Net::Interface::Developer(3) api, notes, hints


This contains development notes and API documentation for the Net::Interface module. It is hoped that others will help fill in the missing pieces for OS's and address families that are currently unsupported.


Net::Interface gathers information about the network interfaces in an OS independent fashion by first attempting to use "getifaddrs" if "getifaddrs" is not supported on the OS it falls back to using system "ioctl's" and the "ifreq, in6_ifreq, lifreq" structures defined on the local host. Linux differs somewhat since ipV6 information is available only directly from the kernel on older versions where "getifaddrs" is not available. The "ifreq" and friends information is used to generate a "getifaddrs" response.

Herein lies the need for continued development by the opensource community. Many OS's have peculiar "ioctl" variants and SIOC's variants that require unique code solutions. I'm sure that all of them are not presently included.

Net::Interface is built in 5 layers, listed below from the base up.

description:      files           code

1) AF_xxx families: ni_af_inetcommon.c     (C)

Code modules for AF families. Currently supported are AF_INET, AF_INET6. There is partial support for AF_LINK and AF_PACKET for retrieval of MAC address from the interface where it is needed. Where the code is reasonably universal for a particular address family and the methods used to retrieve the information from the OS, it resides in an af_xxxx.c file.

2) IFREQ families: ni_xx_ifreq.c   (C)

Code modules for IFREQ families. Currently supported are:
  • "ifreq" ni_ifreq.c

    Provides support for retrieval of ipV4 information. The structure "ifreq" does not provide enough space to return data about socket address families larger than "struct sockaddr". All known operating systems support this flavor of data retrieval. ni_ifreq.c makes use of calls to ni_af_inet.c

  • "in6_ifreq" ni_in6_ifreq.c

    Provides support for retrieval of both ipV4 and ipV6 information. "in6_ifreq" uses "struct sockaddr_storage" rather than the smaller "struct sockaddr" that is used in "ifreq". This code modules support variants of the BSD operating system and a few others. ni_in6_ifreq makes use of calls to ni_af_inetcommon.c

  • "lifreq" ni_lifreq.c

    Provides support for retrieval of both ipV4 and ipV6 information. "lifreq" has a custom format unique to the SUN operating systems. Pretty much everything in it, while similar to the two previous code modules, is custom.

  • "linuxproc" ni_linuxproc.c

    Provides support for retrieval of both ipV4 and ipV6 information. "linuxproc" uses calls to ni_af_inet.c to get ipV4 information int "getifaddrs" format and custom code to collect similarly formatted ipV6 information directly from the /proc file system. It then performs a merge on these two data sets to put them into proper order and add fake AF_LINK or AF_PACKET records to provide "getifaddrs" compatiable access to the MAC address through the returned "struct ifaddrs" array.

3) getifaddrs ni_getifaddrs.c  (C)

The "getifaddrs" code module contains the decision mechanism for how data is retrieved for a particular build of Net::Interface. At build time, portions of the code are #ifdef'd in/out depending on the availabiltiy of resource from the underlying OS. In addition, at run time, if the system does not have native "getifaddrs" then a decision tree is used depending on the response to calls for data to the various code modules described in section 2).

4) Sub-system Interface.xs    (PERLXS)

This file asks for the data about the interfaces with a generic call to "getifaddrs". The data returned resides in memory allocated by the OS and must be freed or a memory leak will result as it is not tracked by Perl's garbage collector. "Interface.xs" moves the interface data from allocated memory to Perl managed memory where it can be reclaimed by the garbage collection mechanism if/when the user space program turns it loose. This eliminates the need for a "close" operation to free the OS's allocated memory.

5) User space      (Perl)


The pure perl portion of this module performs most of the presentation operations for the user that are published in the API for Net::Interface.

        *\  \  \    |    /  /  /*
        *      user space       *
                    ^                                Net::Interface
                    |                           Architecture Block Diagram
        *     *
        *      Interface.xs     *
        *************************               *************************       
        *   system getifaddrs   *               *      ni_getifreqs     *
        *          via          *<-if missing ->*           via         *
        *   (ni_getifaddrer.c)  *               *    (ni_ifreq.c)       *
        *************************               *    (ni_lifreq.c)      *
                                                *    (ni_in6_ifreq.c)   *
                                                *    (ni_linuxproc.c)   *
                                                *  (ni_af_inetcommon.c) *


Access to the pieces of code in the block diagram above are available through a developer API. These codes snippets from Interfaces.xs describe the access.

