Old habits :) Fixed.

having duplicate names is going to cause trouble in multiple areas

Do you have any examples? I don't believe this is true.
There's nothing intrinsic to the system that means that VNIC names need to be globally unique, they just need to be unique within a zone. SmartOS uses duplicate VNICs widely (each zone has a net0 interface for example) and I have a branch in OmniOS where I'm experimenting with that for a possible future update; it's working well.
The specific bug that I'm fixing here is that if moving a VNIC to a zone results in a name collision, then dlmgmtd crashes and will not restart, resulting in a system where links cannot be managed.



Also, leaving the zone in a down state doesn't really help - there's no indication as to what the problem is, how to fix it, or even if it's possible to fix it.

Well, there's this:

bloody# zoneadm -z test halt
zone 'test': datalinks remain in zone after shutdown
zone 'test': unable to unconfigure network interfaces in zone
zone 'test': unable to destroy zone


more could be printed (or syslogged) in the case that the link move returns EEXIST I suppose.

Persistent datalinks have to be unique within a zone. But that's exactly
the situation here.

Imagine the following scenarios

create vnic with name vnic0
create zone using vnic0
create new vnic with name vnic0
delete vnic0
reboot

and the zone won't come up because the vnic has actually gone

create vnic with name vnic0
create zone using vnic0
create new vnic with name vnic0 over different interface
reboot

and the zone will boot attached to the new interface rather than the
old one

The point is that datalink.conf (which is where persistent
configuration is stored) assumes that the link name is unique. If you
create a duplicate, it deletes the old entry and replaces it with the
new one; if you delete it, then there will be no persistent entry.


The dlmgmtd service can be cleared, but may well come up in a different
configuration due to the above.

Links can be created with -t to stop them being written to the persistent store, which is what SmartOS and my branch do, but you have convinced me. I've added a patch that prevents the creation of any link with a duplicate name.

bloody% dladm show-vnic
bloody% pfzsh
bloody# dladm create-vnic -l vioif0 test0
bloody# dladm show-vnic
LINK         OVER       SPEED MACADDRESS        MACADDRTYPE VID  ZONE
test0        vioif0     1000  2:8:20:7d:48:2    random      0    --
bloody# dladm create-vnic -l vioif0 test0
dladm: vnic creation over vioif0 failed: object already exists
bloody# zoneadm -z test boot
bloody# dladm show-vnic
LINK         OVER       SPEED MACADDRESS        MACADDRTYPE VID  ZONE
test0        vioif0     1000  2:8:20:7d:48:2    random      0    test
bloody# dladm create-vnic -l vioif0 test0
dladm: vnic creation over vioif0 failed: object already exists