Re: [Xen-devel] [PATCH] libxl: stat the path for all non-qdisk backends (including unknown)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-05-10 at 14:55 +0100, George Dunlap wrote:
> On 10/05/13 14:49, Ian Campbell wrote:
> > On Fri, 2013-05-10 at 14:46 +0100, George Dunlap wrote:
> >> On Fri, Apr 26, 2013 at 3:29 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
> >> wrote:
> >>> On Fri, 2013-04-26 at 15:17 +0100, Sylvain Munaut wrote:
> >>>>> Since the intention of that commit was to allow for qdisk backends with 
> >>>>> no
> >>>>> explicit file in dom0 (i.e. network remote backend such as ceph) the 
> >>>>> lowest
> >>>>> impact fix appears to be to make that explicit. This should probably be
> >>>>> revisited to rationalize the probing.
> >>>> What about the remote disk case of blktap ?  blktap2.5 supports NBD
> >>>> already AFAIK
> >>>> and I'm pretty sure I'll hit that same stat issue soon for another
> >>>> remote blktap case.
> >>> Right, sounds like I should have gone with my first instinct which was:
> >>>
> >>> 8<------------------------------------------------------------
> >>>
> >>>  From 884beff4a897d785f61705dcfa2f048536982d7c Mon Sep 17 00:00:00 2001
> >>> From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >>> Date: Fri, 26 Apr 2013 12:41:43 +0100
> >>> Subject: [PATCH] libxl: stat the path for all non-qdisk backends 
> >>> (including unknown)
> >>>
> >>> The commit a8a1f236a296 "libxl: Only call stat() when adding a disk if we
> >>> expect a device to exist." changed things to only stat the file when the 
> >>> phy
> >>> backend was explicitly requested. This broke the case where we are 
> >>> probing and
> >>> would normally be able to decide on the phy option.
> >> So at the moment qdisk backends aren't checked at all with this --
> >> which means that if you give a path to a file that doesn't exist via,
> >> for example, xl cd-insert, things fail in weird ways:
> >>
> >> 1. In qemu-traditional, the command silently completes; the effect is
> >> that the disk currently in the drive is ejected
> >>
> >> 2. in qemu-upstream, qmp returns an error which is reported.  The disk
> >> is ejected from the guest, but the xenstore entries are not updated
> >> (still contain the old values)
> >>
> >> It seems like we should probably also at least check if disk_format is RAW.
> > A kit if these issues will come back with disk driver domains I think.
> >
> >> OTOH, I don't seen an option for disk_format to be ceph; is it just
> >> listed as "raw" as well?  That doesn't seem right...
> > That might well be the correct answer, but not for 4.3 I suspect?
> 
> I can't resolve this into an unambiguous meaning that makes sense. :-)  
> Are you saying that ceph *should* be "raw" long-term, but that it 
> shoudln't be for 4.3?  Or that right now ceph *is* raw, but we should 
> change it for 4.3?  Or that we should change it long-term but leave it 
> for 4.3?

A ceph type might be the correct long term answer, but I don't think we
want to be making that change now, do we?.

Ian.



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