Sharing VCSM buffers cross-process

p1.c

#include <string.h>                                                                                      
#include <stdio.h>                                                                                       
                                                                                                         
#include <interface/vcsm/user-vcsm.h>                                                                    
                                                                                                         
int main(int argc, char *argv[])
{
        int ret;

        vcsm_init();

        int hnd = vcsm_malloc(4096, "Process 1");
        if (hnd == 0) {
                printf("Alloc failed %d\n", hnd);
        }
        printf("Allocated handle %d\n", hnd);

        char *p = vcsm_lock(hnd);
        if (!p) {
                printf("Map failed\n");
        }
        printf("Mapped at %p\n", p);

        memset(p, 0, 4096);

        sprintf(p, "This is a message in handle %d\n", hnd);

        ret = vcsm_unlock_ptr(p);
        if (ret != 0) {
                printf("Unlock failed %d\n", ret);
        }

        printf("Now run p2, press a key, and enter...\n");
        getchar();
  
        p = vcsm_lock(hnd);
        if (!p) {
                printf("Map failed\n");
        }

        printf("Mapped at %p\n", p);

        printf("Buffer contains:\n%s\n", p);

        ret = vcsm_unlock_ptr(p);
        if (ret != 0) {
                printf("Unlock failed %d\n", ret);
        }

        vcsm_free(hnd);

        vcsm_exit();

        return 0;
}

p2.c

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include <interface/vcsm/user-vcsm.h>

int main(int argc, char *argv[])
{
        int ret;

        if (argc != 2) {
                printf("Usage: %s handle\n", argv[0]);
                printf("\t Import VCSM handle 'handle'\n");
                return 1;
        }

        vcsm_init();

        int hnd = atoi(argv[1]);
        printf("Importing handle %d\n", hnd);

        int shared = vcsm_malloc_share(hnd);
        printf("Imported as handle %d\n", shared);

        char *p = vcsm_lock(shared);
        if (!p) {
                printf("Map failed\n");
        }
        printf("Mapped at %p\n", p);

        printf("Buffer contains:\n%s\n", p);

        sprintf(p + strlen(p), "And this is a response, via handle %d\n", shared);

        ret = vcsm_unlock_ptr(p);
        if (ret != 0) {
                printf("Unlock failed %d\n", ret);
        }

        vcsm_free(shared);

        vcsm_exit();

        return 0;
}

VCSM sharing

Build the two apps:

```
gcc -L/opt/vc/lib -I/opt/vc/include -o p1 -l vcsm p1.c 
gcc -L/opt/vc/lib -I/opt/vc/include -o p2 -l vcsm p2.c 
```

Run p1, then run p2 in another shell