linux-kernel - Re: [PATCH] nbd: add support for rotational devices

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Message-ID: <xdq3z4oosh2l4hzlkgxsfbqza6z2q2c2zyznmo24rtt6svlixr@c2w2tpzqlzbp>
Date: Thu, 25 Jul 2024 13:30:35 -0500
From: Eric Blake <eblake@...hat.com>
To: Wouter Verhelst <w@...r.be>
Cc: Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>, 
	linux-block@...r.kernel.org, nbd@...er.debian.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nbd: add support for rotational devices

On Thu, Jul 25, 2024 at 06:45:36PM GMT, Wouter Verhelst wrote:
> The NBD protocol defines the flag NBD_FLAG_ROTATIONAL to flag that the
> export in use should be treated as a rotational device.
> 
> Add support for that flag to the kernel driver.
> 
> Signed-off-by: Wouter Verhelst <w@...r.be>
> ---
>  drivers/block/nbd.c      | 3 +++
>  include/uapi/linux/nbd.h | 3 ++-
>  2 files changed, 5 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@...hat.com>

For what it's worth, the nbdkit project recently made it possible to
aad a filter on top of any existing NBD server to change the setting
of the rotational bit[1], as well as a filter to intentionally
simulate delays of a rotational device[2], in order to experiment with
how much impact changing the bit can have when it is not ignored.

[1] https://libguestfs.org/nbdkit-rotational-filter.1.html
[2] https://libguestfs.org/nbdkit-spinning-filter.1.html

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org