From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MyNEV-0003GJ-J2 for qemu-devel@nongnu.org; Thu, 15 Oct 2009 06:06:55 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MyNEQ-0003D6-RO for qemu-devel@nongnu.org; Thu, 15 Oct 2009 06:06:54 -0400 Received: from [199.232.76.173] (port=35565 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MyNEQ-0003Cv-LD for qemu-devel@nongnu.org; Thu, 15 Oct 2009 06:06:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44360) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MyNEQ-00008c-1T for qemu-devel@nongnu.org; Thu, 15 Oct 2009 06:06:50 -0400 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id n9FA6naX004601 for ; Thu, 15 Oct 2009 06:06:49 -0400 Message-ID: <4AD6F3F5.8000803@redhat.com> Date: Thu, 15 Oct 2009 12:05:41 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] Pass the drive's readonly attribute to the guest OS References: <4AD5F3BD.2040402@redhat.com> <4AD5FEF2.2000308@redhat.com> <4AD6ED3B.1030902@redhat.com> <20091015094331.GE30889@redhat.com> <4AD6F06F.7060209@redhat.com> <20091015095426.GF30889@redhat.com> <4AD6F188.2070103@redhat.com> <20091015100120.GG30889@redhat.com> In-Reply-To: <20091015100120.GG30889@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: Naphtali Sprei , qemu-devel@nongnu.org Am 15.10.2009 12:01, schrieb Gleb Natapov: > On Thu, Oct 15, 2009 at 11:55:20AM +0200, Kevin Wolf wrote: >> Am 15.10.2009 11:54, schrieb Gleb Natapov: >>> On Thu, Oct 15, 2009 at 11:50:39AM +0200, Kevin Wolf wrote: >>>> Am 15.10.2009 11:43, schrieb Gleb Natapov: >>>>> On Thu, Oct 15, 2009 at 11:36:59AM +0200, Kevin Wolf wrote: >>>>>> Am 14.10.2009 18:40, schrieb Naphtali Sprei: >>>>>>> Naphtali Sprei wrote: >>>>>>> >>>>>>>> I'm planning to investigate where qemu should check the read only attribute before exeuting any write command >>>>>>>> to drives, would be sent in a different patch. >>>>>>> >>>>>>> revisiting it, if guest OS knows it's a read only device and tries to modify it, anyhow, we don't really care about error reporting, >>>>>>> as long as qemu doesn't crash (or modify the drive). >>>>>> >>>>>> If the right response to a write on a read-only device is defined in the >>>>>> specification (and it most probably is), we should still give the right >>>>>> response, even though the OS is doing something wrong. >>>>>> >>>>> And since our response to write error may be pausing a VM we shouldn't >>>>> allow this to be triggered by a guest OS. >>>> >>>> I thought we only pause the VM if we get an host IO error? But if you do >>>> want to stop it for all errors, you shouldn't start suppressing errors >>>> so that it doesn't stop. >>>> >>> We pause only on host IO errors, but if we open underlying file as >>> read only (do we?) and try to write into it we will get an IO error >>> in the host. >> >> No, we'll return an error before a write request to the host is even issued. >> > Who is "we"? If "we" == "bdrv_write()/dma_bdrv_write()" then it's all the same. > Upper layers don't actually care why block driver failed. Right, "we" is the qemu block layer. If the devices don't use the error code returned, they better should be fixed, I think? Kevin