linux-kernel - Re: [PATCH RFC 3/8] fs/ext4: Disallow encryption if inode is DAX

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Date:   Wed, 15 Apr 2020 14:02:41 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 3/8] fs/ext4: Disallow encryption if inode is DAX

On Mon 13-04-20 21:00:25, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Encryption and DAX are incompatible.  Changing the DAX mode due to a
> change in Encryption mode is wrong without a corresponding
> address_space_operations update.
> 
> Make the 2 options mutually exclusive by returning an error if DAX was
> set first.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  fs/ext4/super.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0c7c4adb664e..b14863058115 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1325,7 +1325,7 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
>  	if (inode->i_ino == EXT4_ROOT_INO)
>  		return -EPERM;
>  
> -	if (WARN_ON_ONCE(IS_DAX(inode) && i_size_read(inode)))
> +	if (WARN_ON_ONCE(IS_DAX(inode)))

Also here I don't think WARN_ON_ONCE() is warranted once we allow per-inode
setting of DAX. It will then become a regular error condition...

								Honza

>  		return -EINVAL;
>  
>  	res = ext4_convert_inline_data(inode);
> @@ -1349,10 +1349,6 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
>  			ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
>  			ext4_clear_inode_state(inode,
>  					EXT4_STATE_MAY_INLINE_DATA);
> -			/*
> -			 * Update inode->i_flags - S_ENCRYPTED will be enabled,
> -			 * S_DAX may be disabled
> -			 */
>  			ext4_set_inode_flags(inode);
>  		}
>  		return res;
> @@ -1376,10 +1372,6 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
>  				    ctx, len, 0);
>  	if (!res) {
>  		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
> -		/*
> -		 * Update inode->i_flags - S_ENCRYPTED will be enabled,
> -		 * S_DAX may be disabled
> -		 */
>  		ext4_set_inode_flags(inode);
>  		res = ext4_mark_inode_dirty(handle, inode);
>  		if (res)
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR