[cap-talk] plash (or bash) and undo/redo

[David-Sarah Hopwood]

John Carlson wrote:
> Since plash replaces glibc with it's own version of glibc to run  
> programs, wouldn't it be possible to add undo, redo, commit, and  
> rollback commands to plash?  I know it would be hard (but not  
> impossible) to undo/redo networking commands, but it seems like you  
> could undo/redo a lot of file system stuff.  For writes, you would do  
> a read first, and store the underlying data being written in an undo  
> object.  For reads, you could reset the file pointer backwards.  You'd  
> have to figure out the opposite of the fcntl and ioctl stuff.  And  
> opens might have to store file system contents for undo as well.   
> tells would keep where they tell'ed from.
> 
> Is this an impossible task, or can we take a hint from the application  
> side that such things are possible, and should be attempted?

It's not an impossible task, but it is a very considerable amount of work,
to put it mildly.

There are existing (experimental) transactional/snapshotting filesystems
that work on Linux, for example Btrfs [*]. It might be a better use of time
and resources, and a better layering of the resulting system, to simply
use such a filesystem "underneath" Plash rather than to attempt to
implement this functionality as part of Plash.


[*] Disclaimer: I do not know much about the design or current status of
    Btrfs.

-- 
David-Sarah Hopwood ⚥