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

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Date:	Fri, 12 Aug 2016 14:10:05 +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: 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.
Sometime back I removed all the non-determinism in the vmbus device
ID generation. Now, the current scheme of generating the device IDs does
result in persistent IDs across boot (as long as the host presents the devices
to the guest in the same order across boots). Do you have this fix?

Regards,

K. Y
> 
> --
>   Vitaly