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devfs/devsd: fix waserror() and unused variable compiler problem

the compiler optimizes setting unused variables out, which is
problematic if they are used in waserror() handler which the
compiler isnt aware of. rearrange the code to avoid this problem.

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

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

@@ -748,29 +748,33 @@

 	} else

 		mustrd = 1;

-	/* read it */

-	cc = nil;

-	c = nil;

-	if (waserror()){

-		if (cc != nil)

-			cclose(cc);

-		if (c)

-			free(c);

-		if (!mustrd)

+	if(waserror()){

+		if(!mustrd)

 			return;

 		nexterror();

 	}

+

+	/* read it */

 	cc = namec(s, Aopen, OREAD, 0);

+	if(waserror()){

+		cclose(cc);

+		nexterror();

+	}

 	devtab[cc->type]->read(cc, confstr, sizeof confstr, 0);

+	poperror();

 	cclose(cc);

-	cc = nil;

 	/* validate, copy and erase config; mconfig will repopulate confstr */

 	if (strncmp(confstr, cfgstr, sizeof cfgstr - 1) != 0)

 		error("bad #k config, first line must be: 'fsdev:\\n'");

+

+	c = nil;

 	kstrdup(&c, confstr + sizeof cfgstr - 1);

+	if(waserror()){

+		free(c);

+		nexterror();

+	}

 	memset(confstr, 0, sizeof confstr);

-

 	/* process config copy one line at a time */

 	for (p = c; p != nil && *p != '\0'; p = e){

 		e = strchr(p, '\n');

@@ -780,8 +784,10 @@

 			e++;

 		mconfig(p, e - p);

 	}

-	USED(cc);		/* until now, can be used in waserror clause */

 	poperror();

+	free(c);

+

+	poperror();	/* mustrd */

 }

 static int

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

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

@@ -1558,10 +1558,10 @@

 	d = nil;

 	if(waserror()){

-		free(d);

 		qunlock(&unit->ctl);

 		if(sdev != nil)

 			decref(&sdev->r);

+		free(d);

 		nexterror();

 	}

@@ -1600,13 +1600,11 @@

 		error(Eperm);

 	if(d[0].mode != ~0UL)

 		perm->perm = (perm->perm & ~0777) | (d[0].mode & 0777);

-

-	free(d);

-	d = nil; USED(d);

+	poperror();

 	qunlock(&unit->ctl);

 	if(sdev != nil)

 		decref(&sdev->r);

-	poperror();

+	free(d);

 	return n;

 }