[arch-projects] [netctl] Still some weird behaviour with bridges

[Jouke Witteveen]

On Mon, May 6, 2013 at 7:36 PM, Dave Reisner <d at falconindy.com> wrote:
> On Mon, May 06, 2013 at 07:23:58PM +0200, Jouke Witteveen wrote:
>> On Mon, May 6, 2013 at 10:22 AM, Thomas Bächler <thomas at archlinux.org> wrote:
>> > I have this profile:
>> >
>> > Interface=vmnet
>> > Connection=bridge
>> > BindsToInterfaces=()
>> > IP=static
>> > SkipNoCarrier=yes
>> > Address=('1.2.3.4/5')
>> >
>> > While it seems to work fine, systemd prints these messages:
>> >
>> > Starting network profile 'vmnet'...
>> > Cannot find device "on"
>> > Usage: ip addr {add|change|replace} IFADDR dev STRING [ LIFETIME ]
>> > [ CONFFLAG-LIST ]
>> > ip addr del IFADDR dev STRING
>> > ip addr {show|save|flush} [ dev STRING ] [ scope SCOPE-ID ]
>> > [ to PREFIX ] [ FLAG-LIST ] [ label PATTERN ] [up]
>> > ip addr {showdump|restore}
>> > IFADDR := PREFIX | ADDR peer PREFIX
>> > [ broadcast ADDR ] [ anycast ADDR ]
>> > [ label STRING ] [ scope SCOPE-ID ]
>> > SCOPE-ID := [ host | link | global | NUMBER ]
>> > FLAG-LIST := [ FLAG-LIST ] FLAG
>> > FLAG  := [ permanent | dynamic | secondary | primary |
>> > tentative | deprecated | dadfailed | temporary |
>> > CONFFLAG-LIST ]
>> > CONFFLAG-LIST := [ CONFFLAG-LIST ] CONFFLAG
>> > CONFFLAG  := [ home | nodad ]
>> > LIFETIME := [ valid_lft LFT ] [ preferred_lft LFT ]
>> > LFT := forever | SECONDS
>> > interface  does not exist!
>> > Started network profile 'vmnet'
>> >
>> > This is most likely related to netctl not handling the empty
>> > BindsToInterfaces properly.
>> >
>>
>> You are right. This (arrays in Bash) is pretty tricky. I believe it is
>> fixed now. If so, the fix will land in netctl 1.1.
>>
>> Thanks,
>> - Jouke
>
> The problem is that you're declaring it initially as a string, and then
> expecting it to be an array. You simply cannot interchange the types
> without encountering unwanted behavior like this.

I'd like to keep the possibility of having declarations like this in a profile:

  Address='1.2.3.4/5'

Although Address is treated like an array internally, this works. As
far as I can tell it is relatively safe to treat non-empty strings as
1-element arrays.

> Note that you're still doing this in src/netctl.in:112. I'll also point
> out that your -v check allows people to create profiles that do not bind
> to any interfaces since it checks for the definition and not the
> existence of a value -- are you sure you want this?

Regarding src/netctl.in:112, the variable is set to a non-empty string
(in src/lib/globals:load_profile, it is actually verified that
$Interface is non-empty). By the above safety assumption, this should
be acceptable.
The current behavior is to bind to the Interface by default. By
explicitly setting BindsToInterfaces, this behavior can be altered.
Indeed, it is possible to do

  BindsToInterfaces=''

in a profile, which will most likely screw things up (it will instruct
systemd to bind to a device without a name). However, I consider this
a usage error. The current configuration allows setting
BindsToInterfaces to a possibly empty array as well as specifying it
correctly by a non-empty string. Those are the uses that I would like
to support. If a better way exists, I'd be happy to hear about it :-).

Thanks,
- Jouke