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Date: Thu, 20 Mar 2025 06:29:29 +0100
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, brauner@kernel.org, djwong@kernel.org,
	cem@kernel.org, dchinner@redhat.com, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	ojaswin@linux.ibm.com, ritesh.list@gmail.com,
	martin.petersen@oracle.com, tytso@mit.edu,
	linux-ext4@vger.kernel.org
Subject: Re: [PATCH v6 10/13] xfs: iomap COW-based atomic write support
Message-ID: <20250320052929.GA12560@lst.de>
References: <20250313171310.1886394-1-john.g.garry@oracle.com> <20250313171310.1886394-11-john.g.garry@oracle.com> <Z9fOoE3LxcLNcddh@infradead.org> <eb7a6175-5637-4ea6-a08c-14776aa67d8b@oracle.com> <20250318053906.GD14470@lst.de> <eff45548-df5a-469b-a4ee-6d09845c86e2@oracle.com> <20250318083203.GA18902@lst.de> <de3f6e25-851a-4ed7-9511-397270785794@oracle.com> <20250319073045.GA25373@lst.de> <ef315f4e-d7e9-48ee-b975-e0a014d10ba2@oracle.com>
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On Wed, Mar 19, 2025 at 10:24:55AM +0000, John Garry wrote:
> it seems to work ok, cheers

Better test it very well, this was really just intended as a sketch..

>> +	count_fsb = end_fsb - offset_fsb;
>> +	resaligned = xfs_aligned_fsb_count(offset_fsb, count_fsb,
>> +			xfs_get_cowextsz_hint(ip));
>> +	xfs_iunlock(ip, XFS_ILOCK_EXCL);
>> +
>> +	error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write,
>> +			XFS_DIOSTRAT_SPACE_RES(mp, resaligned), 0, false, &tp);
>>   	if (error)
>>   		return error;
>>   -	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
>> -			&nimaps, 0);
>> -	if (error)
>> -		goto out_unlock;
>> +	if (!xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &cmap))
>> +		cmap.br_startoff = end_fsb;
>
> Do we really need this logic?
>
> offset_fsb does not change, and logically cmap.br_startoff == end_fsb 
> already, right?

Afte unlocking and relocking the ilock the extent layout could have
changed.