msg.c revision 64f17e85b4783b1a34f6d46dd8aed2745ed0c583 
1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *	http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/* NOTICE: This is a clean room re-implementation of libnl */
18
19#include <malloc.h>
20#include <unistd.h>
21#include <linux/netlink.h>
22#include "netlink-types.h"
23
24/* Allocate a new netlink message with the default maximum payload size. */
25struct nl_msg *nlmsg_alloc(void)
26{
27	/* Whole page will store nl_msg + nlmsghdr + genlmsghdr + payload */
28	const int page_sz = getpagesize();
29	struct nl_msg *nm;
30	struct nlmsghdr *nlh;
31
32	/* Netlink message */
33	nm = (struct nl_msg *) malloc(page_sz);
34	if (!nm)
35		goto fail;
36
37	/* Netlink message header pointer */
38	nlh = (struct nlmsghdr *) ((char *) nm + sizeof(struct nl_msg));
39
40	/* Initialize */
41	memset(nm, 0, page_sz);
42	nm->nm_size = page_sz;
43
44	nm->nm_src.nl_family = AF_NETLINK;
45	nm->nm_src.nl_pid = getpid();
46
47	nm->nm_dst.nl_family = AF_NETLINK;
48	nm->nm_dst.nl_pid = 0; /* Kernel */
49
50	/* Initialize and add to netlink message */
51	nlh->nlmsg_len = NLMSG_HDRLEN;
52	nm->nm_nlh = nlh;
53
54	/* Add to reference count and return nl_msg */
55	nlmsg_get(nm);
56	return nm;
57fail:
58	return NULL;
59}
60
61/* Return pointer to message payload. */
62void *nlmsg_data(const struct nlmsghdr *nlh)
63{
64	return (char *) nlh + NLMSG_HDRLEN;
65}
66
67/* Add reference count to nl_msg */
68void nlmsg_get(struct nl_msg *nm)
69{
70	nm->nm_refcnt++;
71}
72
73/* Release a reference from an netlink message. */
74void nlmsg_free(struct nl_msg *nm)
75{
76	if (nm) {
77		nm->nm_refcnt--;
78		if (nm->nm_refcnt <= 0)
79			free(nm);
80	}
81
82}
83
84/* Return actual netlink message. */
85struct nlmsghdr *nlmsg_hdr(struct nl_msg *n)
86{
87	return n->nm_nlh;
88}
89
90/* Return head of attributes data / payload section */
91struct nlattr *nlmsg_attrdata(const struct nlmsghdr *nlh, int hdrlen)
92{
93	unsigned char *data = nlmsg_data(nlh);
94	return (struct nlattr *)(data + NLMSG_ALIGN(hdrlen));
95}
96
97/* Returns pointer to end of netlink message */
98void *nlmsg_tail(const struct nlmsghdr *nlh)
99{
100	return (void *)((char *)nlh + NLMSG_ALIGN(nlh->nlmsg_len));
101}
102
103/* Next netlink message in message stream */
104struct nlmsghdr *nlmsg_next(struct nlmsghdr *nlh, int *remaining)
105{
106	struct nlmsghdr *next_nlh = NULL;
107	int len = nlmsg_len(nlh);
108
109	len = NLMSG_ALIGN(len);
110	if (*remaining > 0 &&
111	    len <= *remaining &&
112	    len >= (int) sizeof(struct nlmsghdr)) {
113		next_nlh = (struct nlmsghdr *)((char *)nlh + len);
114		*remaining -= len;
115	}
116
117	return next_nlh;
118}
119
120int nlmsg_datalen(const struct nlmsghdr *nlh)
121{
122	return nlh->nlmsg_len - NLMSG_HDRLEN;
123}
124
125/* Length of attributes data */
126int nlmsg_attrlen(const struct nlmsghdr *nlh, int hdrlen)
127{
128	return nlmsg_datalen(nlh) - NLMSG_ALIGN(hdrlen);
129}
130
131/* Length of netlink message */
132int nlmsg_len(const struct nlmsghdr *nlh)
133{
134	return nlh->nlmsg_len;
135}
136
137/* Check if the netlink message fits into the remaining bytes */
138int nlmsg_ok(const struct nlmsghdr *nlh, int rem)
139{
140	return rem >= (int)sizeof(struct nlmsghdr) &&
141		rem >= nlmsg_len(nlh) &&
142		nlmsg_len(nlh) >= (int) sizeof(struct nlmsghdr) &&
143		nlmsg_len(nlh) <= (rem);
144}
145
146int nlmsg_padlen(int payload)
147{
148	return NLMSG_ALIGN(payload) - payload;
149}
150