linux-kernel - Re: [PATCH 12/21] fs: xfs: Introduce FORCEALIGN inode flag

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Message-ID: <20231109152412.GA1521@lst.de>
Date:   Thu, 9 Nov 2023 16:24:12 +0100
From:   Christoph Hellwig <hch@....de>
To:     John Garry <john.g.garry@...cle.com>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org
Subject: Re: [PATCH 12/21] fs: xfs: Introduce FORCEALIGN inode flag

On Fri, Sep 29, 2023 at 10:27:17AM +0000, John Garry wrote:
> From: "Darrick J. Wong" <djwong@...nel.org>
> 
> Add a new inode flag to require that all file data extent mappings must
> be aligned (both the file offset range and the allocated space itself)
> to the extent size hint.  Having a separate COW extent size hint is no
> longer allowed.
> 
> The goal here is to enable sysadmins and users to mandate that all space
> mappings in a file must have a startoff/blockcount that are aligned to
> (say) a 2MB alignment and that the startblock/blockcount will follow the
> same alignment.

This needs a good explanation of why someone would want this.