Re: [PATCH] VSOCK: fix uapi/linux/vm_sockets.h incomplete types

On Tue, Sep 19, 2017 at 10:38:40AM -0700, David Miller wrote:

From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 18 Sep 2017 16:21:00 +0100

quoted

On Fri, Sep 15, 2017 at 02:14:32PM -0700, David Miller wrote:

quoted

quoted

diff --git a/include/uapi/linux/vm_sockets.h b/include/uapi/linux/vm_sockets.h
index b4ed5d895699..4ae5c625ac56 100644
--- a/include/uapi/linux/vm_sockets.h
+++ b/include/uapi/linux/vm_sockets.h

@@ -18,6 +18,10 @@
 
 #include <linux/socket.h>
 
+#ifndef __KERNEL__
+#include <sys/socket.h> /* struct sockaddr */
+#endif
+

There is no precedence whatsoever to include sys/socket.h in _any_ UAPI
header file provided by the kernel.

<linux/if.h> does it for the same reason:

include/uapi/linux/if.h:#include <sys/socket.h>                 /* for struct sockaddr.         */

You don't need it for struct sockaddr, you need it for sa_family_t,
the comment is very misleading.

Please do as I have instructed and it will fix this problem.

No, you really cannot rely on struct sockaddr from <linux/socket.h> in
uapi headers.  You can check this yourself:

  $ cd /tmp && gcc -o a.o -c /usr/include/linux/vm_sockets.h
  /usr/include/linux/vm_sockets.h:148:32: error: invalid application of ‘sizeof’ to incomplete type ‘struct sockaddr’
  unsigned char svm_zero[sizeof(struct sockaddr) -
                                ^~~~~~

The weird situation is:

1. When compiling the kernel, <linux/socket.h> brings in struct sockaddr
   because the compiler finds include/linux/socket.h first before
   include/uapi/linux/socket.h.

2. When compiling a userspace application, <linux/socket.h> does not
   bring in struct sockaddr because include/uapi/linux/socket.h is
   found.

This is why I added the #include <sys/socket> when !__KERNEL__.  Sorry
that the commit description wasn't clear on this.

Am I misunderstanding something?

Stefan