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From: Nikita Danilov <nikita@clusterfs.com>
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Date: Wed, 22 Jun 2005 18:28:43 +0400
To: David Masover <ninja@slaphack.com>
Cc: Hans Reiser <reiser@namesys.com>, Christoph Hellwig <hch@infradead.org>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       ReiserFS List <reiserfs-list@namesys.com>
Subject: Re: reiser4 plugins
Newsgroups: gmane.comp.file-systems.reiserfs.general,gmane.linux.kernel
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David Masover writes:

[...]

 > 
 > Maintainability is like optimization.  The maintainability of a
 > non-working program is irrelevant.  You'd be right if we already had
 > plugins-in-the-VFS.  We don't.  The most maintainable solution for
 > plugins-in-the-FS that actually exists is Reiser4, exactly as it is now
 > - -- because it is the _only_ one that actually exists right now.

But it is not so. There _are_ plugins-in-the-VFS. VFS operates on opaque
objects (inodes, dentries, file system types) through interfaces:
{inode,address_space,dentry,sb,etc.}_operations. Every file system
back-end if free to implement whatever number of these interfaces. And
the do this already: check the sources; even ext2 does this: e.g.,
ext2_fast_symlink_inode_operations and ext2_symlink_inode_operations.

This is exactly what upper level reiser4 plugins are for.

I guess that one of Christoph Hellwig's complaints is that reiser4
introduces another layer of abstraction to implement something that
already exists.

Nikita.