[RFC] UAPI: Check headers by compiling all together as C++

[RFC] UAPI: Check headers by compiling all together as C++

[David Howells]

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++).  All but the final patch 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) Replace usage of u32 and co. with __u32 and co.

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

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

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.

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: Don't use internal kernel structs in UAPI
      UAPI: netfilter: Fix symbol collision issues
      UAPI: nilfs2: Fix use of undefined byteswapping functions
      UAPI: sound: Fix use of u32 and co. in UAPI headers
      UAPI: ndctl: Fix g++-unsupported initialisation in headers
      UAPI: ndctl: Remove use of PAGE_SIZE
      UAPI: Check headers build for C++


 Makefile                                          |    1 
 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                   |    4 +
 include/uapi/linux/keyctl.h                       |    7 +
 include/uapi/linux/ndctl.h                        |   20 ++-
 include/uapi/linux/netfilter/nfnetlink_cthelper.h |    2 
 include/uapi/linux/netfilter_ipv4/ipt_ECN.h       |    9 --
 include/uapi/linux/nilfs2_ondisk.h                |   21 ++--
 include/uapi/linux/virtio_net.h                   |    7 +
 include/uapi/sound/skl-tplg-interface.h           |  106 +++++++++---------
 scripts/headers-c++.sh                            |  124 +++++++++++++++++++++
 14 files changed, 255 insertions(+), 84 deletions(-)
 create mode 100644 include/linux/ndctl.h
 create mode 100755 scripts/headers-c++.sh

[PATCH 07/11] UAPI: nilfs2: Fix use of undefined byteswapping functions

[David Howells]

nilfs2 exports a load of inline functions to userspace that call kernel
byteswapping functions that don't exist in UAPI.  Fix this by making it
#include asm/byteorder.h and use the functions declared there.

A better way is probably to remove these inline functions from the nilfs2
header since they are technically broken.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
cc: linux-nilfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
---

 include/uapi/linux/nilfs2_ondisk.h |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/nilfs2_ondisk.h b/include/uapi/linux/nilfs2_ondisk.h
index a7e66ab11d1d..d3bd2fe08791 100644
--- a/include/uapi/linux/nilfs2_ondisk.h
+++ b/include/uapi/linux/nilfs2_ondisk.h
@@ -29,6 +29,7 @@
 
 #include <linux/types.h>
 #include <linux/magic.h>
+#include <asm/byteorder.h>
 
 
 #define NILFS_INODE_BMAP_SIZE	7
@@ -533,19 +534,19 @@ enum {
 static inline void							\
 nilfs_checkpoint_set_##name(struct nilfs_checkpoint *cp)		\
 {									\
-	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) |		\
+	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) |	\
 				   (1UL << NILFS_CHECKPOINT_##flag));	\
 }									\
 static inline void							\
 nilfs_checkpoint_clear_##name(struct nilfs_checkpoint *cp)		\
 {									\
-	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) &		\
+	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) &	\
 				   ~(1UL << NILFS_CHECKPOINT_##flag));	\
 }									\
 static inline int							\
 nilfs_checkpoint_##name(const struct nilfs_checkpoint *cp)		\
 {									\
-	return !!(le32_to_cpu(cp->cp_flags) &				\
+	return !!(__le32_to_cpu(cp->cp_flags) &				\
 		  (1UL << NILFS_CHECKPOINT_##flag));			\
 }
 
@@ -595,20 +596,20 @@ enum {
 static inline void							\
 nilfs_segment_usage_set_##name(struct nilfs_segment_usage *su)		\
 {									\
-	su->su_flags = cpu_to_le32(le32_to_cpu(su->su_flags) |		\
+	su->su_flags = __cpu_to_le32(__le32_to_cpu(su->su_flags) |	\
 				   (1UL << NILFS_SEGMENT_USAGE_##flag));\
 }									\
 static inline void							\
 nilfs_segment_usage_clear_##name(struct nilfs_segment_usage *su)	\
 {									\
 	su->su_flags =							\
-		cpu_to_le32(le32_to_cpu(su->su_flags) &			\
+		__cpu_to_le32(__le32_to_cpu(su->su_flags) &		\
 			    ~(1UL << NILFS_SEGMENT_USAGE_##flag));      \
 }									\
 static inline int							\
 nilfs_segment_usage_##name(const struct nilfs_segment_usage *su)	\
 {									\
-	return !!(le32_to_cpu(su->su_flags) &				\
+	return !!(__le32_to_cpu(su->su_flags) &				\
 		  (1UL << NILFS_SEGMENT_USAGE_##flag));			\
 }
 
