On Fri, Jan 31, 2025 at 10:09:19AM +0100, Stefano Brivio wrote:Fixed, finally. Some answers: On Fri, 31 Jan 2025 17:14:18 +1100 David Gibson <david(a)gibson.dropbear.id.au> wrote:Ok.On Fri, Jan 31, 2025 at 06:36:55AM +0100, Stefano Brivio wrote:It is.On Thu, 30 Jan 2025 09:32:36 +0100 Stefano Brivio <sbrivio(a)redhat.com> wrote:So, I was wondering if binding to 0.0.0.0 is sufficient for a repaired socket.I would like to quickly complete the whole flow first, because I think we can inform design and implementation decisions much better at that pointSo, there seems to be a problem with (testing?) this. I couldn't quite understand the root cause yet, and it doesn't happen with the reference source.c and target.c implementations I shared. Let's assume I have a connection in the source guest to 127.0.0.1:9091, from 127.0.0.1:56350. After the migration, in the target, I get: --- socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 79 setsockopt(79, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 bind(79, {sa_family=AF_INET, sin_port=htons(56350), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 sendmsg(72, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\1", iov_len=1}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[79]}], msg_controllen=24, msg_flags=0}, 0) = 1 recvfrom(72, "\1", 1, 0, NULL, NULL) = 1 setsockopt(79, SOL_TCP, TCP_REPAIR_QUEUE, [2], 4) = 0 setsockopt(79, SOL_TCP, TCP_QUEUE_SEQ, [1788468535], 4) = 0 write(2, "77.6923: ", 977.6923: ) = 9 write(2, "Set send queue sequence for sock"..., 51Set send queue sequence for socket 79 to 1788468535) = 51 write(2, "\n", 1 ) = 1 setsockopt(79, SOL_TCP, TCP_REPAIR_QUEUE, [1], 4) = 0 setsockopt(79, SOL_TCP, TCP_QUEUE_SEQ, [115288604], 4) = 0 write(2, "77.6924: ", 977.6924: ) = 9 write(2, "Set receive queue sequence for s"..., 53Set receive queue sequence for socket 79 to 115288604) = 53 write(2, "\n", 1 ) = 1 connect(79, {sa_family=AF_INET, sin_port=htons(9091), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EADDRNOTAVAIL (Cannot assign requested address) --- EADDRNOTAVAIL, according to the documentation, which seems to be consistent with a glance at the implementation (that is, I must be missing some issue in the kernel), should be returned on connect() if: EADDRNOTAVAIL (Internet domain sockets) The socket referred to by sockfd had not previously been bound to an address and, upon attempting to bind it to an ephemeral port, it was determined that all port numbers in the ephemeral port range are currently in use. See the discussion of /proc/sys/net/ipv4/ip_local_port_range in ip(7). but well, of course it was bound. To a port, indeed, not a full address, that is, any (0.0.0.0) and address port, but I think for the purposes of this description that bind() call is enough.Usually, of course, that 0.0.0.0 would be resolved to a real address at connect() time. But TCP_REPAIR's version of connect() bypasses a bunch of the usual connect logic, so maybe we need an explicit address here.No need.I'm still confused by the specific sequence of events that's causing the problem. If a socket is closed with close(2) it should no longer exist, so I don't see how you could even attempt to do anything with it. Do you mean that the socket is shutdown(RD|WR)? Or that it's been closed by passt, but not by passt-repair? Or the other way around? I'd kind of assume that you _must_ close the socket while still in repair mode, since we want it to go away on the source without attempting to FIN or RST or anything....but that doesn't explain the difference between passt and your test implementation.The difference that actually matters is that the test implementation terminates, and that has the equivalent effect of switching off repair mode for the closed sockets, which frees up all the associated context, including the port. Usually, there are no valid operations on closed sockets (not even close()). This is the first exception I ever met: you can set TCP_REPAIR_OFF.But there's a catch: you can't pass a closed socket in repair mode via SCM_RIGHTS (well, I'm fairly sure nobody approached this level of insanity before): you get EBADF (which is an understatement). And there's another catch: if you actually try to do that, even if it fails, that has the same effect of clearing the socket entirely: you free up the port.!?! this is even more baffling. Passing what's now an unrelated, unassigned integer as an fd is having some effect on a socket that was around!? If so that's a horrifying kernel bug.But we can't use this, unfortunately, because if we do, the peer will get a zero-length read (EOF). Now, I could reintroduce a "quit" command in passt-repair, and we would know that EOF doesn't actually mean completion, but it complicates things again. What works, though, is simply terminating. We can't do that before VHOST_USER_CHECK_DEVICE_STATE, but just after that. That's what I implemented at the moment (updated patches coming soon).