From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43624) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj7a9-0006ou-PW for qemu-devel@nongnu.org; Thu, 24 Mar 2016 11:53:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aj7a5-00045Y-6G for qemu-devel@nongnu.org; Thu, 24 Mar 2016 11:53:57 -0400 Received: from barbershop.grep.be ([89.106.240.122]:34095) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj7a5-00045R-0v for qemu-devel@nongnu.org; Thu, 24 Mar 2016 11:53:53 -0400 Date: Thu, 24 Mar 2016 13:31:42 +0100 From: Wouter Verhelst Message-ID: <20160324123142.GF2870@grep.be> References: <1458742562-30624-1-git-send-email-den@openvz.org> <1458742562-30624-2-git-send-email-den@openvz.org> <20160323172116.GA2467@grep.be> <20160324075706.GA24831@phobos.sw.ru> <20160324082641.GF1590@grep.be> <56F3D17D.7040100@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56F3D17D.7040100@redhat.com> Subject: Re: [Qemu-devel] [Nbd] [PATCH 1/2] NBD proto: add WRITE_ZEROES extension List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: nbd-general@lists.sourceforge.net, Kevin Wolf , qemu-devel@nongnu.org, Pavel Borzenkov , Stefan Hajnoczi , "Denis V. Lunev" On Thu, Mar 24, 2016 at 12:37:33PM +0100, Paolo Bonzini wrote: > > > On 24/03/2016 09:26, Wouter Verhelst wrote: > >> > > >> > No, there is no specific reason. Looks like NBD_CMD_FLAG_ZEROES fits the > >> > spec and implementations nicely. So I'll rewrite the extension and add > >> > the flag instead of the whole command. > > Actually, having given this some more thought... > > > > There is at least one server-side implementation of nbd (mine) which > > silently ignores flags it doesn't know about. This isn't a problem for > > non-critical flags, but it could be a problem for a flag like this. Of > > course, a client shouldn't send a flag to a server which that server > > hasn't heard of, but mistakes do happen. > > > > Do we want to keep that in mind? If so, we might want to keep it as a > > separate command after all. > > > > OTOH, it could be said that silently ignoring unknown messages is a bug. > > I should probably just fix my implementation instead. > > Even if it is a bug, it does suggest that the payload format should not > be changed by flags. For example ignoring flags is a bug for an NBD > server, but not for a Wireshark protocol dissector. Agreed. Let's make this a different command then, instead. -- < ron> I mean, the main *practical* problem with C++, is there's like a dozen people in the world who think they really understand all of its rules, and pretty much all of them are just lying to themselves too. -- #debian-devel, OFTC, 2016-02-12