linux-kernel - Re: [PATCH] blkdev: flush disk cache on ->fsync

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Date:	Mon, 12 Oct 2009 17:06:27 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blkdev: flush disk cache on ->fsync

On Mon, Oct 12 2009, Jeff Moyer wrote:
> Christoph Hellwig <hch@....de> writes:
> 
> > Is anyone going to pick up this patch?
> >
> > On Thu, Aug 20, 2009 at 08:24:32PM +0200, Christoph Hellwig wrote:
> >> Currently there is no barrier support in the block device code.  That
> >> means we cannot guarantee any sort of data integerity when using the
> >> block device node with dis kwrite caches enabled.  Using the raw block
> >> device node is a typical use case for virtualization (and I assume
> >> databases, too).  This patch changes block_fsync to issue a cache flush
> >> and thus make fsync on block device nodes actually useful.
> >> 
> >> Note that in mainline we would also need to add such code to the
> >> ->aio_write method for O_SYNC handling, but assuming that Jan's patch
> >> series for the O_SYNC rewrite goes in it will also call into ->fsync
> >> for 2.6.32.
> >> 
> >> 
> >> Signed-off-by: Christoph Hellwig <hch@....de>
> >> 
> >> 
> >> diff --git a/fs/block_dev.c b/fs/block_dev.c
> >> index 94dfda2..298ad75 100644
> >> --- a/fs/block_dev.c
> >> +++ b/fs/block_dev.c
> >> @@ -398,7 +398,17 @@ static loff_t block_llseek(struct file *file, loff_t offset, int origin)
> >>   
> >>  static int block_fsync(struct file *filp, struct dentry *dentry, int datasync)
> >>  {
> >> -	return sync_blockdev(I_BDEV(filp->f_mapping->host));
> >> +	struct block_device *bdev = I_BDEV(filp->f_mapping->host);
> >> +	int error;
> >> +
> >> +	error = sync_blockdev(bdev);
> >> +	if (error)
> >> +		return error;
> >> +	
> >> +	error = blkdev_issue_flush(bdev, NULL);
> >> +	if (error == -EOPNOTSUPP)
> >> +		error = 0;
> >> +	return error;
> >>  }
> >>  
> >>  /*
> > ---end quoted text---
> 
> Looks ok to me.  Jens?

Yep ditto!

> 
> Acked-by: Jeff Moyer <jmoyer@...hat.com>

-- 
Jens Axboe

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