xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: "Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>
To: "Durrant, Paul" <pdurrant@amazon.co.uk>
Cc: Michael Brown <mbrown@fensystems.co.uk>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"wei.liu@kernel.org" <wei.liu@kernel.org>,
	Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>,
	Anthony PERARD <anthony.perard@citrix.com>
Subject: Re: [PATCH] xen-netback: Check for hotplug-status existence before watching
Date: Tue, 18 May 2021 12:42:09 +0200	[thread overview]
Message-ID: <YKOaAjdO5H3dRTiK@mail-itl> (raw)
In-Reply-To: <2c23e102b6254e42877eb1e8fe68a4f7@EX13D32EUC003.ant.amazon.com>

[-- Attachment #1: Type: text/plain, Size: 1946 bytes --]

On Tue, May 18, 2021 at 09:48:25AM +0000, Durrant, Paul wrote:
> > -----Original Message-----
> > From: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> > 
> > On Tue, May 18, 2021 at 09:34:45AM +0000, Durrant, Paul wrote:
> > > > -----Original Message-----
> > > > From: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> > > >
> > > > On Tue, May 18, 2021 at 07:57:16AM +0100, Paul Durrant wrote:
> > > > > Why is that missing? We're going behind the back of the toolstack to do the
> > > > > unbind and bind so why should we expect it to re-execute a hotplug script?
> > > >
> > > > Ok, then simply execute the whole hotplug script (instead of its subset)
> > > > after re-loading the backend module and everything will be fine.
> > > >
> > > > For example like this:
> > > >     XENBUS_PATH=backend/vif/$DOMID/$VIF \
> > > >     XENBUS_TYPE=vif \
> > > >     XENBUS_BASE_PATH=backend \
> > > >     script=/etc/xen/scripts/vif-bridge \
> > > >     vif=vif.$DOMID.$VIF \
> > > >     /etc/xen/scripts/vif-bridge online
> > > >
> > >
> > > ... as long as there's no xenstore fall-out that the guest can observe.
> > 
> > Backend will set state to XenbusStateInitWait on load anyway...
> > 
> 
> Oh, that sounds like a bug then... It ought to go straight to connected if the frontend is already there.

To me this sounds very suspicious. But if that's really what should
backend do, then it would "solve" also hotplug-status node issue.
See the end of netback_probe() function.
But I think if you start processing traffic before hotplug script
configures the interface (so - without switching to XenbusStateInitWait
and waiting for hotplug-status node), you'll post some packets into not
enabled interface, which I think will drop them (not queue). TCP will be
fine with that, but many other protocols not.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

      parent reply	other threads:[~2021-05-18 10:42 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-10 18:25 xen-netback hotplug-status regression bug Michael Brown
2021-04-13  7:12 ` Paul Durrant
2021-04-13 10:48   ` Michael Brown
2021-04-13 10:55     ` Paul Durrant
2021-04-13 15:14       ` Michael Brown
2021-04-13 15:25       ` [PATCH] xen-netback: Check for hotplug-status existence before watching Michael Brown
2021-04-13 19:12         ` Paul Durrant
2021-04-13 22:30         ` patchwork-bot+netdevbpf
2021-05-10 18:32         ` Marek Marczykowski-Górecki
2021-05-10 18:47           ` Michael Brown
2021-05-10 18:53             ` Marek Marczykowski-Górecki
2021-05-10 19:06               ` Michael Brown
2021-05-10 19:42                 ` Marek Marczykowski-Górecki
2021-05-11  7:06                   ` Durrant, Paul
2021-05-11 10:40                     ` Marek Marczykowski-Górecki
2021-05-11 10:45                       ` Marek Marczykowski-Górecki
2021-05-11 12:46                         ` Durrant, Paul
2021-05-17 21:43                           ` Marek Marczykowski-Górecki
2021-05-17 21:51                             ` Michael Brown
2021-05-17 21:58                               ` Marek Marczykowski-Górecki
2021-05-18  6:57                             ` Paul Durrant
2021-05-18  9:18                               ` Marek Marczykowski-Górecki
     [not found]                                 ` <887f9533f5c54bfabfbff7231eb99b08@EX13D32EUC003.ant.amazon.com>
     [not found]                                   ` <YKOMpXwcnr9QiXy8@mail-itl>
     [not found]                                     ` <2c23e102b6254e42877eb1e8fe68a4f7@EX13D32EUC003.ant.amazon.com>
2021-05-18 10:42                                       ` Marek Marczykowski-Górecki [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YKOaAjdO5H3dRTiK@mail-itl \
    --to=marmarek@invisiblethingslab.com \
    --cc=anthony.perard@citrix.com \
    --cc=iwj@xenproject.org \
    --cc=mbrown@fensystems.co.uk \
    --cc=netdev@vger.kernel.org \
    --cc=pdurrant@amazon.co.uk \
    --cc=wei.liu@kernel.org \
    --cc=wl@xen.org \
    --cc=xen-devel@lists.xenproject.org \
    --subject='Re: [PATCH] xen-netback: Check for hotplug-status existence before watching' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).