linux-kernel - Re: [PATCH v6] ext4: Add support FALLOC_FL_COLLAPSE

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Message-ID: <20140226164827.GB11452@thunk.org>
Date:	Wed, 26 Feb 2014 11:48:28 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	viro@...iv.linux.org.uk, david@...morbit.com, bpm@....com,
	adilger.kernel@...ger.ca, jack@...e.cz, mtk.manpages@...il.com,
	lczerner@...hat.com, linux-fsdevel@...r.kernel.org,
	xfs@....sgi.com, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ashish Sangwan <a.sangwan@...sung.com>
Subject: Re: [PATCH v6] ext4: Add support FALLOC_FL_COLLAPSE_RANGE for
 fallocate

On Mon, Feb 24, 2014 at 10:22:10AM +0900, Namjae Jeon wrote:
> >> +	ret = ext4_es_remove_extent(inode, punch_start,
> >> +				    EXT_MAX_BLOCKS - punch_start - 1);
> >> +	if (ret) {
> >> +		up_write(&EXT4_I(inode)->i_data_sem);
> >> +		goto out_stop;
> >> +	}
> >
> > Doing this at first is probably a bad idea; you should do this at the
> > end, and then completely invalidate the es cache for that inode.  That
> > way, the right thing happens if you get an error in the middle
> > releasing the boxes and shifting the extents:
> Okay, I see.

Actually, thinking about this some more, we do want to do this first,
since if we error out, we do need to make sure the extent cache is
flushed.

> If there is error in the middle of extent shifting, the hole will
> present between the last shifted extent and the extent at which error
> happen so this will be consistent state.
> IMHO even if there is error in between the shift, filesystem will be
> in consistent state.
> Am I missing something?

No, I was wrong about that; you're right.  The file will be in an
inconsistent statement, which will probably be highly confusing for
the application, but the file system will be fine.

So I withdraw my complaints.  I'll do a bit more testing, but so far
the patch looks fine to me.  Thanks for your reply and your work!

					- Ted
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