For now, the tcp socket lookup will terminate if the socket is reuse port
in inet_lhash2_lookup(), which makes the socket is not the best match.

For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
but socket1 bind on "eth0". We create socket1 first, and then socket2.
Then, all connections will goto socket2, which is not expected, as socket1
has higher priority.

This can cause unexpected behavior if TCP MD5 keys is used, as described
in Documentation/networking/vrf.rst -> Applications.

Therefor, we lookup the best matched socket first, and then do the reuse
port logic. This can increase some overhead if there are many reuse port
socket :/

Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
v3:
* use the approach in V1
* add the Fixes tag
---
 net/ipv4/inet_hashtables.c  | 13 +++++++------
 net/ipv6/inet6_hashtables.c | 13 +++++++------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ceeeec9b7290..51751337f394 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
 	sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
 		score = compute_score(sk, net, hnum, daddr, dif, sdif);
 		if (score > hiscore) {
-			result = inet_lookup_reuseport(net, sk, skb, doff,
-						       saddr, sport, daddr, hnum, inet_ehashfn);
-			if (result)
-				return result;
-
 			result = sk;
 			hiscore = score;
 		}
 	}
 
-	return result;
+	if (!result)
+		return NULL;
+
+	sk = inet_lookup_reuseport(net, result, skb, doff,
+				   saddr, sport, daddr, hnum, inet_ehashfn);
+
+	return sk ? sk : result;
 }
 
 struct sock *inet_lookup_run_sk_lookup(const struct net *net,
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 76ee521189eb..2554f26d6c20 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -161,17 +161,18 @@ static struct sock *inet6_lhash2_lookup(const struct net *net,
 	sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
 		score = compute_score(sk, net, hnum, daddr, dif, sdif);
 		if (score > hiscore) {
-			result = inet6_lookup_reuseport(net, sk, skb, doff,
-							saddr, sport, daddr, hnum, inet6_ehashfn);
-			if (result)
-				return result;
-
 			result = sk;
 			hiscore = score;
 		}
 	}
 
-	return result;
+	if (!result)
+		return NULL;
+
+	sk = inet6_lookup_reuseport(net, result, skb, doff,
+				    saddr, sport, daddr, hnum, inet6_ehashfn);
+
+	return sk ? sk : result;
 }
 
 struct sock *inet6_lookup_run_sk_lookup(const struct net *net,
-- 
2.50.1

Hi Menglong,

On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> For now, the tcp socket lookup will terminate if the socket is reuse port
> in inet_lhash2_lookup(), which makes the socket is not the best match.
>
> For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> but socket1 bind on "eth0". We create socket1 first, and then socket2.
> Then, all connections will goto socket2, which is not expected, as socket1
> has higher priority.
>
> This can cause unexpected behavior if TCP MD5 keys is used, as described
> in Documentation/networking/vrf.rst -> Applications.
>
> Therefor, we lookup the best matched socket first, and then do the reuse

s/Therefor/Therefore

> port logic. This can increase some overhead if there are many reuse port
> socket :/
>
> Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---
> v3:
> * use the approach in V1
> * add the Fixes tag
> ---
>  net/ipv4/inet_hashtables.c  | 13 +++++++------
>  net/ipv6/inet6_hashtables.c | 13 +++++++------
>  2 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index ceeeec9b7290..51751337f394 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
>         sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
>                 score = compute_score(sk, net, hnum, daddr, dif, sdif);
>                 if (score > hiscore) {
> -                       result = inet_lookup_reuseport(net, sk, skb, doff,
> -                                                      saddr, sport, daddr, hnum, inet_ehashfn);
> -                       if (result)
> -                               return result;
> -
>                         result = sk;
>                         hiscore = score;
>                 }
>         }
>
> -       return result;
> +       if (!result)
> +               return NULL;
> +
> +       sk = inet_lookup_reuseport(net, result, skb, doff,
> +                                  saddr, sport, daddr, hnum, inet_ehashfn);
> +
> +       return sk ? sk : result;
>  }

IMHO, I don't see it as a bugfix. So can you elaborate on what the exact
side effect you're faced with is when the algorithm finally prefers
socket2 (without
this patch)?

AFAIK, the current approach breaks the initial design and might make
the whole lookup process take a longer time in certain cases like you mentioned.

