linux-ext4 - Re: [RFC][PATCH 7/9]ext4: Add the EXT4_IOC_FIEMAP

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Message-ID: <20081031100547.GA22093@infradead.org>
Date:	Fri, 31 Oct 2008 06:05:47 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andreas Dilger <adilger@....com>
Cc:	Akira Fujita <a-fujita@...jp.nec.com>, linux-ext4@...r.kernel.org,
	Theodore Tso <tytso@....edu>, Mingming Cao <cmm@...ibm.com>
Subject: Re: [RFC][PATCH 7/9]ext4: Add the EXT4_IOC_FIEMAP_INO ioctl

Akira, can you please comment on these issues before going on?
I think the generation issue is a particularly important one if you
want to allow defrag by normal users.

On Sun, Oct 26, 2008 at 04:48:48AM -0400, Christoph Hellwig wrote:
> On Sun, Oct 26, 2008 at 02:40:48AM -0600, Andreas Dilger wrote:
> > This was mentioned last time these patches were posted, but there was
> > no reply from you.  Christoph suggested a more generic VFS open-by-inum,
> > which isn't impossible to do but would cause a lot of controversy I
> > think, while the EXT4_IOC_WRAPPER is at least contained within ext4,
> > but is more generically useful than EXT4_IOC_FIEMAP_INO.
> 
> I'll hack up a generic open_by_handle and then we can gather the
> reaction - it shouldn't be more than about one or two hundred lines of
> code.  Note that you really want an open by handle and not just inum for
> a defragmentation tool - without the generation you can easily run into
> races.
> 
> Btw, any reason the XFS approach of passing in *file descriptors* for both
> the inode to be defragmented and the "donor" inode doesn't work for you?
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