Re: [PATCH v2] net: fix multicast support with BSD (macOS) socket implementations

[Vitaly Cheptsov]

Hi Jason,

This patch fixes socket communication with QEMU -> host and QEMU <--> QEMU on 
macOS, which was originally impossible due to QEMU and host program having to 
bind to the same ip/port in a way not supported by BSD sockets. The change was 
tested on both Linux and macOS.

Basically after applying this patch one will be able to communicate with QEMU 
when using "-nic socket,mcast=230.0.0.1:1234,model=virtio-net-pci" from QEMU or 
macOS itself.

Best regards,
Vitaly

> On 31 May 2022, at 10:02, Jason Wang <jasowang@redhat.com> wrote:
> 
> On Wed, May 18, 2022 at 3:40 PM Vitaly Cheptsov <cheptsov@ispras.ru> wrote:
>> 
> 
> Hi Vitaly:
> 
> We need a changelog to describe why we need this.
> 
> Thanks
> 
>> Cc: Jason Wang <jasowang@redhat.com>
>> Cc: Daniel P. Berrange <berrange@redhat.com>
>> Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> Signed-off-by: Vitaly Cheptsov <cheptsov@ispras.ru>
>> ---
>> net/socket.c | 18 ++++++++++++++++++
>> 1 file changed, 18 insertions(+)
>> 
>> diff --git a/net/socket.c b/net/socket.c
>> index bfd8596250..583f788a22 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -239,6 +239,22 @@ static int net_socket_mcast_create(struct sockaddr_in 
>> *mcastaddr,
>>         return -1;
>>     }
>> 
>> +#ifdef __APPLE__
>> +    val = 1;
>> +    ret = qemu_setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &val, sizeof(val));
>> +    if (ret < 0) {
>> +        error_setg_errno(errp, errno,
>> +                         "can't set socket option SO_REUSEPORT");
>> +        goto fail;
>> +    }
>> +
>> +    struct sockaddr_in bindaddr;
>> +    memset(&bindaddr, 0, sizeof(bindaddr));
>> +    bindaddr.sin_family = AF_INET;
>> +    bindaddr.sin_addr.s_addr = htonl(INADDR_ANY);
>> +    bindaddr.sin_port = mcastaddr->sin_port;
>> +    ret = bind(fd, (struct sockaddr *)&bindaddr, sizeof(bindaddr));
>> +#else
>>     /* Allow multiple sockets to bind the same multicast ip and port by 
>> setting
>>      * SO_REUSEADDR. This is the only situation where SO_REUSEADDR should be 
>> set
>>      * on windows. Use socket_set_fast_reuse otherwise as it sets 
>> SO_REUSEADDR
>> @@ -253,6 +269,8 @@ static int net_socket_mcast_create(struct sockaddr_in 
>> *mcastaddr,
>>     }
>> 
>>     ret = bind(fd, (struct sockaddr *)mcastaddr, sizeof(*mcastaddr));
>> +#endif
>> +
>>     if (ret < 0) {
>>         error_setg_errno(errp, errno, "can't bind ip=%s to socket",
>>                          inet_ntoa(mcastaddr->sin_addr));
>> --
>> 2.32.1 (Apple Git-133)
>> 
>