[augeas-devel] strange results using rm with the dhcpd lense

[Robert Drake]

On 3/16/2014 5:35 AM, Raphaël Pinson wrote:
> Upon thinking about it some more, this is only problematic when 
> removing or inserting before existing blocks.
>
> That said, it would be great to write lenses that avoid this kind of 
> situation. The obvious way to do that would be to use seq on blocks 
> (using them on subnets wouldn't solve the problem for hosts, etc.), so 
> you'd have:
>
>     "subnet 10.152.187.0 netmask 255.255.255.0 {}\n"
>
> mapped as
>
>     { "1" = "subnet"
>       { "network" = "10.152.187.0" }
>       { "netmask" = "255.255.255.0" }
>     }
>
> etc.
>
> in order to retain formatting in each block.
>
>
> Obviously, this is an incompatible change, which would have to be made 
> in every lens that was written this way, so we need to ponder whether 
> it is an acceptable change.
>

Yeah.  In the case of DHCPD it seems that the entire lense was written 
without consideration for deleting data (or at least without the 
consideration of deleting statement blocks).  I would argue that this is 
a bug because it breaks peoples expectations for lenses. The docs say 
that existing formatting will be preserved, but if you delete things 
above a block then the formatting gets shifted and lost.   It seems 
weird that the formatting information isn't saved with the data tree.. 
normally you would expect that formatting for the block that is being 
deleted gets taken with it.

The question would be if there are scripts out there that depend on the 
way things work now that would break if it were changed though.

It looks like the only real fix from within the lense is to do as you 
say and rewrite it so shared-networks, pools, subnets and groups are all 
sequences.  That breaks everyones existing scripts though.

I'm somewhat surprised this hasn't come up before, but I think I'm using 
augeas differently than most people.  Most of the time people probably 
want to insert new statements or remove single statements. My goal is to 
programmatically manage a large DHCP file with hundreds of subnets.

Maybe a compromise would be not to break the existing way, but add a new 
command that let you mark a part of the tree as unused, then skip over 
that part when a "save" is called.



>
> Raphaël
>

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