linux-kernel - Re: [PATCH v3 10/12] xfs: Commit CoW-based atomic writes atomically

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Message-ID: <20250228011304.GC1124788@frogsfrogsfrogs>
Date: Thu, 27 Feb 2025 17:13:04 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: brauner@...nel.org, cem@...nel.org, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	ojaswin@...ux.ibm.com, ritesh.list@...il.com,
	martin.petersen@...cle.com, tytso@....edu,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 10/12] xfs: Commit CoW-based atomic writes atomically

On Thu, Feb 27, 2025 at 06:08:11PM +0000, John Garry wrote:
> When completing a CoW-based write, each extent range mapping update is
> covered by a separate transaction.
> 
> For a CoW-based atomic write, all mappings must be changed at once, so
> change to use a single transaction.
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>

Looks good to me now,
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

--D

> ---
>  fs/xfs/xfs_file.c    |  5 ++++-
>  fs/xfs/xfs_reflink.c | 49 ++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_reflink.h |  3 +++
>  3 files changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 76ea59c638c3..44e11c433569 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -527,7 +527,10 @@ xfs_dio_write_end_io(
>  	nofs_flag = memalloc_nofs_save();
>  
>  	if (flags & IOMAP_DIO_COW) {
> -		error = xfs_reflink_end_cow(ip, offset, size);
> +		if (iocb->ki_flags & IOCB_ATOMIC)
> +			error = xfs_reflink_end_atomic_cow(ip, offset, size);
> +		else
> +			error = xfs_reflink_end_cow(ip, offset, size);
>  		if (error)
>  			goto out;
>  	}
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 97dc38841063..844e2b43357b 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -987,6 +987,55 @@ xfs_reflink_end_cow(
>  		trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
>  	return error;
>  }
> +int
> +xfs_reflink_end_atomic_cow(
> +	struct xfs_inode		*ip,
> +	xfs_off_t			offset,
> +	xfs_off_t			count)
> +{
> +	xfs_fileoff_t			offset_fsb;
> +	xfs_fileoff_t			end_fsb;
> +	int				error = 0;
> +	struct xfs_mount		*mp = ip->i_mount;
> +	struct xfs_trans		*tp;
> +	unsigned int			resblks;
> +
> +	trace_xfs_reflink_end_cow(ip, offset, count);
> +
> +	offset_fsb = XFS_B_TO_FSBT(mp, offset);
> +	end_fsb = XFS_B_TO_FSB(mp, offset + count);
> +
> +	/*
> +	 * Each remapping operation could cause a btree split, so in the worst
> +	 * case that's one for each block.
> +	 */
> +	resblks = (end_fsb - offset_fsb) *
> +			XFS_NEXTENTADD_SPACE_RES(mp, 1, XFS_DATA_FORK);
> +
> +	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
> +			XFS_TRANS_RESERVE, &tp);
> +	if (error)
> +		return error;
> +
> +	xfs_ilock(ip, XFS_ILOCK_EXCL);
> +	xfs_trans_ijoin(tp, ip, 0);
> +
> +	while (end_fsb > offset_fsb && !error) {
> +		error = xfs_reflink_end_cow_extent_locked(tp, ip, &offset_fsb,
> +				end_fsb);
> +	}
> +	if (error) {
> +		trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
> +		goto out_cancel;
> +	}
> +	error = xfs_trans_commit(tp);
> +	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	return error;
> +out_cancel:
> +	xfs_trans_cancel(tp);
> +	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	return error;
> +}
>  
>  /*
>   * Free all CoW staging blocks that are still referenced by the ondisk refcount
> diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
> index dfd94e51e2b4..4cb2ee53cd8d 100644
> --- a/fs/xfs/xfs_reflink.h
> +++ b/fs/xfs/xfs_reflink.h
> @@ -49,6 +49,9 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
>  		xfs_off_t count, bool cancel_real);
>  extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
>  		xfs_off_t count);
> +		int
> +xfs_reflink_end_atomic_cow(struct xfs_inode *ip, xfs_off_t offset,
> +		xfs_off_t count);

Nit: return type should be at column 0 and the name should be right
after.

int xfs_reflink_end_atomic_cow(struct xfs_inode *ip, xfs_off_t offset,
		xfs_off_t count);

With that fixed,
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

--D

>  extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
>  extern loff_t xfs_reflink_remap_range(struct file *file_in, loff_t pos_in,
>  		struct file *file_out, loff_t pos_out, loff_t len,
> -- 
> 2.31.1
>