#define _GNU_SOURCE
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/param.h>
#include "__netlink.h"

struct __netlink_handle {
	int fd;
	unsigned int seq;
	size_t bufsize;
};

struct __netlink_handle *__netlink_open(int type)
{
	struct __netlink_handle *nh;
	int bufsize = getpagesize();
	/* required buffer size is MIN(8192,pagesize)-sizeof(struct skb_shared_info)
	 * the estimate for skb_shared_info size is conservative, but gives enough
	 * space to fit struct __netlink_handle including malloc overhead in one page . */
	if (bufsize > 8192) bufsize = 8192;
	bufsize -= 128;
	nh = malloc(sizeof(struct __netlink_handle) + bufsize);
	if (!nh) return 0;
	nh->fd = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, type);
	if (nh->fd < 0) { free(nh); return 0; }
	nh->seq = 1;
	nh->bufsize = bufsize;
	return nh;
}

void __netlink_close(struct __netlink_handle *nh)
{
	close(nh->fd);
	free(nh);
}

int __netlink_enumerate(struct __netlink_handle *nh, int type, int (*cb)(void *ctx, struct nlmsghdr *h), void *ctx)
{
	struct nlmsghdr *h;
	void *buf = (void*)(nh+1);
	struct {
		struct nlmsghdr nlh;
		struct rtgenmsg g;
	} *req = buf;
	int r, ret = 0;

	memset(req, 0, NETLINK_ALIGN(sizeof(*req)));
	req->nlh.nlmsg_len = sizeof(*req);
	req->nlh.nlmsg_type = type;
	req->nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
	req->nlh.nlmsg_seq = nh->seq++;
	req->g.rtgen_family = AF_UNSPEC;
	r = send(nh->fd, req, sizeof(*req), 0);
	if (r < 0) return r;

	while (1) {
		r = recv(nh->fd, buf, nh->bufsize, MSG_DONTWAIT);
		if (r <= 0) return -1;
		for (h = (struct nlmsghdr*) buf; NLMSG_OK(h, (void*)((uint8_t*)buf+r)); h = NLMSG_NEXT(h)) {
			if (h->nlmsg_type == NLMSG_DONE) return ret;
			if (h->nlmsg_type == NLMSG_ERROR) return -1;
			if (!ret) ret = cb(ctx, h);
		}
	}
}