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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: George Dunlap <george.dunlap@citrix.com>
Cc: "Ian Jackson" <ian.jackson@citrix.com>,
	xen-devel@lists.xen.org, "Wei Liu" <wei.liu2@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v2 8/9] docs: Document block-script protocol
Date: Wed, 23 Mar 2016 13:14:24 +0100	[thread overview]
Message-ID: <alpine.OSX.2.20.1603231304040.753@mac> (raw)
In-Reply-To: <56F27BBF.3060702@citrix.com>

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On Wed, 23 Mar 2016, George Dunlap wrote:
> On 22/03/16 12:52, Roger Pau Monné wrote:
> > On Mon, 21 Mar 2016, George Dunlap wrote:
> >> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> >> ---
> >> Changes since v1:
> >> - Attempt to make a clear distinction between custom hotplug scripts
> >> and the script called for raw physical devices and files
> >>
> >> CC: Ian Jackson <ian.jackson@citrix.com>
> >> CC: Wei Liu <wei.liu2@citrix.com>
> >> CC: Roger Pau Monne <roger.pau@citrix.com>
> >> ---
> >>  docs/misc/block-scripts.txt | 101 ++++++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 101 insertions(+)
> >>
> >> diff --git a/docs/misc/block-scripts.txt b/docs/misc/block-scripts.txt
> >> new file mode 100644
> >> index 0000000..6dd5d48
> >> --- /dev/null
> >> +++ b/docs/misc/block-scripts.txt
> >> @@ -0,0 +1,101 @@
> > [...]
> >> +Inputs
> >> +------
> >> +
> >> +In all cases, the scripts are called with either "add" or "remove" as
> >> +the command.  For custom scripts, the command will be the first
> >> +argument of the script (i.e. $1).
> >> +
> >> +The environment variable XENBUS_PATH will be set to the
> >> +path for the block device to be created.
> > 
> > This is true for Linux, but not for NetBSD. On NetBSD no env variables are 
> > needed, and everything is passed as arguments using the following format:
> > 
> > ./<script> <backend_path> <xenbus state>
> > 
> > Where xenbus state is either 2 or 6.
> > 
> > On FreeBSD I'm aiming of using the same input interface for both block and 
> > network scripts, and it is the following:
> > 
> > ./<script> {add/remove} <backend path>
> > 
> > With no env variables provided at all. So either this section is expanded, 
> > or it is labelled as "Linux Inputs".
> 
> Nothing like consistency across implementations. :-)
> 
> So in the case of NetBSD, "2" means 'add' and "6" means 'remove'?  Or
> how does that work?

Yes, 2 means add and 6 remove.
 
> Presumably there's not much we can do about NetBSD at this point, if
> there are (or may be) out-of-tree scripts that expect the new format.
> But unless there's a good reason, it seems like we should try to
> converge the hotplug script protocol.
> 
> Was there a particular reason you wanted to use an argument instead of
> an environment variable?  If not, it's probably better to just follow
> suit with the Linux protocol.

Don't get me wrong, but the Linux protocol is all but consistent :). I'm 
not sure if those other env variables are used by the block hotplug 
scripts, but we also set:

script=<script_name>
XENBUS_TYPE=<vbd/vif>
XENBUS_PATH=<be_path>
XENBUS_BASE_PATH="backend"

And it's even worse for vifs, where the action parameter that we pass to 
the hotplug script is different depending on whether we are dealing with 
a PV or an emulated interface (PV uses "online/offline", while emulated 
use "add/remove").

I would like to share the same interface, but I think the Linux one is 
simply too broken, and I don't want to put this anywhere close to FreeBSD. 
There at least I have a chance of having something that's simple and 
rational.

> If there is a good reason, we could consider changing the Linux protocol
> as well (leaving the environment variable in for backwards-compatibility
> purposes).
> 
>  -George
> 

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  reply	other threads:[~2016-03-23 12:14 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-21 18:16 [PATCH v2 0/9] tools: Allow HVM domains emulated access to disks provided by hotplug scripts George Dunlap
2016-03-21 18:16 ` [PATCH v2 1/9] tools/hotplug: Add a "dummy" hotplug script for testing George Dunlap
2016-03-21 18:16 ` [PATCH v2 2/9] libxl: Remove redundant setting of phyical-device George Dunlap
2016-03-21 18:16 ` [PATCH v2 3/9] tools/hotplug: Write physical-device-path in addition to physical-device George Dunlap
2016-03-21 18:16 ` [PATCH v2 4/9] libxl: Move check for local access to a funciton George Dunlap
2016-03-21 18:16 ` [PATCH v2 5/9] libxl: Rearrange qemu upstream disk argument code George Dunlap
2016-03-21 18:16 ` [PATCH v2 6/9] libxl: Share logic for finding path between qemuu and pygrub George Dunlap
2016-03-22 10:38   ` George Dunlap
2016-03-21 18:16 ` [PATCH v2 7/9] libxl: Allow local access for block devices with hotplug scripts George Dunlap
2016-03-21 18:17 ` [PATCH v2 8/9] docs: Document block-script protocol George Dunlap
2016-03-22 12:52   ` Roger Pau Monné
2016-03-23 11:19     ` George Dunlap
2016-03-23 12:14       ` Roger Pau Monné [this message]
2016-03-24 16:29         ` George Dunlap
2016-03-24 16:51           ` Roger Pau Monné
2016-03-21 18:17 ` [PATCH v2 9/9] DO NOT APPLY libxl: Change hotplug script interface to use physical-device-path George Dunlap
2016-03-23 10:10 ` [PATCH v2 0/9] tools: Allow HVM domains emulated access to disks provided by hotplug scripts Roger Pau Monné
2016-03-23 10:36   ` George Dunlap

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