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

[Jeff Moyer <jmoyer@redhat.com>]

Christoph Hellwig <hch@lst.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@lst.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?

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