From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34651) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj3aC-00087X-IZ for qemu-devel@nongnu.org; Thu, 24 Mar 2016 07:37:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aj3a6-0004Le-Ou for qemu-devel@nongnu.org; Thu, 24 Mar 2016 07:37:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45782) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aj3a6-0004LZ-Jt for qemu-devel@nongnu.org; Thu, 24 Mar 2016 07:37:38 -0400 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> From: Paolo Bonzini Message-ID: <56F3D17D.7040100@redhat.com> Date: Thu, 24 Mar 2016 12:37:33 +0100 MIME-Version: 1.0 In-Reply-To: <20160324082641.GF1590@grep.be> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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: Wouter Verhelst , Pavel Borzenkov Cc: nbd-general@lists.sourceforge.net, "Denis V. Lunev" , Stefan Hajnoczi , qemu-devel@nongnu.org, Kevin Wolf 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. Paolo