Routing-Table-Manager/app/shm_ip.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/shm.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>

#include "routing-table.h"

/*
* Stores IP address in newly created shared memory region
* corresponding to its key, which is a MAC address. Returns
* the size of created shm on success otherwise -1 on failure.
*/

int store_IP(const char* mac, const char* ip) {

	size_t size = strlen(ip); // account for terminating null byte

	int shm_fd = shm_open(mac, O_CREAT | O_RDWR | O_TRUNC, 0660);

	if (shm_fd == -1) {
		printf("Could not create shared memory for MAC %s - IP %s pair\n",
			mac,
			ip);
		return -1;
	}

	if (ftruncate(shm_fd, size) == -1) {
		printf("Error on ftruncate to allocate size for IP %s\n", ip);
		return -1;
	}

	void* shm_reg = mmap(NULL,
		size,
		PROT_READ | PROT_WRITE,
		MAP_SHARED,
		shm_fd,
		0);

	if (shm_reg == MAP_FAILED) {
		printf("Mapping failed\n");
		return -1;
	}

	memset(shm_reg, 0, size);
	memcpy(shm_reg, ip, size);

	if (munmap(shm_reg, size) == -1) {
		printf("Unmapping failed\n");
		return -1;
	}

	close(shm_fd);
	return size;
}

/*
* Get the IP address corresponding to the MAC address
* from the shared region that the server created.
* Returns number of bytes on success else -1 on
* failure.
*/

int get_IP(const char* mac, char* ip) {

	int shm_fd = shm_open(mac,
		O_CREAT | O_RDONLY,
		0660);

	if (shm_fd == -1) {
		printf("Couldn't open shared memory for MAC %s - IP %s pair\n",
			mac,
			ip);
		return -1;
	}

	void* shm_reg = mmap(NULL,
		IP_ADDR_LEN,
		PROT_READ,
		MAP_SHARED,
		shm_fd,
		0);

	if (shm_reg == MAP_FAILED) {
		printf("Mapping failed\n");
		return -1;
	}

	memcpy(ip, shm_reg, IP_ADDR_LEN);
	if (munmap(shm_reg, IP_ADDR_LEN) == -1) {
		printf("Unmapping failed\n");
		return -1;
	}

	close(shm_fd);
	return strlen(ip);
}