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Date: Wed, 9 Apr 2025 12:35:48 +0200
From: Christoph Hellwig <hch@lst.de>
To: Zhang Yi <yi.zhang@huaweicloud.com>
Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
	linux-block@vger.kernel.org, dm-devel@lists.linux.dev,
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	tytso@mit.edu, djwong@kernel.org, john.g.garry@oracle.com,
	bmarzins@redhat.com, chaitanyak@nvidia.com,
	shinichiro.kawasaki@wdc.com, yi.zhang@huawei.com,
	chengzhihao1@huawei.com, yukuai3@huawei.com, yangerkun@huawei.com
Subject: Re: [RFC PATCH -next v3 07/10] fs: introduce
 FALLOC_FL_WRITE_ZEROES to fallocate
Message-ID: <20250409103548.GC4950@lst.de>
References: <20250318073545.3518707-1-yi.zhang@huaweicloud.com> <20250318073545.3518707-8-yi.zhang@huaweicloud.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Mar 18, 2025 at 03:35:42PM +0800, Zhang Yi wrote:
> Users can check the disk support of unmap write zeroes command by
> querying:
> 
>     /sys/block/<disk>/queue/write_zeroes_unmap

No, that is not in any way a good user interface.  Users need to be
able to query this on a per-file basis.

> Finally, this flag should not be specified in conjunction with the
> FALLOC_FL_KEEP_SIZE since allocating written extents beyond file EOF is
> not permitted, and filesystems that always require out-of-place writes
> should not support this flag since they still need to allocated new
> blocks during subsequent overwrites.

Should not or can't?  You're returning an error if this happens, so it
doesn't look like should is the right word here.