Re: Authoring a versioning plugin

[Hans Reiser <reiser@namesys.com>]

Yoanis Gil Delgado wrote:

>This are the intentions:
>To write a versioning plugin that will allows the file system user to easily 
>revert the files under versioning to a some previous state.  The plugin will 
>allow to revert the file state, based on revisions number and date 
>modifications(and not sure about this one). There will be a special pseudo 
>file named "previous" that will return the previous version of the file. The 
>final result should allow to the the following actions:
>
>$ echo 1 > myfile.txt  (let's say we make this command at Wed Jan 11 16:53:55)
>$ echo 2 > myfile.txt  (let's say we make this command at Wed Jan 11 16:54:57)
>$ echo 3 >> myfile.txt (let's say we make this command at Wed Jan 11 16:55:59)
>
>Suppose you want the latest version, then you type:
>$ cat myfile/.../previous
>  
>
"...." not "..." ;-)

> Some other content
>Or you want the n-th version, then you type:
>$ cat myfile/.../1
> Some content 
>$ cat myfile/.../2
> Some other content
>$ cat myfile/.../3
> Some other content
> Some more content
>$
>Or the version nearest to some date, then you type:
>$ cat myfile.txt/.../Wed\ Jan\ 11\ 16:50
> Some other content
>
>Also , there will be an special attribute named under_versioning(or something 
>like that), that will tell if the file is under versioning. This plugin will 
>not track directories version, although it's a future plan(I think this 
>should be mixed with some undelete plugin).  
>  
>
How about using myfile/..../1 ;-)

>I'm planning to use a delta techniques for versioning storage (delta 
>compression).
>
Ok, good.

> The versioning will be at the write level.
>
Please make two plugins, one of which is the default, and for which
versioning occurs only when you touch myfile/..../checkin, and the other
occurs with each change.  I am skeptical that having it occur with every
write is desirable actually.

> The versions will be 
>saved in a special directory under the filesystem. I think the hard part is 
>the one related to detecting the changes (a COW it's a possible solution, but 
>i think it's to expensive). I'm thinking a possible solution will be 
>detecting the bytes changing in each write and archiving then as the 
>difference.  This introduce some problems like :
>1-) What happens if the file shrinks?
>2-) What happens if the file grows ?
>  
>
Please consider that myfile/..../checkin will be less work to code.

>I will send another email with a solution to this problems.
>
>I've also plans to extent the documentantion of plugins creation in reiser4 
>with the experiences of this project. I'll be working in this plugin for more 
>than 4 months. If you're interested you're welcome to the the team(just me 
>right now :D )
>
>
>Well....... I think this is all (for now  :D ). Please let me know what you 
>think.
>  
>
This all seems great!

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