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kernel: make pio() interruptable, avoid copy when doing single-page I/O

When we get interrupted during I/O, make pio()/fixfault()
return with -1 into fault(). Then fault() checks up->procctl
and handles if we got killed.

Also, handle a I/O with size <= BY2PG using Dev.read instead
of Dev.pread. This can avoid extra copy (for example in
the case when devdrawp is on a disk).

--- a/sys/src/9/port/fault.c

+++ b/sys/src/9/port/fault.c

@@ -17,6 +17,7 @@

 	if(up->nerrlab) {

 		if(up->kp == 0)

 			postnote(up, 1, buf, NDebug);

+		up->psstate = nil;

 		error(s);

 	}

 	pprint("suicide: %s\n", buf);

@@ -33,16 +34,15 @@

 	postnote(up, 1, buf, NDebug);

 }

-static void

+static int

 pio(Segment *s, uintptr addr, uintptr soff, Page **p)

 {

 	KMap *k;

 	Chan *c;

 	int n, ask;

-	uintptr o, daddr, paddr;

+	uintptr daddr, vaddr;

 	Page *loadrec, *new;

 	Image *image;

-	Block *b;

 retry:

 	loadrec = *p;

@@ -53,7 +53,7 @@

 		if(new != nil) {

 			*p = new;

 			s->used++;

-			return;

+			return 0;

 		}

 		ask = image->c->iounit;

@@ -64,10 +64,9 @@

 		daddr = soff & -ask;

 		if(daddr+ask > s->flen)

 			ask = s->flen-daddr;

-		paddr = s->base + daddr;

+		vaddr = s->base + daddr;

 		daddr += s->fstart;

-	}

-	else {			/* from a swap image */

+	} else {		/* from a swap image */

 		daddr = swapaddr(loadrec);

 		image = swapimage;

 		new = lookpage(image, daddr);

@@ -75,51 +74,75 @@

 			*p = new;

 			s->swapped--;

 			putswap(loadrec);

-			return;

+			return 0;

 		}

-		paddr = addr;

+		vaddr = addr;

 		ask = BY2PG;

 	}

 	qunlock(s);

 	c = image->c;

-	while(waserror()) {

+	if(waserror()) {

 		if(strcmp(up->errstr, Eintr) == 0)

-			continue;

+			return -1;

 		faulterror(Eioload, c);

 	}

-	b = devtab[c->type]->bread(c, ask, daddr);

-	if(waserror()){

-		freeblist(b);

-		nexterror();

-	}

-	for(o = 0; o < ask; o += BY2PG){

-		new = lookpage(image, daddr + o);

-		if(new != nil){

-			putpage(new);

-			continue;

-		}

-		new = newpage(paddr + o, nil);

-		new->daddr = daddr + o;

+	if(ask <= BY2PG) {

+		new = newpage(vaddr, nil);

+		new->daddr = daddr;

 		k = kmap(new);

-		n = ask - o;

-		if(n > BY2PG)

-			n = BY2PG;

-		else if(n < BY2PG)

-			memset((uchar*)VA(k)+n, 0, BY2PG-n);

-		if(readblist(b, (uchar*)VA(k), n, o) != n){

+		if(waserror()){

 			kunmap(k);

 			putpage(new);

-			error(Eshort);

+			nexterror();

 		}

+		n = devtab[c->type]->read(c, (uchar*)VA(k), ask, daddr);

+		if(n != ask)

+			error(Eshort);

+		if(n < BY2PG)

+			memset((uchar*)VA(k)+n, 0, BY2PG-n);

 		kunmap(k);

 		settxtflush(new, s->flushme);

 		cachepage(new, image);

 		putpage(new);

+		poperror();

+	} else {

+		uintptr o;

+		Block *b;

+

+		b = devtab[c->type]->bread(c, ask, daddr);

+		if(waserror()){

+			freeblist(b);

+			nexterror();

+		}

+		for(o = 0; o < ask; o += BY2PG){

+			new = lookpage(image, daddr + o);

+			if(new != nil){

+				putpage(new);

+				continue;

+			}

+			new = newpage(vaddr + o, nil);

+			new->daddr = daddr + o;

+			k = kmap(new);

+			n = ask - o;

+			if(n > BY2PG)

+				n = BY2PG;

+			else if(n < BY2PG)

+				memset((uchar*)VA(k)+n, 0, BY2PG-n);

+			if(readblist(b, (uchar*)VA(k), n, o) != n){

+				kunmap(k);

+				putpage(new);

+				error(Eshort);

+			}

+			kunmap(k);

+			settxtflush(new, s->flushme);

+			cachepage(new, image);

+			putpage(new);

+		}

+		freeblist(b);

+		poperror();

 	}

-	freeblist(b);

 	poperror();

-	poperror();

 	qlock(s);

 	/*

@@ -128,7 +151,7 @@

 	 *  s was unlocked

 	 */

 	if(*p != loadrec && !pagedout(*p))

-		return;

+		return 0;

 	goto retry;

 }

@@ -166,9 +189,10 @@

 		panic("fault");

 	case SG_TEXT: 			/* Demand load */

-		if(pagedout(*pg))

-			pio(s, addr, soff, pg);

-

+		if(pagedout(*pg)){

+			if(pio(s, addr, soff, pg) < 0)

+				return -1;

+		}

 		mmuphys = PPN((*pg)->pa) | PTERONLY | PTECACHED | PTEVALID;

 		(*pg)->modref = PG_REF;

 		break;

@@ -185,9 +209,10 @@

 		}

 		/* wet floor */

 	case SG_DATA:			/* Demand load/pagein/copy on write */

-		if(pagedout(*pg))

-			pio(s, addr, soff, pg);

-

+		if(pagedout(*pg)){

+			if(pio(s, addr, soff, pg) < 0)

+				return -1;

+		}

 		/*

 		 *  It's only possible to copy on write if

 		 *  we're the only user of the segment.

-- 

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