Thanks,
Jason

On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
>
> Hi Menglong,
>
> On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> >
> > For now, the tcp socket lookup will terminate if the socket is reuse port
> > in inet_lhash2_lookup(), which makes the socket is not the best match.
> >
> > For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> > but socket1 bind on "eth0". We create socket1 first, and then socket2.
> > Then, all connections will goto socket2, which is not expected, as socket1
> > has higher priority.
> >
> > This can cause unexpected behavior if TCP MD5 keys is used, as described
> > in Documentation/networking/vrf.rst -> Applications.
> >
> > Therefor, we lookup the best matched socket first, and then do the reuse
>
> s/Therefor/Therefore
>
> > port logic. This can increase some overhead if there are many reuse port
> > socket :/
> >
> > Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
> > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > ---
> > v3:
> > * use the approach in V1
> > * add the Fixes tag
> > ---
> >  net/ipv4/inet_hashtables.c  | 13 +++++++------
> >  net/ipv6/inet6_hashtables.c | 13 +++++++------
> >  2 files changed, 14 insertions(+), 12 deletions(-)
> >
> > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > index ceeeec9b7290..51751337f394 100644
> > --- a/net/ipv4/inet_hashtables.c
> > +++ b/net/ipv4/inet_hashtables.c
> > @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
> >         sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
> >                 score = compute_score(sk, net, hnum, daddr, dif, sdif);
> >                 if (score > hiscore) {
> > -                       result = inet_lookup_reuseport(net, sk, skb, doff,
> > -                                                      saddr, sport, daddr, hnum, inet_ehashfn);
> > -                       if (result)
> > -                               return result;
> > -
> >                         result = sk;
> >                         hiscore = score;
> >                 }
> >         }
> >
> > -       return result;
> > +       if (!result)
> > +               return NULL;
> > +
> > +       sk = inet_lookup_reuseport(net, result, skb, doff,
> > +                                  saddr, sport, daddr, hnum, inet_ehashfn);
> > +
> > +       return sk ? sk : result;
> >  }
>
> IMHO, I don't see it as a bugfix. So can you elaborate on what the exact
> side effect you're faced with is when the algorithm finally prefers
> socket2 (without
> this patch)?

Hi, Jason. The case is that the user has several NIC,
and there are some sockets that are binded to them,
who listen on TCP port 6666. And a global socket doesn't
bind any NIC and listens on TCP port 6666.

In theory, the connection request from the NIC will goto
the listen socket that is binded on it. When on socket
is binded on the NIC, it goto the global socket. However,
the connection request always goto the global socket, which
is not expected.

What's worse is that when TCP MD5 is used on the socket,
the connection will fail :/

More discussion can be found here:
https://lore.kernel.org/netdev/20250801090949.129941-1-dongml2@chinatelecom.cn/
https://lore.kernel.org/netdev/20250731123309.184496-1-dongml2@chinatelecom.cn/

>
> AFAIK, the current approach breaks the initial design and might make
> the whole lookup process take a longer time in certain cases like you mentioned.

Kuniyuki said he will post some patch when the net-next is
open, which reorder the socket in __inet_hash() to make
the reuseport socket lookup keep O(1).

So this patch is more like a temporary solution :/

Thanks!
Menglong Dong

>
> Thanks,
> Jason

On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> >
> > Hi Menglong,
> >
> > On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > >
> > > For now, the tcp socket lookup will terminate if the socket is reuse port
> > > in inet_lhash2_lookup(), which makes the socket is not the best match.
> > >
> > > For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> > > but socket1 bind on "eth0". We create socket1 first, and then socket2.
> > > Then, all connections will goto socket2, which is not expected, as socket1
> > > has higher priority.
> > >
> > > This can cause unexpected behavior if TCP MD5 keys is used, as described
> > > in Documentation/networking/vrf.rst -> Applications.
> > >
> > > Therefor, we lookup the best matched socket first, and then do the reuse
> >
> > s/Therefor/Therefore
> >
> > > port logic. This can increase some overhead if there are many reuse port
> > > socket :/
> > >
> > > Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
> > > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > > ---
> > > v3:
> > > * use the approach in V1
> > > * add the Fixes tag
> > > ---
> > >  net/ipv4/inet_hashtables.c  | 13 +++++++------
> > >  net/ipv6/inet6_hashtables.c | 13 +++++++------
> > >  2 files changed, 14 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > > index ceeeec9b7290..51751337f394 100644
> > > --- a/net/ipv4/inet_hashtables.c
> > > +++ b/net/ipv4/inet_hashtables.c
> > > @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
> > >         sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
> > >                 score = compute_score(sk, net, hnum, daddr, dif, sdif);
> > >                 if (score > hiscore) {
> > > -                       result = inet_lookup_reuseport(net, sk, skb, doff,
> > > -                                                      saddr, sport, daddr, hnum, inet_ehashfn);
> > > -                       if (result)
> > > -                               return result;
> > > -
> > >                         result = sk;
> > >                         hiscore = score;
> > >                 }
> > >         }
> > >
> > > -       return result;
> > > +       if (!result)
> > > +               return NULL;
> > > +
> > > +       sk = inet_lookup_reuseport(net, result, skb, doff,
> > > +                                  saddr, sport, daddr, hnum, inet_ehashfn);
> > > +
> > > +       return sk ? sk : result;
> > >  }
> >
> > IMHO, I don't see it as a bugfix. So can you elaborate on what the exact
> > side effect you're faced with is when the algorithm finally prefers
> > socket2 (without
> > this patch)?
>
> Hi, Jason. The case is that the user has several NIC,
> and there are some sockets that are binded to them,
> who listen on TCP port 6666. And a global socket doesn't
> bind any NIC and listens on TCP port 6666.
>
> In theory, the connection request from the NIC will goto
> the listen socket that is binded on it. When on socket
> is binded on the NIC, it goto the global socket. However,
> the connection request always goto the global socket, which
> is not expected.
>
> What's worse is that when TCP MD5 is used on the socket,
> the connection will fail :/

