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

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Date:	Thu, 27 Feb 2014 13:03:53 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Namjae Jeon <linkinjeon@...il.com>, 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

2014-02-27 1:48 GMT+09:00, Theodore Ts'o <tytso@....edu>:
> 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.
Okay.

>
>> 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!
Thanks for your review! I will fix these include Hugh's review points.
>
> 					- Ted
>
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