linux-kernel - Re: [RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute

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Message-ID: <20250506155515.GL1035866@frogsfrogsfrogs>
Date: Tue, 6 May 2025 08:55:15 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Zhang Yi <yi.zhang@...weicloud.com>, dhowells@...hat.com,
	brauner@...nel.org, 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, tytso@....edu,
	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 v4 07/11] fs: statx add write zeroes unmap attribute

On Tue, May 06, 2025 at 02:10:12PM +0200, Christoph Hellwig wrote:
> On Tue, May 06, 2025 at 07:25:06PM +0800, Zhang Yi wrote:
> > +       if (request_mask & STATX_WRITE_ZEROES_UNMAP &&
> > +           bdev_write_zeroes_unmap(bdev))
> > +               stat->result_mask |= STATX_WRITE_ZEROES_UNMAP;
> 
> That would be my expectation.  But then again this area seems to
> confuse me a lot, so maybe we'll get Christian or Dave to chim in.

Um... does STATX_WRITE_ZEROES_UNMAP protect a field somewhere?
It might be nice to expose the request alignment granularity/max
size/etc.  Or does this flag exist solely to support discovering that
FALLOC_FL_WRITE_ZEROES is supported?  In which case, why not discover
its existence by calling fallocate(fd, WRITE_ZEROES, 0, 0) like the
other modes?

--D