From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52341) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vq0Jf-0004rs-Q0 for qemu-devel@nongnu.org; Mon, 09 Dec 2013 07:52:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Vq0JX-0004XQ-Da for qemu-devel@nongnu.org; Mon, 09 Dec 2013 07:52:03 -0500 Received: from mail-ea0-x231.google.com ([2a00:1450:4013:c01::231]:48867) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vq0JX-0004XI-66 for qemu-devel@nongnu.org; Mon, 09 Dec 2013 07:51:55 -0500 Received: by mail-ea0-f177.google.com with SMTP id n15so1546436ead.36 for ; Mon, 09 Dec 2013 04:51:54 -0800 (PST) Date: Mon, 9 Dec 2013 13:51:48 +0100 From: Stefan Hajnoczi Message-ID: <20131209125148.GD9611@stefanha-thinkpad.redhat.com> References: <1386350580-5666-1-git-send-email-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1386350580-5666-1-git-send-email-kwolf@redhat.com> Subject: Re: [Qemu-devel] [RFC PATCH 00/19] block: Support for 512b-on-4k emulation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, armbru@redhat.com On Fri, Dec 06, 2013 at 06:22:41PM +0100, Kevin Wolf wrote: > This series does not cover 4k guests on a 512 byte host, and I'm not > sure yet what to do with this case. Paolos series contained a patch to > protect against "torn reads" (i.e. reads running in parallel with > writes, which return old data for one half of a sector and new data for > the other half) by serialising requests if the guest block size was > greater than the host block size. > > One problem with this approach is that it assumes that a single host > block size even exists and can be compared against on the top level. > Different backing files can be stored on different storage, though, with > different block sizes. As long as the backing file is read-only you won't get torn reads.