linux-kernel - Re: [PATCH v9 7/8] xfs: support CoW in fsdax mode

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Message-ID: <dfa28f5e-cecb-65c4-23e1-a63ef646d2b0@fujitsu.com>
Date:   Thu, 16 Sep 2021 16:51:48 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Christoph Hellwig <hch@....de>
CC:     <djwong@...nel.org>, <linux-xfs@...r.kernel.org>,
        <dan.j.williams@...el.com>, <david@...morbit.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <nvdimm@...ts.linux.dev>, <rgoldwyn@...e.de>,
        <viro@...iv.linux.org.uk>, <willy@...radead.org>
Subject: Re: [PATCH v9 7/8] xfs: support CoW in fsdax mode



On 2021/9/16 14:23, Christoph Hellwig wrote:
> On Wed, Sep 15, 2021 at 06:45:00PM +0800, Shiyang Ruan wrote:
>> +static int
>> +xfs_dax_write_iomap_end(
>> +	struct inode 		*inode,
>> +	loff_t 			pos,
>> +	loff_t 			length,
>> +	ssize_t 		written,
>> +	unsigned 		flags,
>> +	struct iomap 		*iomap)
>> +{
>> +	struct xfs_inode	*ip = XFS_I(inode);
>> +	/*
>> +	 * Usually we use @written to indicate whether the operation was
>> +	 * successful.  But it is always positive or zero.  The CoW needs the
>> +	 * actual error code from actor().  So, get it from
>> +	 * iomap_iter->processed.
>> +	 */
>> +	const struct iomap_iter *iter =
>> +				container_of(iomap, typeof(*iter), iomap);
>> +
>> +	if (!xfs_is_cow_inode(ip))
>> +		return 0;
>> +
>> +	if (iter->processed <= 0) {
>> +		xfs_reflink_cancel_cow_range(ip, pos, length, true);
>> +		return 0;
>> +	}
>> +
>> +	return xfs_reflink_end_cow(ip, pos, iter->processed);
> 
> Didn't we come to the conflusion last time that we don't actually
> need to poke into the iomap_iter here as the written argument is equal
> to iter->processed if it is > 0:
> 
> 	if (iter->iomap.length && ops->iomap_end) {
> 		ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter),
> 				iter->processed > 0 ? iter->processed : 0,
> 				iter->flags, &iter->iomap);
> 		..
> 
> So should be able to just do:
> 
> static int
> xfs_dax_write_iomap_end(
> 	struct inode 		*inode,
> 	loff_t 			pos,
> 	loff_t 			length,
> 	ssize_t 		written,
> 	unsigned 		flags,
> 	struct iomap 		*iomap)
> {
> 	struct xfs_inode	*ip = XFS_I(inode);
> 
> 	if (!xfs_is_cow_inode(ip))
> 		return 0;
> 
> 	if (!written) {
> 		xfs_reflink_cancel_cow_range(ip, pos, length, true);
> 		return 0;
> 	}
> 
> 	return xfs_reflink_end_cow(ip, pos, written);
> }
> 

I see.  Thanks for your guidance.


--
Ruan