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SubjectRe: silent semantic changes with reiser4
Christophe Saout wrote:

>Am Donnerstag, den 26.08.2004, 01:45 -0700 schrieb Andrew Morton:
>
>
>
>>And describe the "plugin" system. Why does the filesystem need such a
>>thing (other filesystems get their features via `patch -p1')?
>>
>>
>
>Ok, let me try. (Hans, please don't shoot me if I don't get every detail
>right, I'm trying to simplify and translate)
>
>The reiser4 core is just a big and fast storage layer using a single
>tree. It is bound to a mount point and uses the page cache to manage its
>memory. The only thing it can do on its own is to flush dirty data to
>the disk when the VM wants to (memory pressure) or the VFS wants to
>(unmount, sync) or some "plugin" wants to.
>Additionally it's completely atomic (with respect to crashes, no
>isolation like in databases), comparable to data=journal but without the
>overhead of using a journal for everything.
>
>Up to this point there are no users of this "database" and it does not
>implement any of the VFS methods for a filesystem (except mount and
>unmount perhaps).
>
>All the functionality is provided to
>
^to^via
apologies for the correction but it might confuse some

> the plugins. You can insert,
>remove, lookup or modify key:object pairs (with an index into the
>object). The object
>
^object^item
perform that substitution everywhere in this email

> is a sequence of units. For files a unit would be 1
>byte and the index would be the byte offset. For directories the unit
>would be 1 entry and the index would be the filename.
>
>Now there are some plugins that define how the storage layout on the
>disk is (some kind of "backend" plugins).
>
>*And* there are plugins which are users of the "reiser4 client API" and
>implement the actual VFS methods.
>
>There's a UNIX directory plugin and a UNIX file plugin.
>
>Directories, inodes and file content are just key:object pairs and the
>plugins know how to operate on these.
>
>There's a new plugin in work that also implements UNIX file semantics
>but stores the data for that file encrypted and/or compressed.
>
>These plugins live between the VFS and the storage layer.
>
>Just like the filesystems live between the VFS and the block layer (Hans
>would say that filesystems are VFS plugins ;-)).
>
>
>
>>And what are the licensing implications of plugins? Are they derived
>>works? Must they be GPL'ed?
>>
>>
>
>I suppose yes, at least currently, since they can only be linked with
>reiser4, there's no module infrastructure.
>
>
>

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