Re: [PATCH] samples: kdbus: build kdbus-workers conditionally

[Daniel Mack]

Hi Andrew,

On 04/01/2015 11:41 PM, Andrew Morton wrote:
> On Wed, 1 Apr 2015 14:47:20 +0200 Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> 
>> On Tue, Mar 31, 2015 at 03:11:34PM +0200, Daniel Mack wrote:
>>> Give the kdbus sample its own config switch and only build it if it's
>>> explicitly switched on.
>>>
>>> Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx>
>>> Reviewed-by: David Herrmann <dh.herrmann@xxxxxxxxx>
>>> Reported-by: Jiri Slaby <jslaby@xxxxxxx>
>>> ---
>>>  samples/Kconfig        | 7 +++++++
>>>  samples/kdbus/Makefile | 2 +-
>>>  2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> Now applied, thanks.
> 
> Is this going to fix i386 allmodconfig, currently unhappy on my Fedora
> Core 6 (lol) machine?

As allmodconfig will select CONFIG_SAMPLE_KDBUS just as it selected
CONFIG_SAMPLES, that won't help, no.

> samples/kdbus/kdbus-workers.c:73:26: error: sys/signalfd.h: No such file or directory
> samples/kdbus/kdbus-workers.c: In function 'master_new':
> samples/kdbus/kdbus-workers.c:231: warning: implicit declaration of function 'signalfd'
> samples/kdbus/kdbus-workers.c:231: error: 'SFD_CLOEXEC' undeclared (first use in this function)
> samples/kdbus/kdbus-workers.c:231: error: (Each undeclared identifier is reported only once
> samples/kdbus/kdbus-workers.c:231: error: for each function it appears in.)
> samples/kdbus/kdbus-workers.c: In function 'master_handle_signal':
> samples/kdbus/kdbus-workers.c:406: error: storage size of 'val' isn't known
> samples/kdbus/kdbus-workers.c:406: warning: unused variable 'val'
> samples/kdbus/kdbus-workers.c: In function 'child_run':
> samples/kdbus/kdbus-workers.c:773: error: 'CLOCK_MONOTONIC_COARSE' undeclared (first use in this function)
> samples/kdbus/kdbus-workers.c: In function 'bus_open_connection':
> samples/kdbus/kdbus-workers.c:1038: error: 'O_CLOEXEC' undeclared (first use in this function)
> samples/kdbus/kdbus-workers.c: In function 'bus_make':
> samples/kdbus/kdbus-workers.c:1275: error: 'O_CLOEXEC' undeclared (first use in this function)

Hmm, so your libc headers lack support for signalfds, which were
introduced in kernel v2.6.22 (2007), one year after the release of your
distribution.

We can't probe for the existance of files in the local toolchain before
compilation with kdbuild, so we have to stub out the code for glibc
version that are known to lack features. This isn't particularly nice,
but it should work.

Does the attached patch work for you?



Thanks,
Daniel

From 37871360c096b68928750903ac29968a7932e873 Mon Sep 17 00:00:00 2001
From: Daniel Mack <daniel@xxxxxxxxxx>
Date: Fri, 3 Apr 2015 12:41:52 +0200
Subject: [PATCH] samples: kdbus: stub out code for glibc < 2.7

Andrew Morton reports the following build error in samples/kdbus on Fedora
Core 6:

  samples/kdbus/kdbus-workers.c:73:26: error: sys/signalfd.h: No such file or directory
  samples/kdbus/kdbus-workers.c: In function 'master_new':
  samples/kdbus/kdbus-workers.c:231: warning: implicit declaration of function 'signalfd'
  samples/kdbus/kdbus-workers.c:231: error: 'SFD_CLOEXEC' undeclared (first use in this function)
  samples/kdbus/kdbus-workers.c:231: error: (Each undeclared identifier is reported only once
  samples/kdbus/kdbus-workers.c:231: error: for each function it appears in.)
  samples/kdbus/kdbus-workers.c: In function 'master_handle_signal':
  samples/kdbus/kdbus-workers.c:406: error: storage size of 'val' isn't known
  samples/kdbus/kdbus-workers.c:406: warning: unused variable 'val'
  samples/kdbus/kdbus-workers.c: In function 'child_run':
  samples/kdbus/kdbus-workers.c:773: error: 'CLOCK_MONOTONIC_COARSE' undeclared (first use in this function)
  samples/kdbus/kdbus-workers.c: In function 'bus_open_connection':
  samples/kdbus/kdbus-workers.c:1038: error: 'O_CLOEXEC' undeclared (first use in this function)
  samples/kdbus/kdbus-workers.c: In function 'bus_make':
  samples/kdbus/kdbus-workers.c:1275: error: 'O_CLOEXEC' undeclared (first use in this function)

Fedora Core 6 was released in 2006, which predates the introduction of
signalfds in the kernel (v2.6.22, 2007).

The example cannot be built without signalfds, and kbuild cannot depend on
specific features of the local libc when building userspace executables, so
we have to work around the issue by checking for specific glibc versions at
compile time and stub the entire thing if it can't be compiled.

Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx>
Reported-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 samples/kdbus/kdbus-workers.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/samples/kdbus/kdbus-workers.c b/samples/kdbus/kdbus-workers.c
index d1d8f7a..e9ecec8 100644
--- a/samples/kdbus/kdbus-workers.c
+++ b/samples/kdbus/kdbus-workers.c
@@ -57,6 +57,12 @@
  * top-down, but requires some forward-declarations. Just ignore those.
  */
 
+#include <stdio.h>
+#include <stdlib.h>
+
+/* glibc < 2.7 does not ship sys/signalfd.h */
+#if __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 7
+
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -65,8 +71,6 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <sys/poll.h>
@@ -1324,3 +1328,18 @@ static int bus_make(uid_t uid, const char *name)
 
 	return fd;
 }
+
+#else
+
+#warning "Skipping compilation due to unsupported libc version"
+
+int main(int argc, char **argv)
+{
+	fprintf(stderr,
+		"Compilation of %s was skipped due to unsupported libc.\n",
+		argv[0]);
+
+	return EXIT_FAILURE;
+}
+
+#endif /* libc sanity check */
-- 
2.3.4