linux-kernel - Re: [PATCH v6 20/22] ext4: Add DAX functionality

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Date:	Tue, 18 Mar 2014 12:45:29 -0600 (MDT)
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, willy@...ux.intel.com,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v6 20/22] ext4: Add DAX functionality

On Tue, 25 Feb 2014, Matthew Wilcox wrote:
> From: Ross Zwisler <ross.zwisler@...ux.intel.com>
> 
> This is a port of the DAX functionality found in the current version of
> ext2.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>
> [heavily tweaked]
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@...el.com>

...

> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index 594009f..dbdacef 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -686,15 +686,22 @@ retry:
>  			inode_dio_done(inode);
>  			goto locked;
>  		}
> -		ret = __blockdev_direct_IO(rw, iocb, inode,
> -				 inode->i_sb->s_bdev, iov,
> -				 offset, nr_segs,
> -				 ext4_get_block, NULL, NULL, 0);
> +		if (IS_DAX(inode))
> +			ret = dax_do_io(rw, iocb, inode, iov, offset, nr_segs,
> +					ext4_get_block, NULL, 0);
> +		else
> +			ret = __blockdev_direct_IO(rw, iocb, inode,
> +					inode->i_sb->s_bdev, iov, offset,
> +					nr_segs, ext4_get_block, NULL, NULL, 0);
>  		inode_dio_done(inode);
>  	} else {
>  locked:
> -		ret = blockdev_direct_IO(rw, iocb, inode, iov,
> -				 offset, nr_segs, ext4_get_block);
> +		if (IS_DAX(inode))
> +			ret = dax_do_io(rw, iocb, inode, iov, offset, nr_segs,
> +					ext4_get_block, NULL, 0);

We need to pass in a DIO_LOCKING flag to this call to dax_do_io.  This flag is
provided correctly in ext2_direct_IO which is the only other place I found
where we have a call to dax_do_io as an alternative to blockdev_direct_IO.

The other calls to dax_do_io are alternatives to __blockdev_direct_IO, which
has an explicit flags parameter.  I believe all of these cases are being
handled correctly.

- Ross
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