-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibsonSame issue in the sense that if I connect namespaces with pasta, I can't migrate a connection between them, because pasta can't migrate a connection. It would close it and try to reopen it.Is this related to SO_REUSEADDR? I need it (on both source and target) because, at least in my tests, source and target are on the same machine, in the same namespace. If I drop it:Again, I can think of various problems that not having the same address available on source and dest might have, but not any which explain the difference between passt and the experimental impl.--- bind(79, {sa_family=AF_INET, sin_port=htons(46280), sin_addr=inet_addr("0.0.0.0")}, 16) = -1 EADDRINUSE (Address already in use) --- as expected. However, in my reference implementation, with a connection from 127.0.0.1:9998 to 127.0.0.1:9091, this is what the target does: --- socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 3 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 bind(3, {sa_family=AF_INET, sin_port=htons(9998), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 socket(AF_UNIX, SOCK_STREAM, 0) = 4 unlink("/tmp/repair.sock") = 0 bind(4, {sa_family=AF_UNIX, sun_path="/tmp/repair.sock"}, 110) = 0 listen(4, 1) = 0 accept(4, NULL, NULL) = 5 sendmsg(5, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\1", iov_len=1}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[3]}], msg_controllen=24, msg_flags=0}, 0) = 1 recvfrom(5, "\1", 1, 0, NULL, NULL) = 1 setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [2], 4) = 0 setsockopt(3, SOL_TCP, TCP_QUEUE_SEQ, [1612504019], 4) = 0 setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [1], 4) = 0 setsockopt(3, SOL_TCP, TCP_QUEUE_SEQ, [1756508956], 4) = 0 connect(3, {sa_family=AF_INET, sin_port=htons(9091), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 --- The only obvious difference is that, here, I'm not binding to an ephemeral port: the source port (in both source and target "guests") is 9998. Fine, so I tried forcing a lower port in passt (source) as well, and this is what I get in the target now: --- socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 79 setsockopt(79, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 bind(79, {sa_family=AF_INET, sin_port=htons(9000), sin_addr=inet_addr("0.0.0.0")}, 16) = 0 sendmsg(72, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\1", iov_len=1}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[79]}], msg_controllen=24, msg_flags=0}, 0) = 1 recvfrom(72, "\1", 1, 0, NULL, NULL) = 1 setsockopt(79, SOL_TCP, TCP_REPAIR_QUEUE, [2], 4) = 0 setsockopt(79, SOL_TCP, TCP_QUEUE_SEQ, [-348109334], 4) = 0 write(2, "46.9751: ", 946.9751: ) = 9 write(2, "Set send queue sequence for sock"..., 51Set send queue sequence for socket 79 to 3946857962) = 51 write(2, "\n", 1 ) = 1 setsockopt(79, SOL_TCP, TCP_REPAIR_QUEUE, [1], 4) = 0 setsockopt(79, SOL_TCP, TCP_QUEUE_SEQ, [-1820322671], 4) = 0 write(2, "46.9752: ", 946.9752: ) = 9 write(2, "Set receive queue sequence for s"..., 54Set receive queue sequence for socket 79 to 2474644625) = 54 write(2, "\n", 1 ) = 1 connect(79, {sa_family=AF_INET, sin_port=htons(9091), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EADDRNOTAVAIL (Cannot assign requested address) --- no obvious difference. I'll try binding to an explicit address, next, but I have no idea why 1. we get EADDRNOTAVAIL after a bind() and 2. it works with the reference implementation.I have no ideas yet :(.Yes, I explicitly close() the socket in the source passt now, but that doesn't change things. This is presumably just an issue with testing, because in real use cases source and target guests would be on different machines. Another idea could be separating the namespaces.Well, if that's relevant to the problem which isn't clear yet. I mean, I guess it's worth trying with source and dest in different namespaces.I can't just run source and target passt in two instances of pasta --config-net, because pasta would run into the same issue,Uh.. which same issue? pasta's not trying to do any TCP_REPAIR stuff or migration.Eh, yes, but we're back to the original problem. A veth interface wouldn't care, instead. Anyway, no need, it's finally working now.but I could isolate one namespace with it, then add two network namespaces inside that, and connect them with veth pairs.Two pasta instances actually sounds like a better bet to me, because the two "hosts" will have the same address, which is what we'd expect for a "real" migration - and it kind of has to be the case for the host side connections to work afterwards.