[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

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[PATCH 09/11] UAPI: ndctl: Fix g++-unsupported initialisation in headers

[David Howells]

The following code in the linux/ndctl header file:

	static inline const char *nvdimm_bus_cmd_name(unsigned cmd)
	{
		static const char * const names[] = {
			[ND_CMD_ARS_CAP] = "ars_cap",
			[ND_CMD_ARS_START] = "ars_start",
			[ND_CMD_ARS_STATUS] = "ars_status",
			[ND_CMD_CLEAR_ERROR] = "clear_error",
			[ND_CMD_CALL] = "cmd_call",
		};

		if (cmd < ARRAY_SIZE(names) && names[cmd])
			return names[cmd];
		return "unknown";
	}

is broken in a number of ways:

 (1) ARRAY_SIZE() is not generally defined.  Fix this by defining a label
     in the enum that indicates the number of commands.

 (2) g++ does not support "non-trivial" array initialisers fully yet.  Fix
     this by defining the missing intermediate values.

 (3) Every file that calls this function will acquire a copy of names[].

The same goes for nvdimm_cmd_name().

A better way would be to remove these functions and their arrays from the
header entirely.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Dan Williams <dan.j.williams@intel.com>
cc: linux-nvdimm@lists.01.org
---

 include/uapi/linux/ndctl.h |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
index 7e27070b9440..9c89159f6a0f 100644
--- a/include/uapi/linux/ndctl.h
+++ b/include/uapi/linux/ndctl.h
@@ -117,6 +117,7 @@ enum {
 	ND_CMD_VENDOR_EFFECT_LOG = 8,
 	ND_CMD_VENDOR = 9,
 	ND_CMD_CALL = 10,
+	nr__ND_CMD = 11
 };
 
 enum {
@@ -128,22 +129,29 @@ enum {
 
 static inline const char *nvdimm_bus_cmd_name(unsigned cmd)
 {
-	static const char * const names[] = {
+	static const char * const names[nr__ND_CMD] = {
+		[0] = NULL,
 		[ND_CMD_ARS_CAP] = "ars_cap",
 		[ND_CMD_ARS_START] = "ars_start",
 		[ND_CMD_ARS_STATUS] = "ars_status",
 		[ND_CMD_CLEAR_ERROR] = "clear_error",
+		[5] = NULL,
+		[6] = NULL,
+		[7] = NULL,
+		[8] = NULL,
+		[9] = NULL,
 		[ND_CMD_CALL] = "cmd_call",
 	};
 
-	if (cmd < ARRAY_SIZE(names) && names[cmd])
+	if (cmd < nr__ND_CMD && names[cmd])
 		return names[cmd];
 	return "unknown";
 }
 
 static inline const char *nvdimm_cmd_name(unsigned cmd)
 {
-	static const char * const names[] = {
+	static const char * const names[nr__ND_CMD] = {
+		[0] = NULL,
 		[ND_CMD_SMART] = "smart",
 		[ND_CMD_SMART_THRESHOLD] = "smart_thresh",
 		[ND_CMD_DIMM_FLAGS] = "flags",
@@ -156,7 +164,7 @@ static inline const char *nvdimm_cmd_name(unsigned cmd)
 		[ND_CMD_CALL] = "cmd_call",
 	};
 
-	if (cmd < ARRAY_SIZE(names) && names[cmd])
+	if (cmd < nr__ND_CMD && names[cmd])
 		return names[cmd];
 	return "unknown";
 }

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[PATCH 10/11] UAPI: ndctl: Remove use of PAGE_SIZE

[David Howells]

The macro PAGE_SIZE isn't valid outside of the kernel, so it should not
appear in UAPI headers.

Furthermore, the actual machine page size could theoretically change from
an application's point of view if it's running in a container that gets
migrated to another machine (say 4K/ppc64 to 64K/ppc64).

Fixes: f2ba5a5baecf ("libnvdimm, namespace: make min namespace size 4K")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Dan Williams <dan.j.williams@intel.com>
cc: linux-nvdimm@lists.01.org
---

 include/linux/ndctl.h      |   22 ++++++++++++++++++++++
 include/uapi/linux/ndctl.h |    4 ----
 2 files changed, 22 insertions(+), 4 deletions(-)
 create mode 100644 include/linux/ndctl.h

diff --git a/include/linux/ndctl.h b/include/linux/ndctl.h
new file mode 100644
index 000000000000..cd5a293ce3ae
--- /dev/null
+++ b/include/linux/ndctl.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2014-2016, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU Lesser General Public License,
+ * version 2.1, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
+ * more details.
+ */
+#ifndef _LINUX_NDCTL_H
+#define _LINUX_NDCTL_H
+
+#include <uapi/linux/ndctl.h>
+
+enum {
+	ND_MIN_NAMESPACE_SIZE = PAGE_SIZE,
+};
+
+#endif /* _LINUX_NDCTL_H */
diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
index 9c89159f6a0f..bcda968e6d80 100644
--- a/include/uapi/linux/ndctl.h
+++ b/include/uapi/linux/ndctl.h
@@ -216,10 +216,6 @@ enum nd_driver_flags {
 	ND_DRIVER_DAX_PMEM	  = 1 << ND_DEVICE_DAX_PMEM,
 };
 
-enum {
-	ND_MIN_NAMESPACE_SIZE = PAGE_SIZE,
-};
-
 enum ars_masks {
 	ARS_STATUS_MASK = 0x0000FFFF,
 	ARS_EXT_STATUS_SHIFT = 16,

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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
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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.
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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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