[augeas-devel] Re: using defnode to add new nodes

[Kjetil Torgrim Homme]

David Lutterkort <lutter at redhat.com> writes:

> On Wed, 2009-06-17 at 11:54 +0200, Kjetil Torgrim Homme wrote:
>> right.  I'm not suggesting that the variable defined by defnode is
>> changed *after* defnode returns.  I'm just suggesting that the node
>> defnode creates is included in the node list returned.
>
> Aaah .. all kinds of lights are going off .. you are saying that
> after doing a 'set' inside defnode, just stick the new node into the
> variable ? Yeah, I like that .. happen to have a patch ? ;)

oh, that's great!  unfortunately, I haven't quite understood the code
well enough yet.  I might have another go later.

>> I'm sure it's possible to come up with problematic examples, and I
>> encourage you to do so, so that we can discuss how Augeas is to be
>> *used*.  a little (but not much) more tricky example: defnode
>> doesn't work with the hosts lens, since it creates hosts/N/ rather
>> than hosts[N].
>
> Just as an aside: the reason the hosts lens creates a
> /files/etc/hosts/N node rather than something like
> /files/etc/hosts/entry[N] (i.e. uses the 'seq' lens) has to do how
> spacing is preserved. Basically, with the current scheme, Augeas can
> detect that an entry has been deleted, and make sure comments
> etc. stay in the right place. With the alternate scheme, deleting a
> host entry in the middle would cause all lines after the deleted
> line to shift up one line, past comments.

that doesn't seem to happen to me, but it looks like whitespace is
reset to lens defaults when I remove a node in the middle of, e.g.,
services.  here's an excerpt from the diff produced when I removed the
junk entry I had added manually.

@@ -26,59 +26,58 @@
 echo           7/tcp
 echo           7/udp
 # comment in front of junk
-junk           8/udp
 # comment after junk
-discard                9/tcp           sink null
+discard                9/tcp sink null
 discard                9/udp           sink null
 systat         11/tcp          users
 systat         11/udp          users
 daytime                13/tcp
 daytime                13/udp
-qotd           17/tcp          quote
+qotd           17/tcp quote
 qotd           17/udp          quote
-msp            18/tcp                          # message send protocol
+msp            18/tcp# message send protocol
 msp            18/udp                          # message send protocol
-chargen                19/tcp          ttytst source
+chargen                19/tcp ttytst source
[...]

isn't it strange that lines with udp and tcp behave differently?  this
is 0.5.1, btw.

>>         augtool> defnode host '/files/etc/hosts/*/*[../ipaddr = "127.0.0.1"]'
>>         Failed
>> 
>> first of all, such inconsistencies across lenses should be fixed.
>> secondly, I think it's quite reasonable that in the non-matching case,
>> defnode would create a new object at the level of the first wildcard.
>> in either case I would like to be able to say
>> 
>>         set $host/ipaddr 127.0.0.1
>>         set $host/canonical localhost
>>         set $host/alias[1] localhost.localdomain
>
> The problem is that at the point where the node is created, I have
> no idea what an appropriate name for the new node would be (since I
> only have the wildcard, I don't even know what regexp the label is
> supposed to match)

well... "001"? :-) no, I see it's hard to do without possibly dubious
heuristics.

-- 
Kjetil T. Homme
Redpill Linpro AS - Changing the game