From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35671) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1anR2N-0002wt-Em for qemu-devel@nongnu.org; Tue, 05 Apr 2016 09:28:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1anR2K-0000ol-OS for qemu-devel@nongnu.org; Tue, 05 Apr 2016 09:28:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57035) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1anR2K-0000oH-Ie for qemu-devel@nongnu.org; Tue, 05 Apr 2016 09:28:52 -0400 References: <56FD7B7E.4060004@redhat.com> <64B326DA-CDF4-4537-B38A-46E7B57C319C@alex.org.uk> <56FD8069.7020101@redhat.com> <56FE26B2.6090903@redhat.com> <20160405050926.GC4183@noname.redhat.com> From: Paolo Bonzini Message-ID: <5703BD8F.1080409@redhat.com> Date: Tue, 5 Apr 2016 15:28:47 +0200 MIME-Version: 1.0 In-Reply-To: <20160405050926.GC4183@noname.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Nbd] Is NBD_CMD_FLAG_FUA valid during NBD_CMD_FLUSH? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: "nbd-general@lists.sourceforge.net" , "qemu-devel@nongnu.org" , Alex Bligh On 05/04/2016 07:09, Kevin Wolf wrote: > > TRIM is an advisory operation, so it doesn't make sense to force access > > to the medium. > > I think it does make sense. It means that on completion there is no > pending discard operation (i.e. either there wasn't a discard or if > there was, it has completed) and other readers will see the final state > of the blocks. This is what already happens though, isn't it? Paolo >> > The closest you could get would be to add FUA to WRITE_ZEROES. But >> > since WRITE_ZEROES is not a particularly common operation there isn't >> > much to gain compared to FLUSHing after the write has completed; in >> > fact SCSI doesn't have a FUA bit on its WRITE SAME command. > Right, I guess this would mostly be for consistency when FUA is > supported more or less everywhere else.