@@ -619,15 +620,15 @@ NILFS_SEGMENT_USAGE_FNS(ERROR, error)
 static inline void
 nilfs_segment_usage_set_clean(struct nilfs_segment_usage *su)
 {
-	su->su_lastmod = cpu_to_le64(0);
-	su->su_nblocks = cpu_to_le32(0);
-	su->su_flags = cpu_to_le32(0);
+	su->su_lastmod = __cpu_to_le64(0);
+	su->su_nblocks = __cpu_to_le32(0);
+	su->su_flags = __cpu_to_le32(0);
 }
 
 static inline int
 nilfs_segment_usage_clean(const struct nilfs_segment_usage *su)
 {
-	return !le32_to_cpu(su->su_flags);
+	return !__le32_to_cpu(su->su_flags);
 }
 
 /**

Re: [RFC] UAPI: Check headers by compiling all together as C++

[Greg KH]

On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> 
> 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++).  All but the final patch perform fixups,
> including:

Wait, why do we care?  What has recently changed to start to directly
import kernel uapi files into C++ code?

And if userspace wants to do this, can't they do the C namespace trick
themselves when they do the import?  That must be how they are doing it
today, right?

thanks,

greg k-h

Re: [RFC] UAPI: Check headers by compiling all together as C++

[Yann Droneaud]

Hi,

Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > 
> > 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++).  All but the final patch perform fixups,
> > including:
> 
> Wait, why do we care?  What has recently changed to start to directly
> import kernel uapi files into C++ code?
> 
> And if userspace wants to do this, can't they do the C namespace trick
> themselves when they do the import?  That must be how they are doing it
> today, right?
> 

They can't.


Adding extern "C" { } doesn't magically make "class" a non keyword.
Even if it was the case, writing C++ code using whatever->class would
probably broke because class is a keyword in C++.

-- 
Yann Droneaud
OPTEYA


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Re: [RFC] UAPI: Check headers by compiling all together as C++

[Michael S. Tsirkin]

On Wed, Sep 05, 2018 at 07:33:38PM +0200, Yann Droneaud wrote:
> Hi,
> 
> Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> > On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > > 
> > > 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++).  All but the final patch perform fixups,
> > > including:
> > 
> > Wait, why do we care?  What has recently changed to start to directly
> > import kernel uapi files into C++ code?
> > 
> > And if userspace wants to do this, can't they do the C namespace trick
> > themselves when they do the import?  That must be how they are doing it
> > today, right?
> > 
> 
> They can't.
> 
> 
> Adding extern "C" { } doesn't magically make "class" a non keyword.
> Even if it was the case, writing C++ code using whatever->class would
> probably broke because class is a keyword in C++.

I think it's a bug in the language TBH.

> -- 
> Yann Droneaud
> OPTEYA
> 
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Re: [RFC] UAPI: Check headers by compiling all together as C++

[Jan Engelhardt]

On Wednesday 2018-09-05 18:55, Greg KH wrote:

>On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
>> 
>> 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++).  All but the final patch perform fixups,
>> including:
>
>Wait, why do we care?  What has recently changed to start to directly
>import kernel uapi files into C++ code?

With C++11, C++ has become a much nicer language to use (for userspace, anyway).

>And if userspace wants to do this, can't they do the C namespace trick
>themselves when they do the import?

The only trick is to use an extra C source file and extensively wrap things.

Re: [PATCH 07/11] UAPI: nilfs2: Fix use of undefined byteswapping functions

[Al Viro]

On Wed, Sep 05, 2018 at 04:55:23PM +0100, David Howells wrote:
>  nilfs_checkpoint_set_##name(struct nilfs_checkpoint *cp)		\
>  {									\
> -	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) |		\
> +	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) |	\
>  				   (1UL << NILFS_CHECKPOINT_##flag));	\

How about sanitiziung the damn thing to
	cp->cp_flags |= __cpu_to_le32(1UL << NILFS_CHECKPOINT_##flag));

while you are at it?  Or, perhaps, even
#define NILFS2_CP_FLAG(flag) __cpu_to_le32(1UL << NILFS_CHECKPOINT_##flag)

and cp->cp_flags |= NILFS2_CP_FLAG(flag) for this one,

>  }									\
>  static inline void							\
>  nilfs_checkpoint_clear_##name(struct nilfs_checkpoint *cp)		\
>  {									\
> -	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) &		\
> +	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) &	\
>  				   ~(1UL << NILFS_CHECKPOINT_##flag));	\
	cp->cp_flags &= ~NILFS2_CP_FLAG(flag);
here

>  }									\
>  static inline int							\
>  nilfs_checkpoint_##name(const struct nilfs_checkpoint *cp)		\
>  {									\
> -	return !!(le32_to_cpu(cp->cp_flags) &				\
> +	return !!(__le32_to_cpu(cp->cp_flags) &				\
>  		  (1UL << NILFS_CHECKPOINT_##flag));			\

and !!(cp->cp_flags & NILFS2_CP_FLAG(flag)
here?  Or maybe even make the damn thing bool and lose the !! here...

