DESCRIPTION
The ifmib facility is an application of the sysctl(3) interface to provide management information about network interfaces to client applications such as netstat(1), slstat(8), and SNMP management agents. This information is structured as a table, where each row in the table represents a logical network interface (either a hardware device or a software pseudo-device like lo(4)). There are two columns in the table, each containing a single structure: one column contains generic information relevant to all interfaces, and the other contains information specific to the particular class of interface. (Generally the latter will implement the SNMP MIB defined for that particular interface class, if one exists and can be implemented in the kernel.) The ifmib facility is accessed via the "net.link.generic" branch of the sysctl(3) MIB. The manifest constants for each level in the sysctl(3) name are defined in
.In net/if_mib.h . The index of the last row in the table is given by "net.link.generic.system.ifcount" (or, using the manifest constants, CTL_NET, PF_LINK, NETLINK_GENERIC, IFMIB_SYSTEM, IFMIB_IFCOUNT). A management application searching for a particular interface should start with row 1 and continue through the table row-by-row until the desired interface is found, or the interface count is reached. Note that the table may be sparse, i.e., a given row may not exist, indicated by an errno of ENOENT. Such an error should be ignored, and the next row should be checked.
The generic interface information, common to all interfaces, can be accessed via the following procedure:
int
get_ifmib_general(int row, struct ifmibdata *ifmd)
{
int name[6];
size_t len;
name[0] = CTL_NET;
name[1] = PF_LINK;
name[2] = NETLINK_GENERIC;
name[3] = IFMIB_IFDATA;
name[4] = row;
name[5] = IFDATA_GENERAL;
len = sizeof(*ifmd);
return sysctl(name, 6, ifmd, &len, (void *)0, 0);
}
The fields in struct ifmibdata are as follows:
