>>
>> OK, I tried like this:
>>
>> exec sudo "$mktuntap" -pvB 3 \
>>   sudo -u "$USER" -C 4 \
>>    "$crosvm" run \
>>     -p init=/sbin/init \
>>     -p "spectrumcmd=$(printf %s "$command" | base64 -w0)" \
>>     --tap-fd 3 \
>>     --seccomp-log-failures \
>>     --root "$rootfs" \
>>     --host_ip 10.0.0.1 \
>>     --netmask 255.0.0.0 \
>>     --mac c0:ff:ee:c0:ff:ee \
>>     -m 4096 \
>>     "$@" \
>>     "$kernel"
>>
>> I got "sudo: you are not permitted to use the -C option", which I
>> fixed by editing the sudoers file. Then it fails with:
>>
>> [ERROR:src/main.rs:1351] The architecture failed to build the vm:
>> error creating devices: failed to set up virtio networking: failed to
>> open tap device: failed to create tap interface: Operation not
>> permitted (os error 1)
>>
>> Strace shows:
>>
>> openat(AT_FDCWD, "/dev/net/tun", O_RDWR|O_NONBLOCK|O_CLOEXEC) = 31
>> ioctl(31, TUNSETIFF, 0x7ffee7ede238) = -1 EPERM (Operation not permitted)
>>
>> Maybe it's just because my crosvm is too old?
>
> This is because if you specify --host_ip, --netmask, or --mac, crosvm
> will try to create its own TAP device.  If you omit all those arguments
> I think it should work.

Oh, whoops, I missed your reply about having worked this out already!