Re: [Nbd] [PATCH 1/2] NBD proto: add WRITE_ZEROES extension
- To: Paolo Bonzini <pbonzini@...696...>
- Cc: nbd-general@lists.sourceforge.net, Kevin Wolf <kwolf@...696...>, qemu-devel@...530..., Stefan Hajnoczi <stefanha@...696...>, "Denis V. Lunev" <den@...2317...>
- Subject: Re: [Nbd] [PATCH 1/2] NBD proto: add WRITE_ZEROES extension
- From: Wouter Verhelst <w@...112...>
- Date: Thu, 24 Mar 2016 13:31:42 +0100
- Message-id: <20160324123142.GF2870@...3...>
- In-reply-to: <56F3D17D.7040100@...696...>
- References: <1458742562-30624-1-git-send-email-den@...2317...> <1458742562-30624-2-git-send-email-den@...2317...> <20160323172116.GA2467@...3...> <20160324075706.GA24831@...2346...> <20160324082641.GF1590@...3...> <56F3D17D.7040100@...696...>
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
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