From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33490) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPWl3-0004I0-3A for qemu-devel@nongnu.org; Thu, 04 Sep 2014 09:07:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XPWky-0007i8-ET for qemu-devel@nongnu.org; Thu, 04 Sep 2014 09:07:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31601) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPWky-0007hL-6V for qemu-devel@nongnu.org; Thu, 04 Sep 2014 09:07:20 -0400 Date: Thu, 4 Sep 2014 14:07:14 +0100 From: "Richard W.M. Jones" Message-ID: <20140904130713.GC1302@redhat.com> References: <67d97abc587e7c6985166dbe800686938ac8adb5.1409299732.git.hutao@cn.fujitsu.com> <20140904123522.GH3897@noname.str.redhat.com> <20140904124519.GB1302@redhat.com> <20140904125257.GI3897@noname.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140904125257.GI3897@noname.str.redhat.com> Subject: Re: [Qemu-devel] [PATCH v13 5/6] raw-posix: Add full preallocation option List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Fam Zheng , Hu Tao , qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , Yasunori Goto On Thu, Sep 04, 2014 at 02:52:57PM +0200, Kevin Wolf wrote: > Am 04.09.2014 um 14:45 hat Richard W.M. Jones geschrieben: > > On Thu, Sep 04, 2014 at 02:35:22PM +0200, Kevin Wolf wrote: > > > Please change the code to always write zeros for FULL, > > > > How is this useful for anyone? You don't know if the underlying SAN > > is going to detect these zeroes or combine these blocks together. > > It's just slow for no reason. > > It's slow for the reason that the user has requested it. Do you doubt > that users can know what their backend is doing? Why are you insisting > on providing only the functionality that you personally need? I'm not! I'm trying to make sure we don't end up with a qemu interface which is useless for higher layers. You're proposing preallocation=full which will be slow but not actually give any guarantees, or preallocation=meta which is going to be fast but may not work, and I'm saying that's a dumb interface that's not useful. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW