[PATCH] uml: preserve errno in error paths

The poster child for this patch is the third tuntap_user hunk.  When an ioctl
fails, it properly closes the opened file descriptor and returns.  However,
the close resets errno to 0, and the 'return errno' that follows returns 0
rather than the value that ioctl set.  This caused the caller to believe that
the device open succeeded and had opened file descriptor 0, which caused no
end of interesting behavior.

The rest of this patch is a pass through the UML sources looking for places
where errno could be reset before being passed back out.  A common culprit is
printk, which could call write, being called before errno is returned.

In some cases, where the code ends up being much smaller, I just deleted the
printk.

There was another case where a caller of run_helper looked at errno after a
failure, rather than the return value of run_helper, which was the errno value
that it wanted.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 4b83c6c..4ba9b17 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -75,7 +75,7 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
 	struct msghdr msg;
 	struct cmsghdr *cmsg;
 	struct iovec iov;
-	int pid, n;
+	int pid, n, err;
 
 	sprintf(version_buf, "%d", UML_NET_VERSION);
 
@@ -105,9 +105,10 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
 	n = recvmsg(me, &msg, 0);
 	*used_out = n;
 	if(n < 0){
+		err = -errno;
 		printk("tuntap_open_tramp : recvmsg failed - errno = %d\n", 
 		       errno);
-		return(-errno);
+		return err;
 	}
 	CATCH_EINTR(waitpid(pid, NULL, 0));
 
@@ -147,9 +148,10 @@ static int tuntap_open(void *data)
 		ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
 		strlcpy(ifr.ifr_name, pri->dev_name, sizeof(ifr.ifr_name));
 		if(ioctl(pri->fd, TUNSETIFF, (void *) &ifr) < 0){
+			err = -errno;
 			printk("TUNSETIFF failed, errno = %d\n", errno);
 			os_close_file(pri->fd);
-			return(-errno);
+			return err;
 		}
 	}
 	else {