        SV *ref
        d_ni_ifreq      = NI_IFREQ
        d_ni_lifreq     = NI_LIFREQ
        d_ni_in6_ifreq  = NI_IN6_IFREQ
        d_ni_linuxproc  = NI_LINUXPROC
        char * process;
        int er = ni_developer(ix);


        SV * ref
 #      base            = 0
        gifa_ifreq      = NI_IFREQ
        gifa_lifreq     = NI_LIFREQ
        gifa_in6_ifreq  = NI_IN6_IFREQ
        gifa_linuxproc  = NI_LINUXPROC
        struct ifaddrs * ifap;
        int rv;
        if ((rv = ni_getifaddrs(&ifap,ix)) == -1) {
            printf("failed PUNT!\n");

Both function sets result in a printed description to the terminal window to facilitate code creation and debug. Currently the ref is unused. It is expected that future development will modify or add to function access.

  # for developer
  use strict;
  use Net::Interface;
  # to call OS native getifaddrs if present
  print "\nifreq\n";  gifaddrs_base Net::Interface();
  # to call ni_linuxproc fallback getifaddrs
  print "\nlxp\n";    gifa_linuxproc Net::Interface();
  # to call ni_linuxproc ifreq emulation
  print "\nglxp\n";   d_ni_linuxproc Net::Interface();



If you have gotten this far, it is time to read some of the code. AF_familes and IFREQ_families are accessed through constuctor structs found at the bottom of each of the ni_af_xxx and ni_xx_ifreq source files. Their vectoring components are described in "ni_func.h" near the bottom and in "ni_util.c" in the section labeled constructor registration the essence of which is described here.

  struct ni_ifconf_flavor * ni_ifcf_get(enum ni_FLAVOR type)
  struct ni_ifconf_flavor * ni_safe_ifcf_get(enum ni_FLAVOR type);
  nifp = ni_ifcf_get(NI_IFREQ);

Returns a pointer "nifp" to the structure for a particular flavor of ifreq. If a flavor is unsupported on a particular architecture a NULL is returned by the first invocation and NI_IFREQ by the second. Currently supported flavors are:

  enum ni_FLAVOR {
        NI_NULL,        reserved for the getifaddrs base system call
  struct ni_ifconf_flavor {
    enum ni_FLAVOR              ni_type;
    int                         (*gifaddrs)
    int                         siocgifindex;  
    int                         siocsifaddr;   
    int                         siocgifaddr;   
    int                         siocdifaddr;   
    int                         siocaifaddr;   
    int                         siocsifdstaddr;
    int                         siocgifdstaddr;
    int                         siocsifflags;
    int                         siocgifflags;
    int                         siocsifmtu;
    int                         siocgifmtu;
    int                         siocsifbrdaddr;
    int                         siocgifbrdaddr;
    int                         siocsifnetmask;
    int                         siocgifnetmask;
    int                         siocsifmetric;
    int                         siocgifmetric;
    int                         ifr_offset;
    void                        (*fifaddrs)      howto free ifaddrs
    int                         (*refreshifr)    howto refresh ifreq
    void *                      (*getifreqs)     howto get ifreq
    int                         (*developer)     developer access
    struct ni_ifconf_flavor *   ni_ifcf_next;


NI_PRINT_MAC(u_char * hex_mac_string);
  printf statement for terminal output of the form
NI_MAC_NOT_ZERO(u_char * hex_mac_string)
  if( NI_MAC_NOT_ZERO(macp))
        do something
NI_PRINT_IPV6(struct sin6_addr);
  Takes an agrument of the form sockaddr_in6.sin6_addr and prints


int ni_clos_reopn_dgrm(int fd, int af)
Closes and then opens an "ioctl" socket of type SOCK_DGRAM and returns the socket value. If the socket value is NEGATIVE, no close is attempted an the call is equivalent to:

void ni_gifa_free(struct ifaddrs * ifap, int flavor)
Use the appropriate free memory function call depending on the flavor of the getifaddrs function that returned the ifaddrs structure list.
int nifreq_gifaddrs(struct ifaddrs **ifap, struct ni_ifconf_flavor *nifp)
Our semi-standard version of "getifaddrs" used by OS's that provide "ifreq" and "in6_ifreq".

