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From: George Dunlap <George.Dunlap@eu.citrix.com>
To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Stefano Stabellini <stefano.stabellini@citrix.com>,
	Anthony Perard <anthony.perard@citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH 5/8] libxl: Share logic for finding path between qemuu and pygrub
Date: Fri, 18 Mar 2016 17:09:13 +0000	[thread overview]
Message-ID: <CAFLBxZYRA_5fewOCpSHKRtOyAQbz1W-z1OCxkejK9WCHDWrdkg@mail.gmail.com> (raw)
In-Reply-To: <22250.62931.365062.452074@mariner.uk.xensource.com>

On Thu, Mar 17, 2016 at 6:22 PM, Ian Jackson <Ian.Jackson@eu.citrix.com> wrote:
> George Dunlap writes ("[PATCH 5/8] libxl: Share logic for finding path between qemuu and pygrub"):
>> From: George Dunlap <george.dunlap@eu.citrix.com>
>
> Thanks.  There are a few format inconsistencies (long lines, spaces)
> which I won't enumerate.
>
>> * In the case of a block script, or a non-dom0 backend, qemuu will now
>> print a warning and skip the disk, rather than adding bogus
>> parameters that will cause qemuu to error out.
>
> I think the consequences here ought to be better spelled out.  AFAICT
> the implication is that, in this case, the disk will be available to
> the guest as a PV disk (because libxl will select a backend other than
> qdisk) but not via the emulated IDE ?
>
> IWBNI the resulting functional restriction were documented, but I
> won't insist on that given that you're improving matters.
>
>> @@ -3023,6 +3024,16 @@ static char * libxl__device_disk_find_local_path(libxl__gc *gc,
>>          goto out;
>>      }
>>
>> +    /*
>> +     * If we're being called for a qemu path, we can pass the target
>> +     * string directly as well
>> +     */
>> +    if (qdisk_direct && disk->backend == LIBXL_DISK_BACKEND_QDISK ) {
>> +        path = libxl__strdup(gc, disk->pdev_path);
>> +        LOG(DEBUG, "Directly accessing local QDISK target %s", path);
>> +        goto out;
>
> Is this really true ?  What if the format is qcow2 ?  I think that
> might result in feeding pygrub the qcow2 file rather than the virtual
> block image it contains.

That's what the "qdisk_direct" argument is for -- it tells
libxl__device_disk_find_local_path, "I can interpret QDISK backends".
Pygrub will call this function with "qdisk_direct" set to "false",
since it can't interpret QDISK backends; this will result in it doing
a local attach instead.

> Overall I think this patch is otherwise probably good but it it's a
> bit hard to see the wood for the trees.  If you felt like factoring
> out some of the refactoring and variable renaming, from the functional
> change, that would be very nice.

Yes, there are a lot of things going on, aren't there.  I think I
remember trying to make it simpler when I first wrote it last year,
but not finding any really sensible in-between points; but I'll give
it another look.

 -George

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  reply	other threads:[~2016-03-18 17:09 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-16 16:09 [PATCH 0/8] tools: Allow HVM domains emulated access to disks provided by hotplug scripts George Dunlap
2016-03-16 16:09 ` [PATCH 1/8] tools/hotplug: Add a "dummy" hotplug script for testing George Dunlap
2016-03-16 16:54   ` Ian Jackson
2016-03-16 16:09 ` [PATCH 2/8] libxl: Remove redundant setting of phyical-device George Dunlap
2016-03-16 16:54   ` Ian Jackson
2016-03-16 16:09 ` [PATCH 3/8] tools/hotplug: Write physical-device-path in addition to physical-device George Dunlap
2016-03-16 16:56   ` Ian Jackson
2016-03-16 16:57     ` George Dunlap
2016-03-16 16:09 ` [PATCH 4/8] libxl: Move check for local access to a funciton George Dunlap
2016-03-16 16:58   ` Ian Jackson
2016-03-16 17:02     ` George Dunlap
2016-03-17 18:11   ` Ian Jackson
2016-03-21 15:35     ` George Dunlap
2016-03-16 16:09 ` [PATCH 5/8] libxl: Share logic for finding path between qemuu and pygrub George Dunlap
2016-03-17 18:22   ` Ian Jackson
2016-03-18 17:09     ` George Dunlap [this message]
2016-04-01 14:17       ` Ian Jackson
2016-03-16 16:09 ` [PATCH 6/8] libxl: Allow local access for block devices with hotplug scripts George Dunlap
2016-03-17 18:36   ` Ian Jackson
2016-03-18 17:17     ` George Dunlap
2016-03-16 16:09 ` [PATCH 7/8] docs: Document block-script protocol George Dunlap
2016-03-16 22:57   ` Jim Fehlig
2016-03-17  9:55     ` George Dunlap
2016-03-17 18:38   ` Ian Jackson
2016-03-16 16:09 ` [PATCH 8/8] DO NOT APPLY libxl: Change hotplug script interface to use physical-device-path George Dunlap

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