[augeas-devel] load specific lens

[David Lutterkort]

On Wed, 2010-03-10 at 16:25 +0100, Frederik Wagner wrote:
> On Wed, Mar 10, 2010 at 9:46 AM, Frederik Wagner <fnerdwq at googlemail.com> wrote:
> > 2. Would there be a way to inlcude the 'string' array handling into
> > the shellvars lens? Probably only by handling specific entries of
> > specific files (how do I test for the scanned file in a lens?)
> > diferently, I suppose?
> 
> As a (working) test I included the functionality into the shellvars
> lens to treat specific keywords as an array of words.
> This works fine (even if one has to keep an explicit list of keywords
> which have to be treated in this way), but for the fact that the lens
> is _incredibly_ slow now and using a _lot_ of memory.

Where are you seeing the slowdown ? With augtool or augparse ?
Generally, these kinds of lenses cause the typechecker to work very hard
- the typechecker is only run by augparse. You can bypass it with
'augparse --notypecheck'; though before declaring any changes 'done',
you need to typecheck the lens at least once.

> To filter or the keywords I'm using - just showing the relevant adjustments:
> 
> ...
>   (* keywords from files which should be treaded as array of words *)
>   let key_wa =
>                (* from /etc/sysconfig/kernel *)
>                "MODULES_LOADED_ON_BOOT"
>              | "DOMU_INITRD_MODULES"
>              | "INITRD_MODULES"
>                (* from /etc/sysconfig/bootloader *)
>              | "DEFAULT_APPEND"
>              | "FAILSAFE_APPEND"
>              | "XEN_KERNEL_APPEND"
>              | "XEN_APPEND"
>              | "RT_APPEND"
> 
>   let key_re = /[A-Za-z0-9_]+(\[[0-9]+\])?/ - "unset" - "export" - key_wa
> ...
> 
> and later in the lens I'm applying extras steps to the filtered keywords:
> 
> ...
>   let char_wa = /[^ "\t\n]/
> 
>   (* for the keywords in key_wa treat the values as an array of words *)
>   let wa_array = let char_wa = /[^ "\t\n]/
>     let wa_array_value = store char_wa+ in
>     del /\"[ \t]*/ "\"" . counter "wa_val" .
>       [ seq "wa_val" .wa_array_value ] .
>       [ del /[ \t\n]+/ " "  . seq "wa_val" . wa_array_value ] *
>       . del /[ \t]*\"/ "\""
> 
>   (* lens for the array of words, extra handling of empty strings "" *)
>   let wa_kv = [ key key_wa . eq . (del "\"\"" "\"\""|wa_array) . eol ]
> 
>   let lns = ( comment | empty | source | kv | unset | wa_kv ) *
> ...
> 
> Since I change the fast working original shellvars lens, I suppose the
> filtering construct is the problem.
> 
> Am I doing something wrong? Or is the adjustment of the shellvars lens
> generally not usefull anyway? (if it is I would submit the patch, when
> I'm ready).

Another way to structure this is to make the current lens 'lns' a
function that takes the special variables as an argument, so that you'd
have

  let wa (keys:regexp) =
    ( comment | empty | source | kv | unset | wa_kv keys) *

and change wa_kv to pass keys respectively (key_re - key_wa) to the
right parts of the lens.

Then, write separate transforms and filters for each file, e.g.

  let kernel_xfm =
    let wa_keys = /MODULES_LOADED_ON_BOOT|DOMU_INITRD_MODULES|INITRD_MODULES/ in
    transform (wa wa_keys) (incl "/etc/sysconfig/kernel")

There's one minor hitch though: Augeas right now only allows one
autoload statement per module. That will force you to have separate
modules for each file that you want to handle that way, e.g.

        module Shellvars_kernel =
          autoload xfm
        
          let lns = Shellvars.wa /MODULES_LOADED_ON_BOOT|DOMU_INITRD_MODULES|INITRD_MODULES/
          let xfm = transform lns (incl "/etc/sysconfig/kernel")
        
David