The simplest libgfapi example.

hellogluster.c

#include <glusterfs/api/glfs.h>

int main (int argc, char** argv) {
        glfs_t *fs = NULL;
        glfs_fd_t *fd = NULL;
	int ret;
	char *filename = "filename";

	fs = glfs_new ("volume_name");
	ret = glfs_set_volfile_server (fs, "tcp", "server_address", 24007);
	ret = glfs_init (fs);
	fd = glfs_creat (fs, filename, O_RDWR, 0644);
	ret = glfs_write (fd, "hello gluster\n", 15, 0);
	glfs_close (fd);
	return 0;
}

/*
 # rpm -qa | grep glusterfs-api
 glusterfs-api-devel-3.4.1-3.el6.x86_64
 glusterfs-api-3.4.1-3.el6.x86_64
 # gcc hellogluster.c -lgfapi 
*/

Ruby FFI version https://gist.github.com/maebashi/7702150