From: Andreas Dilger <adilger@sun.com>
Subject: Re: [PATCH,STABLE 2.6.29 06/18] ext4: Automatically allocate delay
	allocated blocks on close
Date: Wed, 03 Jun 2009 12:14:19 -0600
Message-ID: <20090603181419.GN9002@webber.adilger.int>
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Cc: linux-ext4@vger.kernel.org, stable@kernel.org
To: "Theodore Ts'o" <tytso@mit.edu>
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In-reply-to: <1243944479-20574-6-git-send-email-tytso@mit.edu>
Sender: linux-ext4-owner@vger.kernel.org

On Jun 02, 2009  08:07 -0400, Theodore Ts'o wrote:
> When closing a file that had been previously truncated, force any
> delay allocated blocks that to be allocated so that if the filesystem
> is mounted with data=ordered, the data blocks will be pushed out to
> disk along with the journal commit.  Many application programs expect
> this, so we do this to avoid zero length files if the system crashes
> unexpectedly.
> 
> @@ -3880,6 +3880,9 @@ void ext4_truncate(struct inode *inode)
>  	if (!ext4_can_truncate(inode))
>  		return;
>  
> +	if (inode->i_size == 0)
> +		ei->i_state |= EXT4_STATE_DA_ALLOC_CLOSE;

Since some applications open files with open(..., O_WRONLY|O_CREAT|O_TRUNC)
to avoid re-using existing files (and avoiding the need to check if the
file already exists to modify the flags), it would make sense to set
EXT4_STATE_DA_ALLOC_CLOSE only if the file previously had some data in it.

By the time we get to ext4_truncate() i_size is overwritten already, but
it might make sense to also check i_disksize != 0 before setting this flag.
Otherwise delayed allocation may be inadvertently disabled for these apps
when it should not be.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.