linux-kernel - RE: [PATCH 0/2] Drivers: hv: vmbus: make bus ids in sysfs persistent

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Message-ID: <DM2PR0301MB0783F27B0662F2142112F5E5A0140@DM2PR0301MB0783.namprd03.prod.outlook.com>
Date:	Wed, 17 Aug 2016 16:33:51 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH 0/2] Drivers: hv: vmbus: make bus ids in sysfs persistent



> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Monday, August 15, 2016 9:11 AM
> To: KY Srinivasan <kys@...rosoft.com>
> Cc: devel@...uxdriverproject.org; linux-kernel@...r.kernel.org; Haiyang Zhang
> <haiyangz@...rosoft.com>
> Subject: Re: [PATCH 0/2] Drivers: hv: vmbus: make bus ids in sysfs persistent
> 
> KY Srinivasan <kys@...rosoft.com> writes:
> 
> >> -----Original Message-----
> >> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> >> Sent: Thursday, August 11, 2016 2:17 AM
> >> To: KY Srinivasan <kys@...rosoft.com>
> >> Cc: devel@...uxdriverproject.org; linux-kernel@...r.kernel.org; Haiyang
> Zhang
> >> <haiyangz@...rosoft.com>
> >> Subject: Re: [PATCH 0/2] Drivers: hv: vmbus: make bus ids in sysfs persistent
> >>
> >> KY Srinivasan <kys@...rosoft.com> writes:
> >>
> >> >> -----Original Message-----
> >> >> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> >> >> Sent: Tuesday, August 9, 2016 1:46 AM
> >> >> To: devel@...uxdriverproject.org
> >> >> Cc: linux-kernel@...r.kernel.org; Haiyang Zhang
> >> >> <haiyangz@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>
> >> >> Subject: [PATCH 0/2] Drivers: hv: vmbus: make bus ids in sysfs
> >> >> persistent
> >> >>
> >> >> Bus ids for VMBus devices in /sys/bus/vmbus/devices/ are not
> >> >> guaranteed to be persistent across reboot or kernel restart and this
> >> >> causes problems for some tools. E.g. kexec tools use these ids to identify
> >> NIC on kdump.
> >> >> Fix the issue by using relid from channel offer as the unique id
> >> >> instead of an auto incremented counter.
> >> >
> >> > Relids are not persistent. It is only valid between a channel offer
> >> > message and a relid released message (or an unload or initiate contact
> >> > message, which invalidates all channels). This is an opaque number
> >> > that the root generates and uses to track channels. There is no
> >> > guarantee that the same type of channel (networking, storage, etc)
> >> > will get the same relid on each reboot.
> >> >
> >>
> >> Thanks for the info,
> >>
> >> can we use device_id (offermsg.offer.if_instance.b) instead?
> >
> > I think you could; I am going to verify and get back to you on this.
> 
> Thanks!

The instance GUID is guaranteed to be persistent between boots and also across live migration.

K. Y