NOTE: all calls to "getifaddrs" return -1 on failure and and the FLAVOR as enumerated above on success.

  i.e. NI_NULL for the native getifaddrs, NI_IFREQ, NI_LINUXPROC, etc...
uint32_t ni_ipv6addr_gettype(struct in6_addr * in6p)
Extracts information about the type of ipV6 address. The returned value may be passed to the NEXT function call to print.
int ni_lx_map2scope(int lscope)
This function maps Linux style scope bits to their RFC-2373 equivalent.

    scope flags rfc-2373
        0       reserved
        1    node-local (aka loopback, interface-local)
        2    link-local
        3       unassigned
        4       unassigned
        5    site-local
        6       unassigned
        7       unassigned
        8    organization-local
        9       unassigned
        A       unassigned
        B       unassigned
        C       unassigned
        D       unassigned
        E    global scope
        F       reserved
      Linux   rfc-2372                
     0x0000     0xe     GLOBAL
     0x0020u    0x2     LINKLOCAL
     0x0040u    0x5     SITELOCAL
void ni_linux_scope2txt(uint32_t type)
Print information about an ipV6 address for each bit present in "type".

  const ni_iff_t ni_lx_type2txt[] = {
        { IPV6_ADDR_ANY,                "unknown" },
        { IPV6_ADDR_UNICAST,            "unicast" },
        { IPV6_ADDR_MULTICAST,          "multicast" },
        { IPV6_ADDR_ANYCAST,            "anycast" },
        { IPV6_ADDR_LOOPBACK,           "loopback" },
        { IPV6_ADDR_LINKLOCAL,          "link-local" },
        { IPV6_ADDR_SITELOCAL,          "site-local" },
        { IPV6_ADDR_COMPATv4,           "compat-v4" },
        { IPV6_ADDR_SCOPE_MASK,         "scope-mask" },
        { IPV6_ADDR_MAPPED,             "mapped" },
        { IPV6_ADDR_RESERVED,           "reserved" },
        { IPV6_ADDR_ULUA,               "uniq-lcl-unicast" },
        { IPV6_ADDR_6TO4,               "6to4" },
        { IPV6_ADDR_6BONE,              "6bone" },
        { IPV6_ADDR_AGU,                "global-unicast" },
        { IPV6_ADDR_UNSPECIFIED,        "unspecified" },
        { IPV6_ADDR_SOLICITED_NODE,     "solicited-node" },
        { IPV6_ADDR_ISATAP,             "ISATAP" },
        { IPV6_ADDR_PRODUCTIVE,         "productive" },
        { IPV6_ADDR_6TO4_MICROSOFT,     "6to4-ms" },
        { IPV6_ADDR_TEREDO,             "teredo" },
        { IPV6_ADDR_ORCHID,             "orchid" },
        { IPV6_ADDR_NON_ROUTE_DOC,      "non-routeable-doc" }
int ni_sizeof_type2txt()
Returns the size of the above table.
u_int ni_get_scopeid(struct sockaddr_in6 * sin6)
On systems using KAME, this function extracts and returns the scope from field 2 of the ipV6 address and sets fields 2,3 to zero. On all other systems it returns

   scope flags     rfc-2373
        0         reserved
        1       node-local
        2       link-local
        3         unassigned
        4         unassigned
        5       site-local
        6         unassigned
        7         unassigned
        8       organization-local
        9         unassigned
        A         unassigned
        B         unassigned
        C         unassigned
        D         unassigned
        E       global scope
        F         reserved
void * ni_memdup(void *memp, int size)
Allocate memory of for size and copy contents from memp. Returns NULL on error and sets errno to ENOMEM.
void ni_plen2mask(void * in_addr, int plen, int sizeofaddr)
Create a NETMASK string from a prefix length

For ipV4: ni_plen2mask(&in_addr, cidr, sizeof(struct in_addr));

For ipV6: ni_plen2mask(&in6_addr, cidr, sizeof(struct in6_addr));

int ni_prefix(void * ap, int len, int size)
Calculated the prefix length for a NETMASK where *ap points to the binary representation of the NETMASK and size is the number of bytes in the mask.

For ipV4: ni_prefix(&in_addr,sizeof(struct in_addr));

For ipV6: ni_prefix(&in6_addr,sizeof(struct(in6_addr));

int ni_refresh_ifreq(int fd, struct ifconf *ifc, void **oifr, void **olifr, struct ni_ifconf_flavor * nifp)
Some OS lose scope on the particular device/addr handle when certain ioctl's are performed. This function refreshs the ifconf chain and positions the pointers in the exact same spot with fresh scope.

See ni_in6_ifreq.c and ni_af_net6.c for usage. Search for the string refreshifr. Code snippit looks like:



        Copyright 2008-2009 - Michael Robinton

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