linux-kernel - Re: Finding hardlinks

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Date:	Tue, 2 Jan 2007 00:22:54 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Nikita Danilov <nikita@...sterfs.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Benny Halevy <bhalevy@...asas.com>,
	Jan Harkes <jaharkes@...cmu.edu>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	nfsv4@...f.org
Subject: Re: Finding hardlinks

> > BTW. How does ReiserFS find that a given inode number (or object ID in
> > ReiserFS terminology) is free before assigning it to new file/directory?
>
> reiserfs v3 has an extent map of free object identifiers in
> super-block.

Inode free space can have at most 2^31 extents --- if inode numbers 
alternate between "allocated", "free". How do you pack it to superblock?

> reiser4 used 64 bit object identifiers without reuse.

So you are going to hit the same problem as I did with SpadFS --- you 
can't export 64-bit inode number to userspace (programs without 
-D_FILE_OFFSET_BITS=64 will have stat() randomly failing with EOVERFLOW 
then) and if you export only 32-bit number, it will eventually wrap-around 
and colliding st_ino will cause data corruption with many userspace 
programs.

Mikulas
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