On Mon, 5 Jun 2000, Matt Yourst wrote:
> Here's a thought concerning the on-disk compatibility debate with
> ReiserFS: I was recently in contact with Chris Mason about some
> unrelated issue (i.e., making the ReiserFS timestamp data 64-bit) and
> he noted that ReiserFS's object oriented "item handler" architecture
> makes it fast and safe to update most old filesystem structures to new
> formats on the fly (this includes just about everything from basic
> stuff like stat data to the actual index and directory structures.)
>
Sorry, I can see where you got that from my mail, but it isn't entirely
true. There are 3 basic kinds of metadata. keys, item heads and items.
keys are used to find things in the tree. item heads give information
about items, and items have the real data. The items can be resized at
any time. For example, packed file tails are items. They can be
grown/shrunk as the file size changes, and tree balancing takes care of
putting them in the right block as they change in size. stat data is also
an item, so it can be resized too.
New item types could be added for ACLs (just an example, I'm not trying
to talk abou the right place to do ACLs ;-), or the ACL data
could be appended on the end of the stat data.
But, item heads and keys cannot be resized without a fundamental disk
format change.
-chris
-
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