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Subject: Re: [PATCH 4/4] iomap: cleanup iomap_write_iter()
To: "Darrick J. Wong" <djwong@kernel.org>,
 Christoph Hellwig <hch@infradead.org>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-kernel@vger.kernel.org, brauner@kernel.org, david@fromorbit.com,
 tytso@mit.edu, jack@suse.cz, yi.zhang@huawei.com, chengzhihao1@huawei.com,
 yukuai3@huawei.com
References: <20240311122255.2637311-1-yi.zhang@huaweicloud.com>
 <20240311122255.2637311-5-yi.zhang@huaweicloud.com>
 <20240311160739.GV1927156@frogsfrogsfrogs> <ZfBJYG5OHgLGewHv@infradead.org>
 <20240312162729.GD1927156@frogsfrogsfrogs>
From: Zhang Yi <yi.zhang@huaweicloud.com>
Message-ID: <72683844-f2df-9773-bfb8-7dc2bff76272@huaweicloud.com>
Date: Wed, 13 Mar 2024 17:23:38 +0800
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On 2024/3/13 0:27, Darrick J. Wong wrote:
> On Tue, Mar 12, 2024 at 05:24:00AM -0700, Christoph Hellwig wrote:
>> On Mon, Mar 11, 2024 at 09:07:39AM -0700, Darrick J. Wong wrote:
>>> If at some point iomap_write_end actually starts returning partial write
>>> completions (e.g. you wrote 250 bytes, but for some reason the pagecache
>>> only acknowledges 100 bytes were written) then this code no longer
>>> reverts the iter or truncates posteof pagecache correctly...
>>
>> I don't think it makes sense to return a partial write from
>> iomap_write_end.  But to make that clear it really should not return
>> a byte count by a boolean.  I've been wanting to make that cleanup
>> for a while, but it would reach all the way into buffer.c.
> 
> For now, can we change the return types of iomap_write_end_inline and
> __iomap_write_end?  Then iomap can WARN_ON if the block_write_end return
> value isn't 0 or copied:
> 
> 	bool ret;
> 
> 	if (srcmap->type == IOMAP_INLINE) {
> 		ret = iomap_write_end_inline(iter, folio, pos, copied);
> 	} else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
> 		size_t bh_written;
> 
> 		bh_written = block_write_end(NULL, iter->inode->i_mapping,
> 				pos, len, copied, &folio->page, NULL);
> 
> 		WARN_ON(bh_written != copied && bh_written != 0);
> 		ret = bh_written == copied;
> 	} else {
> 		ret = __iomap_write_end(iter->inode, pos, len, copied, folio);
> 	}
> 
> 	...
> 
> 	return ret;
> 
> Some day later we can circle back to bufferheads, or maybe they'll die
> before we get to it. ;)
> 

It looks great to me for now, we can revise iomap first.

Thanks,
Yi.