long	 
-rtcwrite(Chan *c, void *buf, long n)
+rtcwrite(Chan *c, void *buf, long n, ulong offset)
 {
 	Rtc rtc;
 	ulong secs;
@@ -208,7 +208,7 @@ rtcwrite(Chan *c, void *buf, long n)
 	uchar *nv;
 	char *cp, *ep;
 
-	if(c->offset!=0)
+	if(offset!=0)
 		error(Ebadarg);
 
 	/*
diff --git a/power/fns.h b/power/fns.h
index ea727ebb9c7ab21f48aaebd5f611aa6215274996..b6d453cc7fe581d77733139c5bc9c38ba962cda2 100644
--- a/power/fns.h
+++ b/power/fns.h
@@ -186,7 +186,7 @@ Stream	*streamnew(ushort, ushort, ushort, Qinfo*, int);
 void	streamopen(Chan*, Qinfo*);
 int	streamparse(char*, Block*);
 void	streamstat(Chan*, char*, char*);
-long	stringread(Chan*, void*, long, char*);
+long	stringread(Chan*, void*, long, char*, ulong);
 long	syscall(Ureg*);
 void	sysloginit(void);
 void	syslog(char*, int);
diff --git a/ss/dat.h b/ss/dat.h
index 309aca30fc54d0be7cb6edc6a4b10fa4a2f45646..ac8b2c16bffa753a8646e07348ae7ec298ee8c92 100644
--- a/ss/dat.h
+++ b/ss/dat.h
@@ -173,8 +173,8 @@ struct Dev
 	Chan	*(*open)(Chan*, int);
 	void	 (*create)(Chan*, char*, int, ulong);
 	void	 (*close)(Chan*);
-	long	 (*read)(Chan*, void*, long);
-	long	 (*write)(Chan*, void*, long);
+	long	 (*read)(Chan*, void*, long, ulong);
+	long	 (*write)(Chan*, void*, long, ulong );
 	void	 (*remove)(Chan*);
 	void	 (*wstat)(Chan*, char*);
 };
@@ -478,6 +478,7 @@ struct Stream {
 	QLock	rdlock;		/* read lock */
 	Queue	*procq;		/* write queue at process end */
 	Queue	*devq;		/* read queue at device end */
+	Block	*err;		/* error message from down stream */
 };
 #define	RD(q)		((q)->other < (q) ? (q->other) : q)
 #define	WR(q)		((q)->other > (q) ? (q->other) : q)
diff --git a/ss/mem.h b/ss/mem.h
index b2abcdf1cbc0cf333fbe690a137099f6ad82d0fd..9506c291ed9b595a65b93d4382d4f1cb497660a7 100644
--- a/ss/mem.h
+++ b/ss/mem.h
@@ -132,4 +132,4 @@
 #define	NSEG		5
 #define	MACHSIZE	4096
 
-#define isphys(x) ((((ulong)(x)&0xF0000000) == KZERO)
+#define isphys(x) (((ulong)(x)&0xF0000000) == KZERO)