linux-kernel - Re: [PATCH 2/3] fsstack: Generic get/set lower object functions

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Message-ID: <20061103204743.GC16506@filer.fsl.cs.sunysb.edu>
Date:	Fri, 3 Nov 2006 15:47:43 -0500
From:	Josef Sipek <jsipek@....cs.sunysb.edu>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Michael Halcrow <mhalcrow@...ibm.com>,
	Erez Zadok <ezk@...sunysb.edu>,
	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@....linux.org.uk>, Andrew Morton <akpm@...l.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] fsstack: Generic get/set lower object functions

On Thu, Nov 02, 2006 at 11:06:05AM -0500, Trond Myklebust wrote:
> On Wed, 2006-11-01 at 22:59 -0500, Josef Jeff Sipek wrote:
...
> > +static inline struct inode *
> > +__fsstack_lower_inode(struct inode *inode, unsigned long branch_idx)
> > +{
> > +	struct fsstack_inode_info *info = fsstack_inode_data(inode);
> > +		
> > +	return info->inodes[branch_idx];
> > +}
> 
> What is the value of "functions" like the above? They appear just to
> obfuscate the code. Unless your aim is to hide the internals of the
> struct __fsstack_inode_generic_info (sort of futile, since you are
> asking users to include that structure in their private inode structs)
> then it is much more obvious to see what is going on when you write
> 
> 	inode = FSSTACK_I(inode)->inodes[branch];
> 
> rather than
> 
> 	inode = __fsstack_lower_inode(inode, branch);
 
I was thinking about this a bit, and it would seem that not having get/set
function pretty much kills the reson to have generic pointer structures at
all.

Would it make sense to change filesystems like ecryptfs to open-code all
these things instead of using _their own_ get/set functions (e.g.,
ecryptfs_inode_to_lower)?

Other posibility is to move the lower pointers into generic VFS objects in
some clever way (not to waste memory on regular filesystems) - this way, the
stackable filesystems can still share some parts.

Josef "Jeff" Sipek.

-- 
A computer without Microsoft is like chocolate cake without mustard.
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