Re: [PATCH v5 02/15] util: Extend sock_probe_mem() to sock_probe_features()

On Tue, 2 Dec 2025 15:02:02 +1100 David Gibson wrote:

sock_probe_mem() currently checks whether we're able to allocate large socket buffers. Extend it to also check whether the SO_BINDTODEVICE socket option is available. Rename to sock_probe_features() to reflect the new functionality.

Signed-off-by: David Gibson --- passt.c | 2 +- passt.h | 2 ++ util.c | 19 +++++++++++++++++-- util.h | 2 +- 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/passt.c b/passt.c index 4964427d..0b84ac6c 100644 --- a/passt.c +++ b/passt.c @@ -381,7 +381,7 @@ int main(int argc, char **argv) if (setrlimit(RLIMIT_NOFILE, &limit)) die_perror("Failed to set current limit for open files");

- sock_probe_mem(&c); + sock_probe_features(&c);

conf(&c, argc, argv); trace_init(c.trace); diff --git a/passt.h b/passt.h index 15801b44..79d01ddb 100644 --- a/passt.h +++ b/passt.h @@ -204,6 +204,7 @@ struct ip6_ctx { * @freebind: Allow binding of non-local addresses for forwarding * @low_wmem: Low probed net.core.wmem_max * @low_rmem: Low probed net.core.rmem_max + * @no_bindtodevice: Unprivileged SO_BINDTODEVICE not available * @vdev: vhost-user device * @device_state_fd: Device state migration channel * @device_state_result: Device state migration result @@ -281,6 +282,7 @@ struct ctx {

int low_wmem; int low_rmem; + int no_bindtodevice;

struct vu_dev *vdev;

diff --git a/util.c b/util.c index 347f34f5..bad38129 100644 --- a/util.c +++ b/util.c @@ -233,12 +233,13 @@ int sock_unix(char *sock_path) }

/** - * sock_probe_mem() - Check if setting high SO_SNDBUF and SO_RCVBUF is allowed + * sock_probe_features() - Probe for socket features we might use * @c: Execution context */ -void sock_probe_mem(struct ctx *c) +void sock_probe_features(struct ctx *c) { int v = INT_MAX / 2, s; + const char lo[] = "lo"; socklen_t sl;

s = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, IPPROTO_TCP); @@ -247,6 +248,7 @@ void sock_probe_mem(struct ctx *c) return; }

+ /* Check if setting high SO_SNDBUF and SO_RCVBUF is allowed */ sl = sizeof(v); if (setsockopt(s, SOL_SOCKET, SO_SNDBUF, &v, sizeof(v)) || getsockopt(s, SOL_SOCKET, SO_SNDBUF, &v, &sl) || @@ -259,6 +261,19 @@ void sock_probe_mem(struct ctx *c) (size_t)v < RCVBUF_BIG) c->low_rmem = 1;

+ /* Check if SO_BINDTODEVICE is available + * + * Supported since kernel version 5.7, commit c427bfec18f2 ("net: core: + * enable SO_BINDTODEVICE for non-root users"). Some distro kernels may + * have backports, of course. Record whether we can use it so that we + * can give more useful diagnostics. + */ + if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE, lo, sizeof(lo)-1)) {

Nit: our coding style uses spaces around arithmetic operators... I took the liberty of fixing this up on merge, though. -- Stefano