* [iproute PATCH] iplink: Notify user if EEXIST error might be spurious
@ 2017-08-01 17:27 Phil Sutter
2017-08-03 22:52 ` Stephen Hemminger
0 siblings, 1 reply; 2+ messages in thread
From: Phil Sutter @ 2017-08-01 17:27 UTC (permalink / raw)
To: Stephen Hemminger; +Cc: netdev
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 <phil@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
^ permalink raw reply related [flat|nested] 2+ messages in thread* Re: [iproute PATCH] iplink: Notify user if EEXIST error might be spurious
2017-08-01 17:27 [iproute PATCH] iplink: Notify user if EEXIST error might be spurious Phil Sutter
@ 2017-08-03 22:52 ` Stephen Hemminger
0 siblings, 0 replies; 2+ messages in thread
From: Stephen Hemminger @ 2017-08-03 22:52 UTC (permalink / raw)
To: Phil Sutter; +Cc: netdev
On Tue, 1 Aug 2017 19:27:47 +0200
Phil Sutter <phil@nwl•cc> wrote:
> 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 <phil@nwl•cc>
There is already a workable solution. There is already module parameters to block autocreation
in bonding and dummy network device. The others should have it as well.
This patch just seems like creating more clutter.
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