I'm trying to picture what the usage can be in the userland as you
pointed out in the MD5 case. As to the client side, it seems weird
since it cannot detect and know the priority of the other side where a
few sockets listen on the same address and port.

I'm not saying the priority problem doesn't exist, just not knowing
how severe the case could be. It doesn't look that bad at least until
now. Only the selection policy itself matters more to the server side
than to the client side.

Thanks,
Jason

On Sun, Aug 3, 2025 at 10:54 AM Jason Xing <kerneljasonxing@gmail.com> wrote:
>
> On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> >
> > On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > >
> > > Hi Menglong,
> > >
> > > On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > > >
> > > > For now, the tcp socket lookup will terminate if the socket is reuse port
> > > > in inet_lhash2_lookup(), which makes the socket is not the best match.
> > > >
> > > > For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> > > > but socket1 bind on "eth0". We create socket1 first, and then socket2.
> > > > Then, all connections will goto socket2, which is not expected, as socket1
> > > > has higher priority.
> > > >
> > > > This can cause unexpected behavior if TCP MD5 keys is used, as described
> > > > in Documentation/networking/vrf.rst -> Applications.
> > > >
> > > > Therefor, we lookup the best matched socket first, and then do the reuse
> > >
> > > s/Therefor/Therefore
> > >
> > > > port logic. This can increase some overhead if there are many reuse port
> > > > socket :/
> > > >
> > > > Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
> > > > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > > > ---
> > > > v3:
> > > > * use the approach in V1
> > > > * add the Fixes tag
> > > > ---
> > > >  net/ipv4/inet_hashtables.c  | 13 +++++++------
> > > >  net/ipv6/inet6_hashtables.c | 13 +++++++------
> > > >  2 files changed, 14 insertions(+), 12 deletions(-)
> > > >
> > > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > > > index ceeeec9b7290..51751337f394 100644
> > > > --- a/net/ipv4/inet_hashtables.c
> > > > +++ b/net/ipv4/inet_hashtables.c
> > > > @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
> > > >         sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
> > > >                 score = compute_score(sk, net, hnum, daddr, dif, sdif);
> > > >                 if (score > hiscore) {
> > > > -                       result = inet_lookup_reuseport(net, sk, skb, doff,
> > > > -                                                      saddr, sport, daddr, hnum, inet_ehashfn);
> > > > -                       if (result)
> > > > -                               return result;
> > > > -
> > > >                         result = sk;
> > > >                         hiscore = score;
> > > >                 }
> > > >         }
> > > >
> > > > -       return result;
> > > > +       if (!result)
> > > > +               return NULL;
> > > > +
> > > > +       sk = inet_lookup_reuseport(net, result, skb, doff,
> > > > +                                  saddr, sport, daddr, hnum, inet_ehashfn);
> > > > +
> > > > +       return sk ? sk : result;
> > > >  }
> > >
> > > IMHO, I don't see it as a bugfix. So can you elaborate on what the exact
> > > side effect you're faced with is when the algorithm finally prefers
> > > socket2 (without
> > > this patch)?
> >
> > Hi, Jason. The case is that the user has several NIC,
> > and there are some sockets that are binded to them,
> > who listen on TCP port 6666. And a global socket doesn't
> > bind any NIC and listens on TCP port 6666.
> >
> > In theory, the connection request from the NIC will goto
> > the listen socket that is binded on it. When on socket
> > is binded on the NIC, it goto the global socket. However,
> > the connection request always goto the global socket, which
> > is not expected.
> >
> > What's worse is that when TCP MD5 is used on the socket,
> > the connection will fail :/
>
> I'm trying to picture what the usage can be in the userland as you
> pointed out in the MD5 case. As to the client side, it seems weird
> since it cannot detect and know the priority of the other side where a
> few sockets listen on the same address and port.

