[PATCH 1/3] conf: Introduce --no-bindtodevice option for testing

[David Gibson <david@gibson.dropbear.id.au>]

We need to support (as best we can) older kernels which don't allow
unprivilieged processes to use the SO_BINDTODEVICE socket option.
Fallcaks for that case are controlled by the c->no_bindtodevice variable.

Currently testing behaviour of those fallbacks requires setting up a test
system with a kernel that doesn't support the option, which is pretty
awkward.  We can test it almost as well and much more easily by adding a
command line option to explicitly disable use of SO_BINDTODEVICE.

Like --no-splice this is envisaged as something for developers' and
testers' convenience, not a supported option for end users.  The man page
text reflects that.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 conf.c  | 2 ++
 passt.1 | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/conf.c b/conf.c
index ceb9aa55..70ea168c 100644
--- a/conf.c
+++ b/conf.c
@@ -962,6 +962,7 @@ static void usage(const char *name, FILE *f, int status)
 		"  --no-ndp		Disable NDP responses\n"
 		"  --no-dhcpv6		Disable DHCPv6 server\n"
 		"  --no-ra		Disable router advertisements\n"
+		"  --no-bindtodevice	Disable SO_BINDTODEVICE\n"
 		"  --freebind		Bind to any address for forwarding\n"
 		"  --no-map-gw		Don't map gateway address to host\n"
 		"  -4, --ipv4-only	Enable IPv4 operation only\n"
@@ -1454,6 +1455,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"no-dhcpv6",	no_argument,		&c->no_dhcpv6,	1 },
 		{"no-ndp",	no_argument,		&c->no_ndp,	1 },
 		{"no-ra",	no_argument,		&c->no_ra,	1 },
+		{"no-bindtodevice", no_argument,	&c->no_bindtodevice, 1},
 		{"no-splice",	no_argument,		&c->no_splice,	1 },
 		{"freebind",	no_argument,		&c->freebind,	1 },
 		{"no-map-gw",	no_argument,		&no_map_gw,	1 },
diff --git a/passt.1 b/passt.1
index db0d6620..4859d9e5 100644
--- a/passt.1
+++ b/passt.1
@@ -348,6 +348,12 @@ namespace will be silently dropped.
 Disable Router Advertisements. Router Solicitations coming from guest or target
 namespace will be ignored.
 
+.TP
+.BR \-\-no-bindtodevice
+Development/testing option, do not use.  Disables use of
+SO_BINDTODEVICE socket option.  Implicitly enabled on older kernels
+which don't permit unprivileged use of SO_BINDTODEVICE.
+
 .TP
 .BR \-\-freebind
 Allow any binding address to be specified for \fB-t\fR and \fB-u\fR
-- 
2.52.0