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Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements

From Christoph Hellwig <hch@infradead.org>
Newsgroups linux.kernel
Subject Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements
Date 2016-09-15 14:20 +0200
Message-ID <shDO3-6VP-37@gated-at.bofh.it> (permalink)
References (2 earlier) <shCyC-5VC-15@gated-at.bofh.it> <shDl0-6rX-13@gated-at.bofh.it> <shDuG-6vN-55@gated-at.bofh.it> <shDEm-6P5-45@gated-at.bofh.it> <shDO2-6VP-29@gated-at.bofh.it>
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On Thu, Sep 15, 2016 at 01:11:24PM +0100, Alex Bligh wrote:
> > NBD_CMD_FLUSH (3)
> > 
> > A flush request; a write barrier. 
> 
> I can see that's potentially confusing as isn't meant to mean 'an old-style
> linux kernel block device write barrier'. I think in general terms it
> probably is some form of barrier, but I see no problem in deleting the
> words "a write barrier" from the spec text if only to make it
> clearer.

Yes, please do that.  A "barrier" implies draining of the queue.

> However, I think the description of the command itself:
> 
> > The server MUST NOT send a successful reply header for this request before all write requests for which a reply has already been sent to the client have reached permanent storage (using fsync() or similar).
> 
> and the ordering section I pointed you to before, were both correct, yes?

Yes, this seems correct.

> actually fdatasync() technically does more than is necessary, as it
> will also flush commands that have been processed, but for which no
> reply has yet been sent - that's no bad thing.

Yes.  But without an actual barrier it's hard to be exact - and
fdatasync does the right thing by including false positives.

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Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-09 22:20 +0200
  Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-09 23:00 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Jens Axboe <axboe@kernel.dk> - 2016-09-10 01:40 +0200
  Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 13:00 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 13:20 +0200
      Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 13:40 +0200
        Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 13:50 +0200
          Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 13:50 +0200
            Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:00 +0200
              Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 14:10 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:30 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:30 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 14:30 +0200
              Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:10 +0200
      Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 13:40 +0200
      Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Eric Blake <eblake@redhat.com> - 2016-09-15 15:40 +0200
        Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Paolo Bonzini <pbonzini@redhat.com> - 2016-09-15 16:10 +0200
          Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 17:30 +0200
            Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Paolo Bonzini <pbonzini@redhat.com> - 2016-09-15 23:20 +0200
        Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 17:30 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 13:50 +0200
      Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:00 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 13:50 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 14:00 +0200
      Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:10 +0200
        Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:20 +0200
          Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:20 +0200
            Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:30 +0200
        Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 14:30 +0200
          Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:30 +0200
            Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:40 +0200
              Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:40 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:50 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 14:50 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 15:20 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 17:20 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 18:10 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Wouter Verhelst <w@uter.be> - 2016-09-15 18:30 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Alex Bligh <alex@alex.org.uk> - 2016-09-15 18:50 +0200
                Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Eric Blake <eblake@redhat.com> - 2016-09-15 21:10 +0200
              Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:40 +0200
    Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Christoph Hellwig <hch@infradead.org> - 2016-09-15 14:20 +0200

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