For the server side, it needs to add all the clients information
with the TCP_MD5SIG option. For socket1 that binded on the
eth0, it will add all the client addresses that come from eth0 to the
socket1 with TCP_MD5SIG. So the server knows the clients.

And in my use case, the TCP MD5 + VRF is used. The details are
a little fuzzy for me, which I need to do some recalling :/

>
> I'm not saying the priority problem doesn't exist, just not knowing
> how severe the case could be. It doesn't look that bad at least until
> now. Only the selection policy itself matters more to the server side
> than to the client side.
>
> Thanks,
> Jason

On Sun, Aug 3, 2025 at 12:00 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> On Sun, Aug 3, 2025 at 10:54 AM Jason Xing <kerneljasonxing@gmail.com> wrote:
> >
> > On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > >
> > > On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > > >
> > > > Hi Menglong,
> > > >
> > > > On Sat, Aug 2, 2025 at 5:28 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > > > >
> > > > > For now, the tcp socket lookup will terminate if the socket is reuse port
> > > > > in inet_lhash2_lookup(), which makes the socket is not the best match.
> > > > >
> > > > > For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> > > > > but socket1 bind on "eth0". We create socket1 first, and then socket2.
> > > > > Then, all connections will goto socket2, which is not expected, as socket1
> > > > > has higher priority.
> > > > >
> > > > > This can cause unexpected behavior if TCP MD5 keys is used, as described
> > > > > in Documentation/networking/vrf.rst -> Applications.
> > > > >
> > > > > Therefor, we lookup the best matched socket first, and then do the reuse
> > > >
> > > > s/Therefor/Therefore
> > > >
> > > > > port logic. This can increase some overhead if there are many reuse port
> > > > > socket :/
> > > > >
> > > > > Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection")
> > > > > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > > > > ---
> > > > > v3:
> > > > > * use the approach in V1
> > > > > * add the Fixes tag
> > > > > ---
> > > > >  net/ipv4/inet_hashtables.c  | 13 +++++++------
> > > > >  net/ipv6/inet6_hashtables.c | 13 +++++++------
> > > > >  2 files changed, 14 insertions(+), 12 deletions(-)
> > > > >
> > > > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > > > > index ceeeec9b7290..51751337f394 100644
> > > > > --- a/net/ipv4/inet_hashtables.c
> > > > > +++ b/net/ipv4/inet_hashtables.c
> > > > > @@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
> > > > >         sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
> > > > >                 score = compute_score(sk, net, hnum, daddr, dif, sdif);
> > > > >                 if (score > hiscore) {
> > > > > -                       result = inet_lookup_reuseport(net, sk, skb, doff,
> > > > > -                                                      saddr, sport, daddr, hnum, inet_ehashfn);
> > > > > -                       if (result)
> > > > > -                               return result;
> > > > > -
> > > > >                         result = sk;
> > > > >                         hiscore = score;
> > > > >                 }
> > > > >         }
> > > > >
> > > > > -       return result;
> > > > > +       if (!result)
> > > > > +               return NULL;
> > > > > +
> > > > > +       sk = inet_lookup_reuseport(net, result, skb, doff,
> > > > > +                                  saddr, sport, daddr, hnum, inet_ehashfn);
> > > > > +
> > > > > +       return sk ? sk : result;
> > > > >  }
> > > >
> > > > IMHO, I don't see it as a bugfix. So can you elaborate on what the exact
> > > > side effect you're faced with is when the algorithm finally prefers
> > > > socket2 (without
> > > > this patch)?
> > >
> > > Hi, Jason. The case is that the user has several NIC,
> > > and there are some sockets that are binded to them,
> > > who listen on TCP port 6666. And a global socket doesn't
> > > bind any NIC and listens on TCP port 6666.
> > >
> > > In theory, the connection request from the NIC will goto
> > > the listen socket that is binded on it. When on socket
> > > is binded on the NIC, it goto the global socket. However,
> > > the connection request always goto the global socket, which
> > > is not expected.
> > >
> > > What's worse is that when TCP MD5 is used on the socket,
> > > the connection will fail :/
> >
> > I'm trying to picture what the usage can be in the userland as you
> > pointed out in the MD5 case. As to the client side, it seems weird
> > since it cannot detect and know the priority of the other side where a
> > few sockets listen on the same address and port.
>
> For the server side, it needs to add all the clients information
> with the TCP_MD5SIG option. For socket1 that binded on the
> eth0, it will add all the client addresses that come from eth0 to the
> socket1 with TCP_MD5SIG. So the server knows the clients.

