[augeas-devel] Migrating config file formats

[Doug Warner]

Sorry for the long delay here; starting to come back around to this problem :)

I really like your idea for supporting multiple syntaxes here and marking them
with this type of "version" string (you could label each syntax for each
matching version to make it easier to understand what is going on).

So, related to this; would it be possible to include an external lens to
handle the parsing for the "old version" and write the new version inside the
current file?  I was thinking of just continuing to use the ShellVars lens to
parse the line for the "old version" and tag it the appropriate syntax version
and then write the new one as the default.

-Doug

On 02/11/2012 05:07 PM, Raphaël Pinson wrote:
> After thinking about it some more, I think it could be useful to get
> to a standard using subnodes.
> 
> Here is an example, unrelated to the suggested problem:
> 
> 
> module Migration =
> 
> (* There are 3 possible syntaxes for a line
>    The last one doesn't have a "@syntax" subnode, it's the default -
> newest - syntax *)
> let line = [ key Rx.word .
>              ( (Sep.colon . store Rx.word . [ label "@syntax" . value "1" ])
>              | (Sep.space . store Rx.word . [ label "@syntax" . value "2" ])
>              | (Sep.equal . store Rx.word) )
>              . Util.eol ]
> 
> let lns = line*
> 
> (* Now for some tests *)
> let full = "foo:bar\nfoo=baz\nfoo baa\n"
> 
> (* Get all kind of syntaxes *)
> test lns get full =
>   { "foo" = "bar"
>     { "@syntax" = "1" }
>   }
>   { "foo" = "baz" }
>   { "foo" = "baa"
>     { "@syntax" = "2" }
>   }
> 
> (* Migrate all to new syntax *)
> test lns put full after
>    rm "//@syntax" =
>    "foo=bar\nfoo=baz\nfoo=baa\n"
> 
> (* Force syntax 1 for last entry *)
> test lns put full after
>    set "/foo[3]/@syntax" "1" =
>    "foo:bar\nfoo=baz\nfoo:baa\n"
> 
> 
> 
> Could that be an interesting approach in general?
> 
> Raphaël
> 
> 
> 
> 2012/1/26 Raphaël Pinson <raphink at gmail.com>:
>> Hi Doug,
>>
>> On Thu, Jan 26, 2012 at 4:07 PM, Doug Warner <doug at warner.fm> wrote:
>>> I'm working on a lens to work with Gentoo's new /etc/conf.d/net format and I
>>> realized I need to convert their old format to the new format.
>>>
>>> What's the best way to migrate from one format to another?  I have my lens
>>> mostly working for the new format now, but I realized I might need to parse
>>> both versions; but then I thought that it might not update when augeas
>>> reads/writes the config file.
>>>
>>> I am using puppet to manage these files; so the values are typically set each
>>> run; I'm hoping that would cause augeas to write down the new format rather
>>> than leave it the old version.
>>>
>>> I guess the last option is to wipe out the old file when I upgrade and let
>>> puppet/augeas write down the new file, but that seems painful as well.
>>>
>>> Any recommendations on what to do here?
>>>
>>
>>
>> That's a very interesting question. I see two ways of doing this:
>> * write a single lens which will map both syntaxes to different nodes
>> in the tree, and use the "move" command to migrate;
>> * or write two lenses bound to two different files (file.old and
>> file.new or something similar) and use the "move" command to migrate.
>>
>>
>> Here is a (minimalistic) proof of concept using the first option:
>>
>> $ cat myconfig.aug
>> module MyConfig =
>>
>> autoload xfm
>>
>> let old_record =
>>   let entry = [ Util.del_str "\""
>>               . label "entry"
>>               . store /[0-9.\/]+/
>>               . Util.del_str "\"" ]
>>   in [ label "old_record" . store Rx.word
>>        . Util.del_str "=("
>>        . Build.opt_list entry Sep.space
>>        . Util.del_str ")" . Util.eol ]
>>
>> let new_record =
>>   let entry = [ label "entry"
>>               . store /[0-9.\/]+/ ]
>>   in [ label "new_record" . store Rx.word
>>        . Util.del_str "=\""
>>        . Build.opt_list entry Util.eol
>>        . Util.del_str "\"" . Util.eol ]
>>
>>
>> let lns = old_record | new_record
>>
>> let filter = incl "/file"
>>
>> let xfm = transform lns filter
>>
>> $ cat fakeroot/file
>> config_eth0=("192.168.0.1/24" "192.168.0.2/24")
>>
>> $ augtool -I . -r fakeroot
>> /files
>> /files/file
>> /files/file/old_record = "config_eth0"
>> /files/file/old_record/entry[1] = "192.168.0.1/24"
>> /files/file/old_record/entry[2] = "192.168.0.2/24"
>> rpinson at rpinson:~/bas/augeas_migration$ augtool -I . -r fakeroot/
>> augtool> print /files/
>> /files
>> /files/file
>> /files/file/old_record = "config_eth0"
>> /files/file/old_record/entry[1] = "192.168.0.1/24"
>> /files/file/old_record/entry[2] = "192.168.0.2/24"
>> augtool> mv /files/file/old_record /files/file/new_record
>> augtool> print /files/
>> /files
>> /files/file
>> /files/file/new_record = "config_eth0"
>> /files/file/new_record/entry[1] = "192.168.0.1/24"
>> /files/file/new_record/entry[2] = "192.168.0.2/24"
>> augtool> save
>> Saved 1 file(s)
>>
>> $ cat fakeroot/file
>> config_eth0="192.168.0.1/24
>> 192.168.0.2/24"
>>
>>
>> Note that you can combine this with the -b flag to keep the old version at hand.
>>
>>
>> Raphaël


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