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devenv: fix ORCLOSE handling

when opening a /env file ORCLOSE, and the process exits, envgrp() would
return nil can crash in envremove() because procexit will have set up->egrp
to nil before calling closefgrp().

the solution is to capture the environment on open, keeping a reference in
Chan.aux, so it doesnt matter on what process the close happens and a
env chan will always refer to its original environment group.

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

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

@@ -132,8 +132,10 @@

 			runlock(eg);

 	}

 	c->mode = openmode(omode);

-	c->flag |= COPEN;

+	incref(eg);

+	c->aux = eg;

 	c->offset = 0;

+	c->flag |= COPEN;

 	return c;

 }

@@ -181,7 +183,8 @@

 	wunlock(eg);

 	poperror();

-

+	incref(eg);

+	c->aux = eg;

 	c->offset = 0;

 	c->mode = omode;

 	c->flag |= COPEN;

@@ -214,13 +217,19 @@

 static void

 envclose(Chan *c)

 {

-	/*

-	 * cclose can't fail, so errors from remove will be ignored.

-	 * since permissions aren't checked,

-	 * envremove can't not remove it if its there.

-	 */

-	if(c->flag & CRCLOSE)

-		envremove(c);

+	if(c->flag & COPEN){

+		/*

+		 * cclose can't fail, so errors from remove will be ignored.

+		 * since permissions aren't checked,

+		 * envremove can't not remove it if its there.

+		 */

+		if(c->flag & CRCLOSE && !waserror()){

+			envremove(c);

+			poperror();

+		}

+		closeegrp((Egrp*)c->aux);

+		c->aux = nil;

+	}

 }

 static long

@@ -350,7 +359,7 @@

 {

 	Evalue *e, *ee;

-	if(decref(eg) == 0){

+	if(decref(eg) == 0 && eg != &confegrp){

 		e = eg->ent;

 		for(ee = e + eg->nent; e < ee; e++){

 			free(e->name);