Right, but I meant the _client_ side doesn't know the details of the
other side, that is to say, the server side needs to keep sure the
client server easily connects to your preferred listener regardless of
what the selection algorithm looks like. In terms of what you
depicted, I see your point. One question is if the kernel or API
provides any rules and instructions to the users that on the server
side the sk1 must be selected in your case? Is it possible for other
cases where the sk2 is the preferable/ideal one? I'm not sure if it's
worth 'fixing' it in the kernel.

Thanks,
Jason

On Sun, Aug 3, 2025 at 4:32 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
>
> On Sun, Aug 3, 2025 at 12:00 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> >
> > On Sun, Aug 3, 2025 at 10:54 AM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > >
> > > On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > > >
> > > > On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > > > >
[......]
> > >
> > > I'm trying to picture what the usage can be in the userland as you
> > > pointed out in the MD5 case. As to the client side, it seems weird
> > > since it cannot detect and know the priority of the other side where a
> > > few sockets listen on the same address and port.
> >
> > For the server side, it needs to add all the clients information
> > with the TCP_MD5SIG option. For socket1 that binded on the
> > eth0, it will add all the client addresses that come from eth0 to the
> > socket1 with TCP_MD5SIG. So the server knows the clients.
>
> Right, but I meant the _client_ side doesn't know the details of the
> other side, that is to say, the server side needs to keep sure the
> client server easily connects to your preferred listener regardless of
> what the selection algorithm looks like. In terms of what you
> depicted, I see your point. One question is if the kernel or API
> provides any rules and instructions to the users that on the server
> side the sk1 must be selected in your case? Is it possible for other
> cases where the sk2 is the preferable/ideal one? I'm not sure if it's
> worth 'fixing' it in the kernel.

What does sk2 represent here? I don't think that the sk2 should
be preferable. For now, it is selected by the creating order, and
there should not be a case that relies on the socket creation
order......would it?

So the socket should be selected by priority, and sk1, which is binded
on eth0, has higher priority, which is awarded by the users.

I noticed that the net-next is open, so we can use Kuniyuki's
solution instead, which is better for the performance ;)

Thanks!
Menglong Dong

On Wed, Aug 13, 2025 at 5:55 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> On Sun, Aug 3, 2025 at 4:32 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> >
> > On Sun, Aug 3, 2025 at 12:00 PM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > >
> > > On Sun, Aug 3, 2025 at 10:54 AM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > > >
> > > > On Sun, Aug 3, 2025 at 9:59 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
> > > > >
> > > > > On Sat, Aug 2, 2025 at 9:06 PM Jason Xing <kerneljasonxing@gmail.com> wrote:
> > > > > >
> [......]
> > > >
> > > > I'm trying to picture what the usage can be in the userland as you
> > > > pointed out in the MD5 case. As to the client side, it seems weird
> > > > since it cannot detect and know the priority of the other side where a
> > > > few sockets listen on the same address and port.
> > >
> > > For the server side, it needs to add all the clients information
> > > with the TCP_MD5SIG option. For socket1 that binded on the
> > > eth0, it will add all the client addresses that come from eth0 to the
> > > socket1 with TCP_MD5SIG. So the server knows the clients.
> >
> > Right, but I meant the _client_ side doesn't know the details of the
> > other side, that is to say, the server side needs to keep sure the
> > client server easily connects to your preferred listener regardless of
> > what the selection algorithm looks like. In terms of what you
> > depicted, I see your point. One question is if the kernel or API
> > provides any rules and instructions to the users that on the server
> > side the sk1 must be selected in your case? Is it possible for other
> > cases where the sk2 is the preferable/ideal one? I'm not sure if it's
> > worth 'fixing' it in the kernel.
>
> What does sk2 represent here? I don't think that the sk2 should
> be preferable. For now, it is selected by the creating order, and
> there should not be a case that relies on the socket creation
> order......would it?
>
> So the socket should be selected by priority, and sk1, which is binded
> on eth0, has higher priority, which is awarded by the users.
>
> I noticed that the net-next is open, so we can use Kuniyuki's
> solution instead, which is better for the performance ;)

I'll post a series next week when Eric is back.