linux-ext4 - Re: [RFC PATCH -next v3 07/10] fs: introduce FALLOC_FL_WRITE

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Message-ID: <20250409103548.GC4950@lst.de>
Date: Wed, 9 Apr 2025 12:35:48 +0200
From: Christoph Hellwig <hch@....de>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-block@...r.kernel.org, dm-devel@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, hch@....de,
	tytso@....edu, djwong@...nel.org, john.g.garry@...cle.com,
	bmarzins@...hat.com, chaitanyak@...dia.com,
	shinichiro.kawasaki@....com, yi.zhang@...wei.com,
	chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [RFC PATCH -next v3 07/10] fs: introduce
 FALLOC_FL_WRITE_ZEROES to fallocate

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.