lib/libgenl.c

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * libgenl.c    GENL library
   4  */
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <unistd.h>
   9
  10 #include <linux/genetlink.h>
  11 #include "libgenl.h"
  12
  13 static int genl_parse_getfamily(struct nlmsghdr *nlh)
  14 {
  15         struct rtattr *tb[CTRL_ATTR_MAX + 1];
  16         struct genlmsghdr *ghdr = NLMSG_DATA(nlh);
  17         int len = nlh->nlmsg_len;
  18         struct rtattr *attrs;
  19
  20         if (nlh->nlmsg_type != GENL_ID_CTRL) {
  21                 fprintf(stderr, "Not a controller message, nlmsg_len=%d "
  22                         "nlmsg_type=0x%x\n", nlh->nlmsg_len, nlh->nlmsg_type);
  23                 return -1;
  24         }
  25
  26         len -= NLMSG_LENGTH(GENL_HDRLEN);
  27
  28         if (len < 0) {
  29                 fprintf(stderr, "wrong controller message len %d\n", len);
  30                 return -1;
  31         }
  32
  33         if (ghdr->cmd != CTRL_CMD_NEWFAMILY) {
  34                 fprintf(stderr, "Unknown controller command %d\n", ghdr->cmd);
  35                 return -1;
  36         }
  37
  38         attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN);
  39         parse_rtattr(tb, CTRL_ATTR_MAX, attrs, len);
  40
  41         if (tb[CTRL_ATTR_FAMILY_ID] == NULL) {
  42                 fprintf(stderr, "Missing family id TLV\n");
  43                 return -1;
  44         }
  45
  46         return rta_getattr_u16(tb[CTRL_ATTR_FAMILY_ID]);
  47 }
  48
  49 int genl_resolve_family(struct rtnl_handle *grth, const char *family)
  50 {
  51         GENL_REQUEST(req, 1024, GENL_ID_CTRL, 0, 0, CTRL_CMD_GETFAMILY,
  52                      NLM_F_REQUEST);
  53         struct nlmsghdr *answer;
  54         int fnum;
  55
  56         addattr_l(&req.n, sizeof(req), CTRL_ATTR_FAMILY_NAME,
  57                   family, strlen(family) + 1);
  58
  59         if (rtnl_talk(grth, &req.n, &answer) < 0) {
  60                 fprintf(stderr, "Error talking to the kernel\n");
  61                 return -2;
  62         }
  63
  64         fnum = genl_parse_getfamily(answer);
  65         free(answer);
  66
  67         return fnum;
  68 }
  69
  70 int genl_init_handle(struct rtnl_handle *grth, const char *family,
  71                      int *genl_family)
  72 {
  73         if (*genl_family >= 0)
  74                 return 0;
  75
  76         if (rtnl_open_byproto(grth, 0, NETLINK_GENERIC) < 0) {
  77                 fprintf(stderr, "Cannot open generic netlink socket\n");
  78                 return -1;
  79         }
  80
  81         *genl_family = genl_resolve_family(grth, family);
  82         if (*genl_family < 0)
  83                 return -1;
  84
  85         return 0;
  86 }