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Date:   Tue, 5 Jan 2021 12:58:05 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Dexuan Cui <decui@microsoft.com>
Cc:     wei.liu@kernel.org, kys@microsoft.com, haiyangz@microsoft.com,
        sthemmin@microsoft.com, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, mikelley@microsoft.com,
        vkuznets@redhat.com, marcelo.cerri@canonical.com
Subject: Re: [PATCH] Drivers: hv: vmbus: Add /sys/bus/vmbus/supported_features
Message-ID: <20210105125805.7yypaghcpgafsrcs@liuwe-devbox-debian-v2>
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On Tue, Dec 22, 2020 at 04:12:22PM -0800, Dexuan Cui wrote:
> When a Linux VM runs on Hyper-V, if the host toolstack doesn't support
> hibernation for the VM (this happens on old Hyper-V hosts like Windows
> Server 2016, or new Hyper-V hosts if the admin or user doesn't declare
> the hibernation intent for the VM), the VM is discouraged from trying
> hibernation (because the host doesn't guarantee that the VM's virtual
> hardware configuration will remain exactly the same across hibernation),
> i.e. the VM should not try to set up the swap partition/file for
> hibernation, etc.
> 
> x86 Hyper-V uses the presence of the virtual ACPI S4 state as the
> indication of the host toolstack support for a VM. Currently there is
> no easy and reliable way for the userspace to detect the presence of
> the state (see https://lkml.org/lkml/2020/12/11/1097).  Add
> /sys/bus/vmbus/supported_features for this purpose.
> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>  Documentation/ABI/stable/sysfs-bus-vmbus |  7 +++++++
>  drivers/hv/vmbus_drv.c                   | 20 ++++++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-bus-vmbus b/Documentation/ABI/stable/sysfs-bus-vmbus
> index c27b7b89477c..3ba765ae6695 100644
> --- a/Documentation/ABI/stable/sysfs-bus-vmbus
> +++ b/Documentation/ABI/stable/sysfs-bus-vmbus
> @@ -1,3 +1,10 @@
> +What:		/sys/bus/vmbus/supported_features
> +Date:		Dec 2020
> +KernelVersion:	5.11

Too late for 5.11 now.

Given this is a list of strings, do you want to enumerate them in a
Values section or the Description section?

Wei.