Re: A couple of questions

["Philipp Gühring" <p.guehring@futureware.at>]

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Dear Hans,

> I am a filesystems developer, and I don't know enough to do more than
> press y with most fscks.  

There is one case, in which I know that I have to say no: If the partition 
that a fsck tries to correct has a different type than the fsck thinks. 
(Running e2fsck against a reiserfs partition for example)

And those things happens when someone changes harddisks, ...

> I think that for the most part, if one is
> going to ask the user to help, one needs to provide a real interface, a
> filesystem structure editor.....  

Well, debugfs (ext2) was an approach into that direction, isn't it?
Now I stumbled across debugreiserfs, but it lacks interactive mode.

> which no FS has ever done....  but
> right now we need to get what we have debugged thoroughly.  It is on the
> list of things I would like to add someday.

What I would like to see is a tool to do the following:
(And I don't think that I will find a sponsor for that tool :-(

After a crash, I make a dd from the crashed partition, into a normal file in 
another partition, that's perhaps on a differnt harddisk.

Then I want to run a dumping utility, that tries to restore every bit that 
still can be found in the crashed partition, and tries to resemble all the 
files in it, and even creating a lost&found directory ...

That dumping utility should take an output directory as argument, in which it 
recreates the contents.

Something like "The Coroners Kit", but more for recovery than for 
investigation.

What is important for that tool:
* It must not crash under any circumstances. Even if every bit of the 
filesystem is currupted, it has to do its work, and try to recover as much as 
possible.
* It has to assume that every bit of the filesystem can be corrupt, so it has 
to try to semantically verify the bits, pointers, ...
* It should try different ways to restore access to lost data, if it stumbles 
across problems in the filesystems.
* There must not be any assertions that would not allow the tool to run over 
the whole partiton, and search everywhere for lost data
* It has to be designed to work on files which are dumps from partition based 
filesystems.
* It should be able to detect and correct common hardware or crash related 
problems in the filesystem: 
  * Files that are not statable or accessible, because there only exists an 
entry in the directory, but nothing in the reiserfs tree
  * Transactions that are open
  * Corrupted directory entries like filenames with special charakters that 
can not be used from the system, or rights with undefined bits, ...
  * ...
* It must not change any data on the partition, instead it writes everything 
to an output directory

Many greetings,
- -- 
~ Philipp Gühring              p.guehring@futureware.at
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