From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KTLfA-0003qC-Ia for qemu-devel@nongnu.org; Wed, 13 Aug 2008 15:05:40 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KTLf7-0003pr-U9 for qemu-devel@nongnu.org; Wed, 13 Aug 2008 15:05:39 -0400 Received: from [199.232.76.173] (port=47108 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KTLf7-0003pi-N3 for qemu-devel@nongnu.org; Wed, 13 Aug 2008 15:05:37 -0400 Received: from wr-out-0506.google.com ([64.233.184.226]:18793) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KTLf6-0002Rh-VY for qemu-devel@nongnu.org; Wed, 13 Aug 2008 15:05:37 -0400 Received: by wr-out-0506.google.com with SMTP id c46so127829wra.18 for ; Wed, 13 Aug 2008 12:05:33 -0700 (PDT) Message-ID: <48A33057.6010207@codemonkey.ws> Date: Wed, 13 Aug 2008 14:04:55 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] Flush pending AIO on reboot and shutdown. References: <20080813132358.17672.68212.stgit@gleb-debian.qumranet.com.qumranet.com> <48A2E732.4040501@codemonkey.ws> <20080813141346.GC17567@minantech.com> <48A2F89A.20609@codemonkey.ws> <20080813152329.GG17567@minantech.com> <48A30395.6060706@codemonkey.ws> <20080813183544.GA29998@minantech.com> <48A32AA2.6030902@qumranet.com> <20080813185339.GB29998@minantech.com> In-Reply-To: <20080813185339.GB29998@minantech.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Gleb Natapov wrote: > On Wed, Aug 13, 2008 at 09:40:34PM +0300, Avi Kivity wrote: > >> Gleb Natapov wrote: >> >>> but what bother me is that we >>> consciously drop user data that we can easily save. Why? Real HW tries >>> hard to save every bit of user data and we just decided to drop it. The >>> difference between cancel or complete a request may be corrupted or not >>> corrupted file system after a crash. >>> >>> >>> >> If a guest didn't wait for an I/O to complete, it shouldn't expect it to >> be on disk. >> > If you'll save your swiss bank account details in file and suddenly > your guest will crash, you'll surely appreciate if qemu will save it > for you :) > > >> Of course, we can have the IDE layer wait instead of cancelling, which >> will get the request onto the disk. >> >> > That is the current approach, but the wait is done for all block IO not > just IDE. > If the guest hasn't seen confirmation that the data is on disk, as far as the guest is concerned, it's not on disk. If you have a journalled file system, for instance, unless it receives that notification, it's going to replay whatever has happened in the journal since the last successful write operation. Practically speaking, I don't think you're saving data. Regards, Anthony Liguori > -- > Gleb. > > >