From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Liu Subject: Re: blkback feature announcement Date: Tue, 08 Dec 2015 09:08:26 +0800 Message-ID: <56662D8A.2050205@oracle.com> References: <566582EC02000078000BC975@prv-mh.provo.novell.com> <56657EA1.5050008@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1a66le-0007Fc-IG for xen-devel@lists.xenproject.org; Tue, 08 Dec 2015 01:08:34 +0000 In-Reply-To: <56657EA1.5050008@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= Cc: xen-devel , Jan Beulich List-Id: xen-devel@lists.xenproject.org On 12/07/2015 08:42 PM, Roger Pau Monn=E9 wrote: > El 07/12/15 a les 13.00, Jan Beulich ha escrit: >> Hello, >> >> is there a particular reason why "max-ring-page-order" gets written in >> xen_blkbk_probe(), but e.g. "feature-max-indirect-segments" and >> "feature-persistent" get written only in connect(), despite both having >> constant values (and hence the node value effectively being known as >> soon as the device exists)? > = > No, AFAIK there's no specific reason. > = AFAIR, that's for the blkfront resume path. We need to get the "max-ring-page-order" in blkfront_resume() in advance, s= o that we can know how many ring pages to be used before setup_blkring(). Bob. >> Or in more general terms: Shouldn't it be well defined at what time >> a frontend can rely on certain nodes to be available for inspection? >> And in doing so, I'd expect the determination to be done such that >> widest flexibility is provided towards the actual implementation, i.e. >> nodes should be written as early as possible. (Of course this applies >> to other frontend/backend pairs too.) > = > I agree. Regarding blkback the nodes about persistent grants, indirect > descriptors and the ring page order should be written in > xen_blkbk_probe, while the specific information about this virtual disk > (sectors, sector size...) should be written before switching to the > connected state (ie: after hotplug scripts have run). > = > Roger. > =