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Date:   Thu, 29 Oct 2020 07:51:49 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        lining <lining2020x@163.com>, Josef Bacik <josef@toxicpanda.com>,
        Jan Kara <jack@suse.cz>
Subject: Re: [PATCH] nbd: don't update block size after device is started
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On Wed, Oct 28, 2020 at 03:24:34PM +0800, Ming Lei wrote:
> Mounted NBD device can be resized, one use case is rbd-nbd.
> 
> Fix the issue by setting up default block size, then not touch it
> in nbd_size_update() any more. This kind of usage is aligned with loop
> which has same use case too.

I think the only reasonable fix here is to remove the set_blocksize
call entirely.  The concept of block size set by it is a file system
construct and nbd has not business setting it at all.