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Re: [PATCH v3 3/3] nbd/server: Allow MULTI_CONN for shared writable expo
From: |
Eric Blake |
Subject: |
Re: [PATCH v3 3/3] nbd/server: Allow MULTI_CONN for shared writable exports |
Date: |
Wed, 16 Mar 2022 16:07:18 -0500 |
User-agent: |
NeoMutt/20211029-454-6adf99 |
On Tue, Mar 15, 2022 at 01:14:41PM +0000, Richard W.M. Jones wrote:
> The patches seem OK to me, but I don't really know enough about the
> internals of qemu-nbd to give a line-by-line review. I did however
> build and test qemu-nbd with the patches:
>
> $ ./build/qemu-nbd /var/tmp/test.qcow2
> $ nbdinfo nbd://localhost
> ...
> can_multi_conn: false
>
>
> $ ./build/qemu-nbd -e 2 /var/tmp/test.qcow2
> $ nbdinfo nbd://localhost
> ...
> can_multi_conn: false
>
> ^^^ Is this expected? It also happens with -e 0.
Yes, because qemu-nbd defaults to read-write connections, but to be
conservative, this patch defaults '-m auto' to NOT advertise
multi-conn for read-write; you need to be explicit:
>
>
> $ ./build/qemu-nbd -e 2 -m on /var/tmp/test.qcow2
> $ nbdinfo nbd://localhost
> ...
> can_multi_conn: true
either with '-m on' as you did here, or with
build/qemu-nbd -r -e 2 /var/tmp/test.qcow2
where the '-m auto' default exposes multi-conn for a readonly client.
>
>
> $ ./build/qemu-nbd -e 2 -m off /var/tmp/test.qcow2
> $ nbdinfo nbd://localhost
> ...
> can_multi_conn: false
>
>
> Rich.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org