Linux Virtualization - Sep 2018 - [RFC] UAPI: Check headers by compiling all together as C++

Here's a set of patches that inserts a step into the build process to make
sure that the UAPI headers can all be built together with C++ (if the
compiler being used supports C++).

Note that it's based on a commit from the sound tree to fix usage of u32
and co..

Most of the patches perform fixups, including:

 (1) Fix member names that conflict with C++ reserved words by providing
     alternates that can be used anywhere.  An anonymous union is used so
     that that the conflicting name is still available outside of C++.

 (2) Fix the use of flexible arrays in structs that get embedded (which is
     illegal in C++).

 (3) Remove the use of internal kernel structs in UAPI structures.

 (4) Fix symbol collisions.

 (5) Fix use of sparsely initialised arrays (which g++ doesn't implement).

 (6) Remove some use of PAGE_SIZE since this isn't valid outside of the
     kernel.

There's also:

 (7) Move the coda_psdev.h header file to fs/coda/.

And lastly:

 (8) Compile all of the UAPI headers (with a few exceptions) together as
     C++ to catch new errors occurring as part of the regular build
     process.

Changes for v2:

 - Merge commit from sound tree to fix u32 usage issues
 - Use a switch to fix sparse array initialisation
 - Simplify nilfs2 by performing bitwise ops in LE space not CPU space
 - Handle conflicting fix to use of 'private' in keyctl.h
 - Move kernel internal coda bits to coda internal headers
 - Move coda_psdev.h header to fs/coda/.

The patches can also be found here:

	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=uapi-check

Thanks,
David
---
David Howells (11):
      UAPI: drm: Fix use of C++ keywords as structural members
      UAPI: keys: Fix use of C++ keywords as structural members
      UAPI: virtio_net: Fix use of C++ keywords as structural members
      UAPI: bcache: Fix use of embedded flexible array
      UAPI: coda: Move kernel internals out of public view
      coda: Move internal defs out of include/linux/
      UAPI: netfilter: Fix symbol collision issues
      UAPI: nilfs2: Fix use of undefined byteswapping functions
      UAPI: ndctl: Fix g++-unsupported initialisation in headers
      UAPI: ndctl: Remove use of PAGE_SIZE
      UAPI: Check headers build for C++


 Makefile                                          |    1 
 fs/coda/cache.c                                   |    2 
 fs/coda/cnode.c                                   |    2 
 fs/coda/coda_linux.c                              |    2 
 fs/coda/coda_psdev.h                              |   88 +++++++++++++++
 fs/coda/dir.c                                     |    2 
 fs/coda/file.c                                    |    3 -
 fs/coda/inode.c                                   |    2 
 fs/coda/pioctl.c                                  |    3 -
 fs/coda/psdev.c                                   |    3 -
 fs/coda/symlink.c                                 |    3 -
 fs/coda/upcall.c                                  |    2 
 include/linux/coda_psdev.h                        |   72 ------------
 include/linux/ndctl.h                             |   22 ++++
 include/uapi/drm/i810_drm.h                       |    7 +
 include/uapi/drm/msm_drm.h                        |    7 +
 include/uapi/linux/bcache.h                       |    2 
 include/uapi/linux/coda_psdev.h                   |   18 ---
 include/uapi/linux/keyctl.h                       |    7 +
 include/uapi/linux/ndctl.h                        |   52 ++++-----
 include/uapi/linux/netfilter/nfnetlink_cthelper.h |    2 
 include/uapi/linux/netfilter_ipv4/ipt_ECN.h       |    9 --
 include/uapi/linux/nilfs2_ondisk.h                |   28 ++---
 include/uapi/linux/virtio_net.h                   |    7 +
 scripts/headers-c++.sh                            |  124 +++++++++++++++++++++
 25 files changed, 304 insertions(+), 166 deletions(-)
 create mode 100644 fs/coda/coda_psdev.h
 delete mode 100644 include/linux/coda_psdev.h
 create mode 100644 include/linux/ndctl.h
 create mode 100755 scripts/headers-c++.sh

The virtio_net_ctrl_hdr struct uses a C++ keyword as structural members.  Fix
this by inserting an anonymous union that provides an alternative name and
then hide the reserved name in C++.

Signed-off-by: David Howells <dhowells at redhat.com>
cc: "Michael S. Tsirkin" <mst at redhat.com>
cc: Jason Wang <jasowang at redhat.com>
cc: virtualization at lists.linux-foundation.org
---

 include/uapi/linux/virtio_net.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index a3715a3224c1..967142bc0e05 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -150,7 +150,12 @@ struct virtio_net_hdr_mrg_rxbuf {
  * command goes in between.
  */
 struct virtio_net_ctrl_hdr {
-	__u8 class;
+	union {
+#ifndef __cplusplus
+		__u8 class;
+#endif
+		__u8 _class;
+	};
 	__u8 cmd;
 } __attribute__((packed));

On Thu, Sep 06, 2018 at 10:18:42AM +0100, David Howells
wrote:
> The virtio_net_ctrl_hdr struct uses a C++ keyword as structural members. 
Fix
> this by inserting an anonymous union that provides an alternative name and
> then hide the reserved name in C++.
> 
> Signed-off-by: David Howells <dhowells at redhat.com>
> cc: "Michael S. Tsirkin" <mst at redhat.com>
> cc: Jason Wang <jasowang at redhat.com>
> cc: virtualization at lists.linux-foundation.org
> ---
> 
>  include/uapi/linux/virtio_net.h |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> index a3715a3224c1..967142bc0e05 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -150,7 +150,12 @@ struct virtio_net_hdr_mrg_rxbuf {
>   * command goes in between.
>   */
>  struct virtio_net_ctrl_hdr {
> -	__u8 class;
> +	union {
> +#ifndef __cplusplus
> +		__u8 class;
> +#endif
> +		__u8 _class;
> +	};
>  	__u8 cmd;
>  } __attribute__((packed));
>  
So if we are going to do this, I think I'd prefer something like:

struct virtio_net_ctrl_hdr_v2 {
	__u8 cmd_class;
  	__u8 cmd;
};

And then hide the whole old structure. This also gets rid of the packed
keyword which we don't really need here.

Only issue is virtio_net_ctrl_hdr_v2 is ugly. But oh well.

And then rework at least QEMU to use the v2 of the header.

Quite a bit of churn, so I don't think it makes sense to apply just this
one in isolation - only if rest of the changes go in.


-- 
MST