使用SWIG / PHP控制Raspberry Pi上的应用程序（mjpg-streamer）

Question

I try to start 'mjpg-streamer' via a swig/c/php interface on a raspberry pi. Previously, two apps are successfully controlled via swig/c/php:

• GPIO-control via i2cset
• GPIO-control via wiringPI

In case of the 'mjpg-streamer', I used the following code:

  void stream(void) { system("export LD_LIBRARY_PATH=/usr/local/lib/"); system("mjpg_streamer -o 'output_http.so -w /media/MINIUSB/dev/Control/www' -i 'input_raspicam.so -x 640 -y 480 -fps 15'"); } 

and run 'make' as in case of the GPIO-controls

    swig -Wextra -php camera.i
    gcc -fpic -c `php-config --includes` camera.c camera_wrap.c
    gcc -shared camera_wrap.o camera.o -o camera.so
    cp camera.so `php-config --extension-dir`
    service lighttpd restart

Finally I run 'chmod 4755 /usr/local/lib/input_raspicam.so' and 'chmod 4755 /usr/local/lib/output_http.so', as I did it to enable 'i2cset' etc.

In this example I do not use /dev/video[0..n], maybe it should be another device.

The system runs under raspbian jessie, php-5.6.14, php5-[dev,cli,cgi], lighttpd, swig-2.0.12. According to phpinfo(), the module was successfully loaded.

Has anyone any idea what's going wrong?

Answer 1

I don't think the two calls to system do what you hope they will do when run consecutively like that. The export of the first call will only impact the environment of the process of the shell spawned for that specific call to system . The next call to system will inherit the environment of its parent, which won't have been changed. Instead what you might want to do is:

system("LD_LIBRARY_PATH=/usr/local/lib/ mjpg_streamer -o 'output_http.so -w /media/MINIUSB/dev/Control/www' -i 'input_raspicam.so -x 640 -y 480 -fps 15'");

Which will set the environment for the process that calls mjpg_streamer. Or better yet use putenv/setenv instead.

Since you're using PHP though and just calling system you'd be better off using PHPs shell_exec or similar since there isn't anything in your C that PHP can't already do (it just calls bash for you in a round about kind of way)

Answer 2

When building your app, you can build the rpath into the .so with gcc -Wl,-rpath,/usr/local/lib ... instead of using LD_LIBRARY_PATH.

As @Flexo noted, a separate system() to set the environment variable won't affect the environment in subsequent calls to system()