)>  }
>  

and similar for those:

> @@ -595,20 +596,20 @@ enum {
>  static inline void							\
>  nilfs_segment_usage_set_##name(struct nilfs_segment_usage *su)		\
>  {									\
> -	su->su_flags = cpu_to_le32(le32_to_cpu(su->su_flags) |		\
> +	su->su_flags = __cpu_to_le32(__le32_to_cpu(su->su_flags) |	\
>  				   (1UL << NILFS_SEGMENT_USAGE_##flag));\
>  }									\
>  static inline void							\
>  nilfs_segment_usage_clear_##name(struct nilfs_segment_usage *su)	\
>  {									\
>  	su->su_flags =							\
> -		cpu_to_le32(le32_to_cpu(su->su_flags) &			\
> +		__cpu_to_le32(__le32_to_cpu(su->su_flags) &		\
>  			    ~(1UL << NILFS_SEGMENT_USAGE_##flag));      \
>  }									\
>  static inline int							\
>  nilfs_segment_usage_##name(const struct nilfs_segment_usage *su)	\
>  {									\
> -	return !!(le32_to_cpu(su->su_flags) &				\
> +	return !!(__le32_to_cpu(su->su_flags) &				\
>  		  (1UL << NILFS_SEGMENT_USAGE_##flag));			\
>  }



> @@ -619,15 +620,15 @@ NILFS_SEGMENT_USAGE_FNS(ERROR, error)
>  static inline void
>  nilfs_segment_usage_set_clean(struct nilfs_segment_usage *su)
>  {
> -	su->su_lastmod = cpu_to_le64(0);
> -	su->su_nblocks = cpu_to_le32(0);
> -	su->su_flags = cpu_to_le32(0);
> +	su->su_lastmod = __cpu_to_le64(0);
> +	su->su_nblocks = __cpu_to_le32(0);
> +	su->su_flags = __cpu_to_le32(0);
>  }
>  
>  static inline int
>  nilfs_segment_usage_clean(const struct nilfs_segment_usage *su)
>  {
> -	return !le32_to_cpu(su->su_flags);
> +	return !__le32_to_cpu(su->su_flags);

"Check that after byteswap it becomes 0", is it?  How is that different
from return !su->su_flags; ?

Re: [RFC] UAPI: Check headers by compiling all together as C++

[Yann Droneaud]

Le mercredi 05 septembre 2018 à 19:33 +0200, Yann Droneaud a écrit :
> Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> > On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > > 
> > > 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++).  All but the final patch
> > > perform fixups,
> > > including:
> > 
> > Wait, why do we care?  What has recently changed to start to
> > directly
> > import kernel uapi files into C++ code?
> > 
> > And if userspace wants to do this, can't they do the C namespace
> > trick
> > themselves when they do the import?  That must be how they are
> > doing it
> > today, right?
> > 
> 
> They can't.
> 
> 
> Adding extern "C" { } doesn't magically make "class" a non keyword.
> Even if it was the case, writing C++ code using whatever->class would
> probably broke because class is a keyword in C++.
> 

For the record, libX11 has to handle the kink pf issue with C++
keyword:


https://gitlab.freedesktop.org/xorg/lib/libx11/blob/733f64bfeb311c1d040b2f751bfdef9c9d0f89ef/include/X11/Xlib.h#L227

typedef struct {
	XExtData *ext_data;	/* hook for extension to hang data */
	VisualID visualid;	/* visual id of this visual */
#if defined(__cplusplus) || defined(c_plusplus)
	int c_class;		/* C++ class of screen (monochrome, etc.) */
#else
	int class;		/* class of screen (monochrome, etc.) */
#endif
	unsigned long red_mask, green_mask, blue_mask;	/* mask values */
	int bits_per_rgb;	/* log base 2 of distinct color values */
	int map_entries;	/* color map entries */
} Visual;


Regards.

-- 
Yann Droneaud
OPTEYA


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[RFC] UAPI: Check headers by compiling all together as C++

[David Howells]

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

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