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Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconn
From: |
Richard W.M. Jones |
Subject: |
Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection |
Date: |
Wed, 15 Sep 2021 10:00:25 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Sep 15, 2021 at 10:15:20AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 14.09.2021 19:32, Richard W.M. Jones wrote:
> >On Tue, Sep 14, 2021 at 06:21:58PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> >>14.09.2021 17:52, Richard W.M. Jones wrote:
> >>>On the
> >>>server side when the server receives NBD_CMD_DISC it must complete any
> >>>in-flight requests, but there's no requirement for the server to
> >>>commit anything to disk. IOW you can still lose data even though you
> >>>took the time to disconnect.
> >>>
> >>>So I don't think there's any reason for libnbd to always gracefully
> >>
> >>Hmm. Me go to NBD spec :)
> >>
> >>I think, there is a reason:
> >>
> >>"The client and the server MUST NOT initiate any form of disconnect other
> >>than in one of the above circumstances."
> >>
> >>And the only possibility for client to initiate a hard disconnect listed
> >>above is "if it detects a violation by the other party of a mandatory
> >>condition within this document".
> >>
> >>So at least, nbdsh violates NBD protocol. May be spec should be updated to
> >>satisfy your needs.
> >
> >I would say the spec is at best contradictory, but if you read other
> >parts of the spec, then it's pretty clear that we're allowed to drop
> >the connection whenever we like. This section says as much:
> >
> >https://github.com/NetworkBlockDevice/nbd/blob/5805b25ad3da96e7c0b3160cda51ea19eb518d5b/doc/proto.md#terminating-the-transmission-phase
>
> Hmm, that was exactly the section I read and quoted :)
>
> >
> > There are two methods of terminating the transmission phase:
> > ...
> > "The client or the server drops the TCP session (in which case it
> > SHOULD shut down the TLS session first). This is referred to as
> > 'initiating a hard disconnect'."
>
> Right. Here the method is defined, no word that client can do it at any time.
I don't read this as a definition.
But we should probably clarify the spec to note that dropping the
connection is fine, because it is - no one has made any argument so
far that there's an actual reason to waste time on NBD_CMD_DISC.
Rich.
> Next, in same section:
>
> Either side MAY initiate a hard disconnect if it detects a violation by
> the other party of a mandatory condition within this document.
>
> Next
> The client MAY issue a soft disconnect at any time
>
> And finally:
>
> The client and the server MUST NOT initiate any form of disconnect other
> than in one of the above circumstances.
>
>
> Or do you mean some other spec section I missed?
>
> >
> >Anyway we're dropping the TCP connection because sometimes we are just
> >interrogating an NBD server eg to find out what it supports, and doing
> >a graceful shutdown is a waste of time and internet.
> >
> >>>shut down (especially in this case where there are no in-flight
> >>>requests), and anyway it would break ABI to make that change and slow
> >>>down the client in cases when there's nothing to clean up.
> >>
> >>Which ABI will it break?
> >
> >Our contract with callers using nbd_close(3), if nbd_shutdown(3) is
> >not called beforehand.
> >https://libguestfs.org/nbd_shutdown.3.html
> >https://libguestfs.org/nbd_create.3.html (really nbd_close ...)
> >
> >Rich.
> >
>
>
> --
> Best regards,
> Vladimir
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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- [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Richard W.M. Jones, 2021/09/13
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Vladimir Sementsov-Ogievskiy, 2021/09/14
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Richard W.M. Jones, 2021/09/14
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Vladimir Sementsov-Ogievskiy, 2021/09/14
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Richard W.M. Jones, 2021/09/14
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Vladimir Sementsov-Ogievskiy, 2021/09/15
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection,
Richard W.M. Jones <=
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Vladimir Sementsov-Ogievskiy, 2021/09/15
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Eric Blake, 2021/09/17
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Eric Blake, 2021/09/17
- Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Eric Blake, 2021/09/14
Re: [PATCH v2] nbd/server: Suppress Broken pipe errors on abrupt disconnection, Eric Blake, 2021/09/14