linux-ext4 - Re: [PATCH -v2] ext4: use truncate

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Date:	Tue, 24 May 2011 09:30:02 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	jiayingz@...gle.com
Subject: Re: [PATCH -v2] ext4: use truncate_setsize() unconditionally

On 5/23/11 2:19 PM, Theodore Ts'o wrote:
> In commit c8d46e41 (ext4: Add flag to files with blocks intentionally
> past EOF), if the EOFBLOCKS_FL flag is set, we call ext4_truncate()
> before calling vmtruncate().  This caused any allocated but unwritten
> blocks created by calling fallocate() with the FALLOC_FL_KEEP_SIZE
> flag to be dropped.  This was done to make to make sure that
> EOFBLOCKS_FL would not be cleared while still leaving blocks past
> i_size allocated.  This was not necessary, since ext4_truncate()
> guarantees that blocks past i_size will be dropped, even in the case
> where truncate() has increased i_size before calling ext4_truncate().
> 
> So fix this by removing the EOFBLOCKS_FL special case treatment in
> ext4_setattr().  In addition, use truncate_setsize() followed by a
> call to ext4_truncate() instead of using vmtruncate().  This is more
> efficient since it skips the call to inode_newsize_ok(), which has
> been checked already by inode_change_ok().  This is also in a win in
> the case where EOFBLOCKS_FL is set since it avoids calling
> ext4_truncate() twice.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
>  Jiayingz pointed out that in the case where we fallocate 12k, write 4k, and
>  then truncate to 4k, we should discard the excess fallocate'd blocks.  So if
>  attr->ia_size == inode.i_size, we can skip the truncate_setsize() call, but
>  if the EOFBLOCKS_FL flag is set, we should still call ext4_truncate().

are there xfstests which cover this explicitly?  It should be simple to write.

If filesystem behavior differs we can always make ext4-only tests.

-Eric
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