Re: [FFmpeg-devel] [PATCH v2.1 2/2] avformat/udp: Select output interfaces for ipv6 multicast

[Michael Niedermayer <michael@niedermayer.cc>]

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Hi Peter

On Fri, Aug 08, 2025 at 09:27:35AM +0200, Peter Enderborg wrote:
> This fixes two old TODO's in ipv6 multicast handling.
> If the system as SIOCGIFINDEX ioctl a helper function to iterate over
> all interfaces added to join the multicast group on interface if approperite.
> 
> The default value is IN6ADDR_ANY (::) and it then joins all interfaces
> that are up and have multicast support. Local address can be
> specified and then it join ALL interfaces that use that specific
> local address.
> 
> Limitations (TODO's)
> Handling when network configuration is changed. if up/down etc.
> 
> Signed-off-by: Peter Enderborg <peterend@axis.com>
> ---
>  libavformat/udp.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 96 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/udp.c b/libavformat/udp.c
> index 84f9d3e62e..a0482c122f 100644
> --- a/libavformat/udp.c
> +++ b/libavformat/udp.c
> @@ -68,6 +68,13 @@
>  #include "libavutil/thread.h"
>  #endif
>  
> +#if HAVE_STRUCT_IPV6_MREQ && HAVE_IOCTL_GIFINDEX && defined(IPPROTO_IPV6)
> +#include <sys/types.h>
> +#include <net/if.h>
> +#include <sys/ioctl.h>
> +#include <ifaddrs.h>
> +#endif
> +
>  #ifndef IPV6_ADD_MEMBERSHIP
>  #define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
>  #define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
> @@ -205,6 +212,79 @@ static int udp_set_multicast_ttl(int sockfd, int mcastTTL,
>  
>      return 0;
>  }
> +#if HAVE_STRUCT_IPV6_MREQ && HAVE_IOCTL_GIFINDEX && defined(IPPROTO_IPV6)
> +static int udp_ipv6_multicast_iterate(int sockfd, struct sockaddr_in6 *addr,
> +                                      struct sockaddr_in6 *local_addr, int mop, void *logctx)
> +{
> +    struct in6_addr anyipv6 = IN6ADDR_ANY_INIT;
> +    struct ifaddrs *ifal=NULL,*ife=NULL;
> +    int iindex_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
> +    int membership_changed = 0;
> +
> +    if (iindex_fd >= 0 && !getifaddrs(&ifal)) {
> +        for(ife=ifal; ife!=NULL; ife=ife->ifa_next) {
> +            if (ife->ifa_addr &&
> +                (ife->ifa_addr->sa_family == AF_INET6) &&
> +                (ife->ifa_flags & IFF_MULTICAST) &&
> +                (ife->ifa_flags & IFF_UP)) {
> +                if ((!memcmp(&local_addr->sin6_addr, &anyipv6, sizeof(struct in6_addr))) ||
> +                    (!memcmp(&local_addr->sin6_addr, &((struct sockaddr_in6 *)ife->ifa_addr)->sin6_addr, sizeof(struct in6_addr)))) {
> +                    struct ifreq if_req;
> +                    strncpy(if_req.ifr_name, ife->ifa_name, IFNAMSIZ);
> +                    if (ioctl(iindex_fd, SIOCGIFINDEX, &if_req) != -1) {
> +                        struct ipv6_mreq mreq6;
> +                        memcpy(&mreq6.ipv6mr_multiaddr, &addr->sin6_addr, sizeof(struct in6_addr));
> +                        mreq6.ipv6mr_interface = if_req.ifr_ifindex;
> +                        switch (mop) {
> +                        case IPV6_JOIN_GROUP:
> +                            if (setsockopt(sockfd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &mreq6, sizeof(mreq6)) == 0) {
> +                                membership_changed = 1;
> +                            } else {
> +                                /* Subscribe for all ipv6 addresses belong to a
> +				   interface.It can generate EADDRINUSE but
> +				   is accaptable. */
> +                                if (errno != EADDRINUSE) {
> +                                    ff_log_net_error(logctx, AV_LOG_ERROR, "setsockopt(IPV6_ADD_MEMBERSHIP)");
> +                                    goto error;

the patch mixes tabs and spaces, we use only spaces in C files for indention.

I will leave the review of teh actual changes to others as I am sure
you know much more about ipv6 multicast than i do

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Does the universe only have a finite lifespan? No, its going to go on
forever, its just that you wont like living in it. -- Hiranya Peiri

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