Back in the days when RTM_NEWLINK wasn't yet implemented, people had to
rely upon kernel modules to create (virtual) interfaces for them. The
number of those was usually defined via module parameter, and a sane
default value was chosen. Now that iproute2 allows users to instantiate
new interfaces at will, this is no longer required - though for
backwards compatibility reasons, we're stuck with both methods which
collide at the point when one tries to create an interface with a
standard name for a type which exists in a kernel module: The kernel
will load the module, which instantiates the interface and the following
RTM_NEWLINK request will fail since the interface exists already. For
instance:
| # lsmod | grep dummy
| # ip link show | grep dummy0
| # ip link add dummy0 type dummy
| RTNETLINK answers: File exists
| # ip link show | grep -c dummy0
| 1
There is no race-free solution in userspace for this dilemma as far as I
can tell, so try to detect whether a user might have run into this and
notify that the given error message might be irrelevant.
Signed-off-by: Phil Sutter <p...@nwl.cc>
---
ip/iplink.c | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/ip/iplink.c b/ip/iplink.c
index 5aff2fde38dae..f94fa96668d21 100644
--- a/ip/iplink.c
+++ b/ip/iplink.c
@@ -867,6 +867,33 @@ int iplink_parse(int argc, char **argv, struct iplink_req
*req,
return ret - argc;
}
+static bool link_name_is_standard(const char *type, const char *name)
+{
+ const struct {
+ const char *type;
+ const char *name;
+ } standard_links[] = {
+ { "dummy", "dummy0" },
+ { "ifb", "ifb0" },
+ { "ifb", "ifb1" },
+ { "bond", "bond0" },
+ { "ipip", "tunl0" },
+ { "gre", "gre0" },
+ { "gretap", "gretap0" },
+ { "vti", "ip_vti0" },
+ { "sit", "sit0" },
+ };
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(standard_links); i++) {
+ if (strcmp(type, standard_links[i].type) ||
+ strcmp(name, standard_links[i].name))
+ continue;
+ return true;
+ }
+ return false;
+}
+
static int iplink_modify(int cmd, unsigned int flags, int argc, char **argv)
{
int len;
@@ -1007,8 +1034,14 @@ static int iplink_modify(int cmd, unsigned int flags,
int argc, char **argv)
return -1;
}
- if (rtnl_talk(&rth, &req.n, NULL, 0) < 0)
+ if (rtnl_talk(&rth, &req.n, NULL, 0) < 0) {
+ if (errno == EEXIST &&
+ flags & NLM_F_CREATE &&
+ link_name_is_standard(type, name))
+ fprintf(stderr,
+ "Note: Kernel might have created interface upon
module load.\n");
return -2;
+ }
return 0;
}
--
2.13.1
