linux-ext4 - Re: [PATCH v2 07/11] xfs: iomap CoW-based atomic write support

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Message-ID: <cbccb472-7c01-4aef-bcb6-d303df7b271b@oracle.com>
Date: Tue, 25 Feb 2025 18:07:10 +0000
From: John Garry <john.g.garry@...cle.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: brauner@...nel.org, cem@...nel.org, dchinner@...hat.com, hch@....de,
        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 v2 07/11] xfs: iomap CoW-based atomic write support

On 25/02/2025 17:47, Darrick J. Wong wrote:
>> I can try, and would then need to try to factor out what would be much
>> duplicated code.
> <nod> I think it's pretty straightforward:

Yeah, I already had done sometime like this since.

> 
> xfs_direct_cow_write_iomap_begin()
> {
> 	ASSERT(flags & IOMAP_WRITE);
> 	ASSERT(flags & IOMAP_DIRECT);
> 	ASSERT(flags & IOMAP_ATOMIC_SW);
> 
> 	if (xfs_is_shutdown(mp))
> 		return -EIO;
> 
> 	/*
> 	 * Writes that span EOF might trigger an IO size update on
> 	 * completion, so consider them to be dirty for the purposes of
> 	 * O_DSYNC even if there is no other metadata changes pending or
> 	 * have been made here.
> 	 */
> 	if (offset + length > i_size_read(inode))
> 		iomap_flags |= IOMAP_F_DIRTY;
> 
> 	lockmode = XFS_ILOCK_EXCL;
> 	error = xfs_ilock_for_iomap(ip, flags, &lockmode);
> 	if (error)
> 		return error;
> 
> 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
> 			&imap, &nimaps, 0);
> 	if (error)
> 		goto out_unlock;
> 
> 	error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
> 			&lockmode, true, true);
> 	if (error)
> 		goto out_unlock;
> 
> 	endoff = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount);
> 	trace_xfs_iomap_found(ip, offset, endoff - offset, XFS_COW_FORK,
> 			&cmap);
> 	if (imap.br_startblock != HOLESTARTBLOCK) {

note: As you know, all this is common to xfs_direct_write_iomap_begin(), 
but unfortunately can't neatly be factored out due to the xfs_iunlock() 
calls.

> 		seq = xfs_iomap_inode_sequence(ip, 0);
> 		error = xfs_bmbt_to_iomap(ip, srcmap, &imap, flags, 0,
> 				seq);
> 		if (error)
> 			goto out_unlock;
> 	}
> 	seq = xfs_iomap_inode_sequence(ip, IOMAP_F_SHARED);
> 	xfs_iunlock(ip, lockmode);
> 	return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags,
> 			IOMAP_F_SHARED, seq);
> 
> out_unlock:
> 	if (lockmode)
> 		xfs_iunlock(ip, lockmode);
> 	return error;
> }


Cheers,
John