My first approach to this was to condition the use of SO_PEEK_OFF with
tcpv4, e.g., basically
a test like if (v4 && peek_offset_cap) {...} everywhere, but then I made
an interesting discovery.
It turns out that, unless the ´-4' option is explicitly given on the
command line, all sockets are
v6, even those that are later used as v4 sockets. So, the set_peek_off()
call failed even
for supposedly v4 sockets.
I checked this by adding a printout to the tcp_listen_handler(), and
noticed that all returns from
the accept4() call goes into the AF_INET6 branch, even when the client
(iperf3) call is using an IPv4 address.
During traffic, the very same socket is marked as v4 in the tcp_tap_conn
structure, and this seems to
have worked just fine until I added the set_peek_offset call().
I believe this is an issue that has been introduced during the last
months, since I didn't start
using the ´-4' option consistently until some months ago, and then it
worked.
Happy summer
///jon
On 2024-07-20 09:54, Jon Maloy wrote:
The recently added socket option SO_PEEK_OFF is not
supported for
TCP/IPv6 sockets. Until we get that support into the kernel we need to
test for support in both protocols to set the global 'peek_offset_cap´
to true.
Signed-off-by: Jon Maloy <jmaloy(a)redhat.com>
---
tcp.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)
diff --git a/tcp.c b/tcp.c
index c5431f1..32026ca 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2717,6 +2717,28 @@ static void tcp_sock_refill_init(const struct ctx *c)
}
}
+/**
+ * tcp_probe_peek_offset_cap() - Check if SO_PEEK_OFF is supported by kernel
+ * @af: Address family, IPv4 or IPv6
+ *
+ * Return: true if supported, false otherwise
+ */
+bool tcp_probe_peek_offset_cap(int af)
+{
+ bool ret = false;
+ int s, optv = 0;
+
+ s = socket(af, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP);
+ if (s < 0) {
+ warn_perror("Temporary TCP socket creation failed");
+ } else {
+ if (!setsockopt(s, SOL_SOCKET, SO_PEEK_OFF, &optv, sizeof(int)))
+ ret = true;
+ close(s);
+ }
+ return ret;
+}
+
/**
* tcp_init() - Get initial sequence, hash secret, initialise per-socket data
* @c: Execution context
@@ -2725,8 +2747,7 @@ static void tcp_sock_refill_init(const struct ctx *c)
*/
int tcp_init(struct ctx *c)
{
- unsigned int b, optv = 0;
- int s;
+ unsigned int b;
ASSERT(!c->no_tcp);
@@ -2752,15 +2773,8 @@ int tcp_init(struct ctx *c)
NS_CALL(tcp_ns_socks_init, c);
}
- /* Probe for SO_PEEK_OFF support */
- s = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP);
- if (s < 0) {
- warn_perror("Temporary TCP socket creation failed");
- } else {
- if (!setsockopt(s, SOL_SOCKET, SO_PEEK_OFF, &optv, sizeof(int)))
- peek_offset_cap = true;
- close(s);
- }
+ peek_offset_cap = tcp_probe_peek_offset_cap(AF_INET) &&
+ tcp_probe_peek_offset_cap(AF_INET6);
info("SO_PEEK_OFF%ssupported", peek_offset_cap ? " " : " not
");
return 0;