linux-ext4 - Re: [RFC 6/8] ext4: Add an inode flag for atomic writes

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Message-ID: <ZeYwavaG5WOJTFQ7@dread.disaster.area>
Date: Tue, 5 Mar 2024 07:34:50 +1100
From: Dave Chinner <david@...morbit.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	Ojaswin Mujoo <ojaswin@...ux.ibm.com>, Jan Kara <jack@...e.cz>,
	Theodore Ts'o <tytso@....edu>, Matthew Wilcox <willy@...radead.org>,
	"Darrick J . Wong" <djwong@...nel.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	John Garry <john.g.garry@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 6/8] ext4: Add an inode flag for atomic writes

On Sat, Mar 02, 2024 at 01:12:03PM +0530, Ritesh Harjani (IBM) wrote:
> This patch adds an inode atomic writes flag to ext4
> (EXT4_ATOMICWRITES_FL which uses FS_ATOMICWRITES_FL flag).
> Also add support for setting of this flag via ioctl.
> 
> Co-developed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> ---
>  fs/ext4/ext4.h  |  6 ++++++
>  fs/ext4/ioctl.c | 11 +++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1d2bce26e616..aa7fff2d6f96 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -495,8 +495,12 @@ struct flex_groups {
>  #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
>  /* 0x00400000 was formerly EXT4_EOFBLOCKS_FL */
>  
> +#define EXT4_ATOMICWRITES_FL		FS_ATOMICWRITES_FL /* Inode supports atomic writes */
>  #define EXT4_DAX_FL			0x02000000 /* Inode is DAX */

Tying the on disk format to the kernel user API is a poor choice.
While the flag bits might have the same value, anything parsing the
on-disk format should not be required to include kernel syscall API
header files just to get all the on-disk format definitions it
needs.

-Dave.
-- 
Dave Chinner
david@...morbit.com