Gentle ping :) > On 3 May 2022, at 19:10, Vitaly Cheptsov <chept...@ispras.ru> wrote: > > Hi Daniel, > > Thank you for your comment. Socket implementation on all the systems is > rather complicated, and while I am fine to update the patch with better > reasoning, it needs to work on macOS. Given the situation with Windows, I > think we may want to ifdef the change to be macOS-specific. > > Other than that, perhaps, we can come to something better if you give some > ideas what should we try. So far this was the only working combination, > however. If you do not have the hardware, I am can perform these tests for > you. > > To simplify the situation, I attached two minimal python scripts, which > closely resemble QEMU actions, and allow testing bidirectional multicast > sockets. > >> When looking in Google there's a comprehensive looking >> description of SO_REUSEADDR + SO_REUSEPORT across all the >> different OS which insists that SO_REUSEPORT and SO_REUSEADDR >> are functionally equivalent for multicast IP addresses: >> >> https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ >> >> And AFAIK, macOS should behave the same way, which suggests >> this patch is not needed. >> >> Oddly though, I don't find this in the FreeBSD man page - its >> description seems fairly clear that SO_REUSEPORT is needed for >> multicast >> >> [quote] >> SO_REUSEPORT allows completely duplicate bindings by multiple processes >> if they all set SO_REUSEPORT before binding the port. This option >> permits multiple instances of a program to each receive UDP/IP multicast >> or broadcast datagrams destined for the bound port. >> [/quote] > > I also saw this description, and it is possible it is a little outdated. I > can safely (entirely) drop setting SO_REUSEADDR on macOS, but it will not > work without socket.SO_REUSEPORT. This can be easily proven with a.py/b.py. > >> I didn't find a quote about this in the FreeBSD man pages I looked >> at, and it feels dubious to me. If the user gives QEMU a address to >> bind to, we should surely be honouring that, not changing it to >> INADDR_ANY. >> >> If using INADDR_ANY though, thsi could explain the need for >> SO_REUSEPORT, since INADDR_ANY is not a designated mcast address. > > I made this judgement from the following part of ip(4): > >> If the IP_BINDANY option is enabled on a SOCK_STREAM, SOCK_DGRAM or a >> SOCK_RAW socket, one can bind(2) to any address, even one not bound to >> any available network interface in the system. > > > This makes some sense, because if I change a.py and b.py > - to bind to MCAST_GRP instead of “0.0.0.0” > - to not set SO_REUSEPORT > > I get "Can't assign requested address” error at sendto in b.py. Same thing > happens in QEMU. > > Best regards, > Vitaly > > > # a.py > import socket > import struct > import scapy.all as scapy > > MCAST_GRP = '230.0.0.1' > MCAST_PORT = 1234 > MULTICAST_TTL = 2 > MAX_PACKET_SIZE = 65535 > > sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) > sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) > sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1) > sock.bind(("0.0.0.0", MCAST_PORT)) > mreq = struct.pack('4sL', socket.inet_aton(MCAST_GRP), socket.INADDR_ANY) > sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq) > > data, _ = sock.recvfrom(MAX_PACKET_SIZE) > print(data) > sock.sendto(b"message_from_a", (MCAST_GRP, MCAST_PORT)) > > # b.py > import socket > import struct > import scapy.all as scapy > > MCAST_GRP = '230.0.0.1' > MCAST_PORT = 1234 > MULTICAST_TTL = 2 > MAX_PACKET_SIZE = 65535 > > sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0) > sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) > sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1) > sock.bind(("0.0.0.0", MCAST_PORT)) > mreq = struct.pack('4sL', socket.inet_aton(MCAST_GRP), socket.INADDR_ANY) > sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq) > > sock.sendto(b"message_from_b", (MCAST_GRP, MCAST_PORT)) > > data, _ = sock.recvfrom(MAX_PACKET_SIZE) > print(data) > > data, _ = sock.recvfrom(MAX_PACKET_SIZE) > print(data) > > % python3 ./a.py > WARNING: No IPv4 address found on en2 ! > WARNING: No IPv4 address found on en1 ! > WARNING: more No IPv4 address found on p2p0 ! > b'message_from_b' > > % python3 ./b.py > WARNING: No IPv4 address found on en2 ! > WARNING: No IPv4 address found on en1 ! > WARNING: more No IPv4 address found on p2p0 ! > b'message_from_b' > b'message_from_a' > >> On 3 May 2022, at 16:13, Daniel P. Berrangé <berra...@redhat.com> wrote: >> >> On Mon, May 02, 2022 at 03:38:30AM +0300, Vitaly Cheptsov wrote: >>> This patch fixes socket communication with QEMU -> host 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. >>> >>> As per BSD manual pages SO_REUSEPORT allows completely duplicate >>> bindings by multiple processes, permitting multiple instances of >>> a program to each receive UDP/IP multicast datagrams destined >>> for the bound port. Without this option macOS, unlike Linux, >>> which (ab)uses SO_REUSEADDR for this purpose, will return >>> "Address already in use" on bind(). >> >> >> When looking in Google there's a comprehensive looking >> description of SO_REUSEADDR + SO_REUSEPORT across all the >> different OS which insists that SO_REUSEPORT and SO_REUSEADDR >> are functionally equivalent for multicast IP addresses: >> >> https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ >> >> And AFAIK, macOS should behave the same way, which suggests >> this patch is not needed. >> >> Oddly though, I don't find this in the FreeBSD man page - its >> description seems fairly clear that SO_REUSEPORT is needed for >> multicast >> >> [quote] >> SO_REUSEPORT allows completely duplicate bindings by multiple processes >> if they all set SO_REUSEPORT before binding the port. This option >> permits multiple instances of a program to each receive UDP/IP multicast >> or broadcast datagrams destined for the bound port. >> [/quote] >> >> >>> >>> As per BSD manual pages binding to any address, even one not bound >>> to any available network interface in the system, should be >>> IP_BINDANY. Without binding to INADDR_ANY macOS will return >>> "Can't assign requested address" on send(). >> >> I didn't find a quote about this in the FreeBSD man pages I looked >> at, and it feels dubious to me. If the user gives QEMU a address to >> bind to, we should surely be honouring that, not changing it to >> INADDR_ANY. >> >> If using INADDR_ANY though, thsi could explain the need for >> SO_REUSEPORT, since INADDR_ANY is not a designated mcast address. >> >>> Cc: Jason Wang <jasow...@redhat.com> >>> Cc: Daniel P. Berrange <berra...@redhat.com> >>> Cc: Philippe Mathieu-Daudé <f4...@amsat.org> >>> Signed-off-by: Vitaly Cheptsov <chept...@ispras.ru> >>> --- >>> net/socket.c | 18 ++++++++++++++++-- >>> 1 file changed, 16 insertions(+), 2 deletions(-) >>> >>> diff --git a/net/socket.c b/net/socket.c >>> index ea5220a2eb..8b2c6c4bb8 100644 >>> --- a/net/socket.c >>> +++ b/net/socket.c >>> @@ -252,10 +252,24 @@ static int net_socket_mcast_create(struct sockaddr_in >>> *mcastaddr, >>> goto fail; >>> } >>> >>> - ret = bind(fd, (struct sockaddr *)mcastaddr, sizeof(*mcastaddr)); >>> + 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; >>> + } >> >> AFAIK, this likely won't compile on Windows since it lacks SO_REUSEPORT >> >>> + >>> + 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)); >>> + >>> if (ret < 0) { >>> error_setg_errno(errp, errno, "can't bind ip=%s to socket", >>> - inet_ntoa(mcastaddr->sin_addr)); >>> + inet_ntoa(bindaddr.sin_addr)); >>> goto fail; >>> } >> >> >> With regards, >> Daniel >> -- >> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| >> |: https://libvirt.org -o- https://fstop138.berrange.com :| >> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >
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