Re: [Nbd] [Qemu-devel] [PATCH 3/1] doc: Propose Structured Replies extension
- To: Eric Blake <eblake@...696...>
- Cc: "nbd-general@lists.sourceforge.net" <nbd-general@lists.sourceforge.net>, "qemu-devel@...530..." <qemu-devel@...530...>
- Subject: Re: [Nbd] [Qemu-devel] [PATCH 3/1] doc: Propose Structured Replies extension
- From: Wouter Verhelst <w@...112...>
- Date: Tue, 29 Mar 2016 20:19:49 +0200
- Message-id: <20160329181949.GB12469@...3...>
- In-reply-to: <56FAC47F.9010807@...696...>
- References: <1459173555-4890-1-git-send-email-eblake@...696...> <1459223796-28474-2-git-send-email-eblake@...696...> <55B49D68-2F63-4742-9B60-F6B428ABB3E9@...872...> <56FA8F5B.8060800@...696...> <88E5F63B-B036-45C7-B2FD-B555D54E88F4@...872...> <56FA9B42.2020503@...696...> <08706CF2-6DA1-421E-827D-6C08CC08A9EA@...872...> <56FABF49.8080205@...696...> <20160329180314.GA12469@...3...> <56FAC47F.9010807@...696...>
On Tue, Mar 29, 2016 at 12:07:59PM -0600, Eric Blake wrote:
> On 03/29/2016 12:03 PM, Wouter Verhelst wrote:
> > On Tue, Mar 29, 2016 at 11:45:45AM -0600, Eric Blake wrote:
> >> Supporting DF merely transfers the burden of collection between server
> >> and client. I suspect that there are cases where the server does NOT
> >> want to support DF (because it would require the server to allocate
> >> memory to collect the data before sending a single structured read
> >> reply),
> >
> > There are other ways to handle that; e.g., the server could have a
> > "request too large for non-fragmented read" error message. The spec
> > should give a minimum size that the server MUST support (which should be
> > reasonably large), and should state that a server MAY reply to any
> > request with DF set for a block larger than that minimum, with that
> > error.
>
> How does 64k sound?
Dunno. It might make sense for this number to be based upon some
"standard" minimum request size in things like ATA or SCSI if such a
number exists there, but I don't know enough about either standard to
answer that question myself.
If such a number doesn't exist (or nobody who knows speaks up soon
enough), 64k is certainly good enough, I suppose.
--
< 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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