gst-plugins-bad: avtp: how to notify meson to use custom kernel header

[John Rama]

Thank you Nirbheek for your comment.

> 
> ```
> Command line:  cc -I/usr/src/linux-headers-4.19.0-hoge/include
> /home/makoto/Work/src/gstreamer/gst-build-master/build/meson-private/tmp1wwu5_s0/testfile.c
> -o /home/makoto/Work/src/gstreamer/gst-build-master/build/meson-private/tmp1wwu5_s0/output.obj
> -pipe -
> c -D_FILE_OFFSET_BITS=64 -O0
> 
> Code:
>  #include <linux/net_tstamp.h>
>         void bar(void) {
>             sizeof(struct sock_txtime);
>         };
> Compiler stdout:
> 
> Compiler stderr:
>  /home/makoto/Work/src/gstreamer/gst-build-master/build/meson-private/tmp1wwu5_s0/testfile.c:
> In function 'bar':
> /home/makoto/Work/src/gstreamer/gst-build-master/build/meson-private/tmp1wwu5_s0/testfile.c:3:20:
> error: invalid application of 'sizeof' to incomplete type 'struct
> sock_txtime'
>              sizeof(struct sock_txtime);
>                     ^~~~~~
> 
> Checking for type "struct sock_txtime" : NO
> ```

First of all, my apology.  

There was a typo on specifying the CFLAGS when generating the log file I've attached last mail.
It should be '-I/usr/src/linux-headers-4.19.0-hoge1/include'

Here is the log output with correct CFLAGS.

===================================================
Compiler stderr:
 In file included from /usr/src/linux-headers-4.19.0-hoge1/include/linux/kernel.h:7:0,
                 from /usr/src/linux-headers-4.19.0-hoge1/include/linux/uio.h:12,
                 from /usr/src/linux-headers-4.19.0-hoge1/include/linux/socket.h:8,
                 from /usr/src/linux-headers-4.19.0-hoge1/include/linux/net_tstamp.h:14,
                 from /home/makoto/Work/src/gstreamer/gst-build-master/build3/meson-private/tmp3nzndj9f/testfile.c:1:
/usr/src/linux-headers-4.19.0-hoge1/include/linux/linkage.h:8:25: fatal error: asm/linkage.h: No such file or directory
 #include <asm/linkage.h>
                         ^
compilation terminated.

===================================================

With this log info, I realized I should not use kernel header to build the user space app, but should use libc header.

So, in summary, I could build avtp plugin with following steps.(I'm using debian stretch)

----------------------------------------------------------------------------------
(Assuming that your kernel source tree has the version of 4.19.)
1. create linux-libc-dev packge
   $make deb-pkg LOCALVERSION=-hoge1  -j10
   This will generate linux-libc-dev_4.19.0-hoge1-3_amd64.deb as well as other packages including kernel image and kernel header.
2. install linux-libc-dev package
   sudo  dpkg -x linux-libc-dev_4.19.0-hoge1-3_amd64.deb /usr/src/linux-libc-dev_4.19.0-hoge1-3/
3. linux/net_tstamp.h of kernel 4.19 has bug. Fix it. 
   https://patchwork.ozlabs.org/project/buildroot/patch/20181129214730.7225-1-fontaine.fabrice@gmail.com/
   -	clockid_t	clockid;	/* reference clockid */
   +	__kernel_clockid_t	clockid;/* reference clockid */
4. run meson
  CFLAGS='-I/usr/src/linux-libc-dev_4.19.0-hoge1-3/usr/include/' meson build
----------------------------------------------------------------------------------

Thanks for everyone for the help. I'm glad to close this thread.

John