From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Tuesday, December 22, 2020 4:12 PM > > 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. I'm OK with surfacing the hibernation capability via an entry in /sys/bus/vmbus. Correct me if I'm wrong, but I think the concept being surfaced is not "ACPI S4 state" precisely, but slightly more generally whether hibernation is supported for the VM. While those two concepts may be 1:1 for the moment, there might be future configurations where "hibernation is supported" depends on other factors as well. The guidance for things in /sys is that they generally should be single valued (see Documentation/filesystems/sysfs.rst). So my recommendation is to create a "hibernation" entry that has a value of 0 or 1. That's the pattern I see in lots of other places in /sys. If other Hyper-V or VMbus-related features need to be surfaced in the future, they would have their own single-valued entry. Michael > > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > --- > 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 > +Contact: Dexuan Cui <decui@xxxxxxxxxxxxx> > +Description: Features specific to VMs running on Hyper-V > +Users: Daemon that sets up swap partition/file for hibernation > + > What: /sys/bus/vmbus/devices/<UUID>/id > Date: Jul 2009 > KernelVersion: 2.6.31 > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > index d491fdcee61f..958487a40a18 100644 > --- a/drivers/hv/vmbus_drv.c > +++ b/drivers/hv/vmbus_drv.c > @@ -678,6 +678,25 @@ static const struct attribute_group vmbus_dev_group = { > }; > __ATTRIBUTE_GROUPS(vmbus_dev); > > +/* Set up bus attribute(s) for /sys/bus/vmbus/supported_features */ > +static ssize_t supported_features_show(struct bus_type *bus, char *buf) > +{ > + bool hb = hv_is_hibernation_supported(); > + > + return sprintf(buf, "%s\n", hb ? "hibernation" : ""); > +} > + > +static BUS_ATTR_RO(supported_features); > + > +static struct attribute *vmbus_bus_attrs[] = { > + &bus_attr_supported_features.attr, > + NULL, > +}; > +static const struct attribute_group vmbus_bus_group = { > + .attrs = vmbus_bus_attrs, > +}; > +__ATTRIBUTE_GROUPS(vmbus_bus); > + > /* > * vmbus_uevent - add uevent for our device > * > @@ -1024,6 +1043,7 @@ static struct bus_type hv_bus = { > .uevent = vmbus_uevent, > .dev_groups = vmbus_dev_groups, > .drv_groups = vmbus_drv_groups, > + .bus_groups = vmbus_bus_groups, > .pm = &vmbus_pm, > }; > > -- > 2.19.1
