From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Jackson Subject: Re: [PATCH V4 3/7] libxl: add pvusb API Date: Tue, 16 Jun 2015 12:44:57 +0100 Message-ID: <21888.3129.360614.171879@mariner.uk.xensource.com> References: <1433906441-3280-1-git-send-email-cyliu@suse.com> <1433906441-3280-4-git-send-email-cyliu@suse.com> <557EE03F.5040108@suse.com> <557F18E8.8050305@suse.com> <557FFFA9.2070002@suse.com> <5580064D.10600@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap Cc: Juergen Gross , Wei Liu , Ian Campbell , Chunyan Liu , "xen-devel@lists.xen.org" , Jim Fehlig , Simon Cao List-Id: xen-devel@lists.xenproject.org George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API"): > On Tue, Jun 16, 2015 at 12:19 PM, Juergen Gross wrote: > > I'm pretty sure this is just a matter of timing during boot: the busses > > are all (or at least some of them) queried at the same time and the > > first answering gets number 1, the next 2, and so on. And timing seems > > to be different enough to result in unstable bus numbers. > > Right -- I meant "stable in topology within one boot", but at least > two of you have now understood me to mean "across reboots" by default, > so that's obviously a detail that needs to be specified. :-) I think "stable in topology within one boot" is nearly vacuous (or are we expecting buses or devices to spontaneously renumber themselves for no reason) and also nearly useless. We definitely need _some_ way for a user to identify a specific device uniquely in a way that is reliable from one boot to the next. vid:pid is one way to do this, but not always sufficient. Ian.