Update struct on memory read

gistfile1.txt

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

#include <sys/mman.h>
#include <sys/ptrace.h>

struct region
{
	int count;
	char buf[10000];
	int id;
};

int main ( int argc, char *argv[] )
{
	struct sigaction act;
	struct region *rptr;
	pid_t child;
	int fd;

	fd = shm_open("/myregion", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
	if (ftruncate(fd, 0) == -1) return -1;
	rptr = mmap(NULL, sizeof(struct region), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if (rptr == MAP_FAILED) return -1;

	child = fork();
	if(child == 0)
	{
		ptrace(PTRACE_TRACEME, 0, NULL, NULL);
		fprintf(stderr, "rptr: %d\n", rptr->count);
		fprintf(stderr, "rptr: %d\n", rptr->count);
		fprintf(stderr, "rptr: %d %s\n", rptr->count, rptr->buf);
		fprintf(stderr, "rptr: %d %s\n", rptr->count, rptr->buf);
		fprintf(stderr, "rptr: %d\n", rptr->count);
		fprintf(stderr, "rptr: %d 0x%x\n", rptr->count, rptr->id);
		fprintf(stderr, "rptr: %d\n", rptr->count);
	}
	else
	{
		struct region mydata = { 0, "test tmp", 0xdeadbeef };
		int status = ~0;
		size_t i;

		while(!WIFEXITED(status))
		{
			if(!WIFSTOPPED(status) || WSTOPSIG(status) != SIGBUS)
			{
				ptrace(PTRACE_CONT, child, NULL, NULL);
				wait(&status);
				continue;
			}

			mydata.count++;
			lseek(fd, 0, SEEK_SET);
			write(fd, &mydata, sizeof(mydata));
			ptrace(PTRACE_SINGLESTEP, child, NULL, NULL);
			wait(&status);
			if (ftruncate(fd, 0) == -1) return -1;

			ptrace(PTRACE_CONT, child, NULL, NULL);
			wait(&status);
		}
	}

	shm_unlink("/myregion");

	return 0;
}