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Date:   Tue, 26 Oct 2021 09:35:44 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 4/8] loop: cover simple read/write via lo_rw_aio()
Message-ID: <20211026073544.GC31967@lst.de>
References: <20211025094437.2837701-1-ming.lei@redhat.com> <20211025094437.2837701-5-ming.lei@redhat.com>
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> -	cmd->iocb.ki_complete = lo_rw_aio_complete;
> -	cmd->iocb.ki_flags = IOCB_DIRECT;
> +
>  	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
> +	if (!cmd->use_dio) {
> +		atomic_set(&cmd->ref, 1);
> +		cmd->iocb.ki_flags = 0;
> +		cmd->ret = lo_call_backing_rw_iter(file, &cmd->iocb, &iter, rw);
> +		lo_rw_aio_do_completion(cmd);
> +		return 0;
> +	}

I don't think we even need the special casing.  If you just use the
AIO path here for buffered I/O it will do the same for you at the
small price of an extra refcount operation.

FYI, this seems to be against a kernel that still has cryptoloop/transfers.