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Message-ID: <026c2c04-aec2-0a8c-ed96-f31ae0918b2e@kernel.dk>
Date:   Sat, 6 Aug 2022 08:51:52 -0600
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Subject: Re: [PATCH RESEND 1/1] loop: introduce LO_FLAGS_NODEALLOC
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To:     Zhang Boyang <zhangboyang.id@gmail.com>,
        Christoph Hellwig <hch@lst.de>, linux-block@vger.kernel.org
Cc:     Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Jan Kara <jack@suse.cz>, Ming Lei <ming.lei@redhat.com>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-kernel@vger.kernel.org
References: <20220806114943.8754-1-zhangboyang.id@gmail.com>
 <20220806114943.8754-2-zhangboyang.id@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <20220806114943.8754-2-zhangboyang.id@gmail.com>
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On 8/6/22 5:49 AM, Zhang Boyang wrote:
> Previously, for file-backed loop devices, REQ_OP_DISCARD and
> REQ_OP_WRITE_ZEROES (without REQ_NOUNMAP) are implemented using
> fallocate(FALLOC_FL_PUNCH_HOLE), which will cause the underlying file to
> be sparse and disk space freed. The users have no choice to prevent this
> this from happening.
> 
> This patch introduces LO_FLAGS_NODEALLOC. With this flag set,
> REQ_OP_DISCARD and REQ_OP_WRITE_ZEROES are forced to use
> fallocate(FALLOC_FL_ZERO_RANGE). The disk space of underlying file is
> kept allocated. This is useful if users, for example, want to use a
> preallocated file as the backing file.

Just in terms of readability, I would prefer if NO_DEALLOC is used
consistently rather than NODEALLOC. The latter reads more like
node-alloc to me.

-- 
Jens Axboe