From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH] blkif.h: enhance comments related to the discard feature Date: Fri, 24 Jan 2014 09:30:28 -0500 Message-ID: <20140124143028.GA12946@phenom.dumpdata.com> References: <1389736679-15637-1-git-send-email-olaf@aepfle.de> <52D955A902000078001149E2@nat28.tlf.novell.com> <20140122211449.GA10426@phenom.dumpdata.com> <52E0DEAC020000780011603E@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1W6hmJ-0008Tr-Il for xen-devel@lists.xenproject.org; Fri, 24 Jan 2014 14:30:39 +0000 Content-Disposition: inline In-Reply-To: <52E0DEAC020000780011603E@nat28.tlf.novell.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: Jan Beulich Cc: xen-devel , Olaf Hering , Keir Fraser List-Id: xen-devel@lists.xenproject.org On Thu, Jan 23, 2014 at 08:19:40AM +0000, Jan Beulich wrote: > >>> On 22.01.14 at 22:14, Konrad Rzeszutek Wilk wrote: > > On Fri, Jan 17, 2014 at 03:09:13PM +0000, Jan Beulich wrote: > >> >>> On 14.01.14 at 22:57, Olaf Hering wrote: > >> > @@ -323,9 +324,14 @@ > >> > * For full interoperability, block front and backends should publish > >> > * identical ring parameters, adjusted for unit differences, to the > >> > * XenStore nodes used in both schemes. > >> > - * (4) Devices that support discard functionality may internally allocate > >> > - * space (discardable extents) in units that are larger than the > >> > - * exported logical block size. > >> > + * (4) Devices that support discard functionality may internally allocate > >> > space > >> > + * (discardable extents) in units that are larger than the exported > >> > logical > >> > + * block size. If the backing device has such discardable extents the > >> > + * backend must provide both discard-granularity and discard-alignment. > > ^^^^ - MAY > > I think the intention is to say that these two should go together, > i.e. specifying just one of them is a mistake. The 'and' in that sentence covers that I think? My reading with 'must' is that 'features-discard' MUST have both discard-granularity and discard-alignment. But that is not the case - even if the device does support them - it does not have to expose them. > > Jan > > >> > + * Backends supporting discard should include discard-granularity and > > ^^^^^ - MAY > >> > + * discard-alignment even if it supports discarding individual sectors. > >> > + * Frontends should assume discard-alignment == 0 and discard-granularity > >> > == > >> > + * sector size if these keys are missing. > >> > * (5) The discard-alignment parameter allows a physical device to be > >> > * partitioned into virtual devices that do not necessarily begin or > >> > * end on a discardable extent boundary. > >