linux-kernel - Re: [PATCH] cramfs: generate unique inode number for better inode cache usage

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Message-ID: <1292361878.29621.10.camel@wall-e>
Date:	Tue, 14 Dec 2010 22:24:38 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] cramfs: generate unique inode number for better inode
 cache usage

Am Dienstag, den 14.12.2010, 13:08 -0800 schrieb Linus Torvalds:
> On Tue, Dec 14, 2010 at 12:51 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> >
> > Did you look at using iunique() to generate cramfs inode numbers?
> 
> That breaks the cramfs "hardlinking" (which is just files that have
> the same data pointer), and now a hardlinked file wouldn't have the
> same inode number any more.
> 
> Of course, I'm not sure the hardlinking really matters. cramfs
> hardlinks aren't really traditional hardlinks anyway - since the
> permissions etc are in the directory entry, you can have the data
> hardlinked without having the same permissions, so it's not a "real"
> hardlink even if the inode number were to be the same.
> 

In my opinion hardlinks doesn't matter, because cramfs has no real
hardlinks.

> But this patch seems to roughly approximate the old pseudo-hardlink
> behavior. It used to be that all non-data files showed up with the
> same inode number, now they have separate inode numbers.
> 
> That said, I hate how it moves that "setup_inode" helper function
> inline and then does the "if it's a character device" kinds of tests
> twice. Once for the inode number logic, and once for the inode
> operations structure assignment.
> 
> So I think the approach is fine, but I think the implementation is pretty ugly.
> 

Okay, i will see if i find a better solution. The problem is that the
inode number generation CRAMINO will be called from two different
functions, get_cramfs_inode() and cramfs_readdir(). So it is much more
readable to have one function which creates the inode than an two
optimized implementations.

Stefani


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