Message-ID: <45BA1359.7020200@redhat.com>
Date: Fri, 26 Jan 2007 09:42:33 -0500
From: Jeff Layton <jlayton@redhat.com>
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To: Kirill Korotaev <dev@openvz.org>
CC: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] have pipefs ensure i_ino uniqueness by calling iunique
 and hashing the inode
References: <200612291911.kBTJBLvx019107@dantu.rdu.redhat.com> <45B9F939.8070701@openvz.org>
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Kirill Korotaev wrote:
 > Jeff,
 >
 > is 100% uniqeness is so much required for pipe inode numbers?
 > AFAIU, it is not that critical for pipefs (unlike smb, nfs etc.)
 >
 > Thanks,
 > Kirill
 >

There is no in-kernel reason why i_ino uniqueness is important for
pipefs. Where it might matter is userspace. The i_ino value is used for:

1) the st_ino value returned in stat calls

2) the dentry name (generated as "[inode_number]")

So while it's certainly not "correct" to have multiple inodes with the same
number on any filesystem, it is probably more important in some places is
others. For pipefs, maybe it isn't, especially given a potential 6% performance
impact to fix it. Anyone else have thoughts?

-- Jeff

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