[PATCH] uml: Fix handling of failed execs of helpers

There were some bugs in handling failures to exec helper programs.  errno was
passed back from the child with the wrong sign.  It was also ignored.  In the
case where it mattered, the errno from the (successful) read in the parent was
used instead.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/os-Linux/helper.c

@@ -42,7 +42,7 @@ static int helper_child(void *arg)
 	if(data->pre_exec != NULL)
 		(*data->pre_exec)(data->pre_data);
 	execvp(argv[0], argv);
-	errval = errno;
+	errval = -errno;
 	printk("helper_child - execve of '%s' failed - errno = %d\n", argv[0], errno);
 	os_write_file(data->fd, &errval, sizeof(errval));
 	kill(os_getpid(), SIGKILL);
@@ -62,7 +62,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
 		stack = *stack_out;
 	else stack = alloc_stack(0, __cant_sleep());
 	if(stack == 0)
-		return(-ENOMEM);
+		return -ENOMEM;
 
 	ret = os_pipe(fds, 1, 0);
 	if(ret < 0){
@@ -95,16 +95,16 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
 	/* Read the errno value from the child, if the exec failed, or get 0 if
 	 * the exec succeeded because the pipe fd was set as close-on-exec. */
 	n = os_read_file(fds[0], &ret, sizeof(ret));
-	if (n < 0) {
-		printk("run_helper : read on pipe failed, ret = %d\n", -n);
-		ret = n;
-		kill(pid, SIGKILL);
-		CATCH_EINTR(waitpid(pid, NULL, 0));
-	} else if(n != 0){
-		CATCH_EINTR(n = waitpid(pid, NULL, 0));
-		ret = -errno;
-	} else {
+	if(n == 0)
 		ret = pid;
+	else {
+		if(n < 0){
+			printk("run_helper : read on pipe failed, ret = %d\n",
+			       -n);
+			ret = n;
+			kill(pid, SIGKILL);
+		}
+		CATCH_EINTR(waitpid(pid, NULL, 0));
 	}
 
 out_close: