From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59923) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1anS0L-0002Xp-HU for qemu-devel@nongnu.org; Tue, 05 Apr 2016 10:30:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1anS0H-00042E-Gr for qemu-devel@nongnu.org; Tue, 05 Apr 2016 10:30:53 -0400 Received: from mail-wm0-x242.google.com ([2a00:1450:400c:c09::242]:34857) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1anS0H-000425-9d for qemu-devel@nongnu.org; Tue, 05 Apr 2016 10:30:49 -0400 Received: by mail-wm0-x242.google.com with SMTP id a140so4840239wma.2 for ; Tue, 05 Apr 2016 07:30:49 -0700 (PDT) Sender: Paolo Bonzini References: <1459858065-13348-1-git-send-email-alex@alex.org.uk> From: Paolo Bonzini Message-ID: <5703CC16.1000002@redhat.com> Date: Tue, 5 Apr 2016 16:30:46 +0200 MIME-Version: 1.0 In-Reply-To: <1459858065-13348-1-git-send-email-alex@alex.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCHv3] Improve the documentation of NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex Bligh , Eric Blake , Wouter Verhelst Cc: "nbd-general@lists.sourceforge.net" , qemu-devel On 05/04/2016 14:07, Alex Bligh wrote: > Improve the documentation of NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA. Specifically > the latter may be set on any command, and its semantics on commands other > than NBD_CMD_WRITE need explaining. Further, explain how these relate to > reordering of commands. > > Signed-off-by: Alex Bligh > --- > doc/proto.md | 51 +++++++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 41 insertions(+), 10 deletions(-) > > ARRRGH - this time with a proper commit header. > > Changes since version 2: > > * Rebase on master > > * Remove bogus 'SHOULD' for FLUSH in relation to writes that are in flight > but not yet completed > > * After consultation with lkml etc., document that FUA on things that do not > write does nothing > > * Document that sending FUA for commands that do nothing is permissible, but > 'SHOULD NOT' be done; an existing client does this. Can you send a pointer to the discussion? FUA on reads definitely does *something* in SCSI (it ensures that the data is moved out of the volatile cache prior to the read, similar to what QEMU implements). Paolo > * Document that FUA on TRIM should do something after all, per Kevin Wolf's > comment