Re: [Qemu-devel] [PATCH V6 8/8] block: Use graph node name as reference in bdrv_file_open().

["Benoît Canet" <benoit.canet@irqsave.net>]

Le Friday 31 Jan 2014 à 21:32:34 (+0100), Max Reitz a écrit :
> On 28.01.2014 01:04, Benoît Canet wrote:
> >Le Monday 27 Jan 2014 à 20:11:59 (+0100), Max Reitz a écrit :
> >>On 27.01.2014 15:36, Benoît Canet wrote:
> >>>Le Friday 24 Jan 2014 à 15:54:39 (+0100), Max Reitz a écrit :
> >>>>On 24.01.2014 15:48, Kevin Wolf wrote:
> >>>>>Am 24.01.2014 um 14:37 hat Max Reitz geschrieben:
> >>>>>>On 24.01.2014 14:26, Kevin Wolf wrote:
> >>>>>>>Am 23.01.2014 um 21:31 hat Benoît Canet geschrieben:
> >>>>>>>>Signed-off-by: Benoit Canet <benoit@irqsave.net>
> >>>>>>>>---
> >>>>>>>>  block.c | 6 +++---
> >>>>>>>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>>>>>I'm not going to merge this one yet. It breaks qemu-iotests case 071,
> >>>>>>>which would have to be adapted.
> >>>>>>>
> >>>>>>>However, first of all I'd like to hear the opinions of at least Eric and
> >>>>>>>Max on what BlockRef should really refer to. I think node names make
> >>>>>>>most sense, but perhaps it's a bit inconvenient and the command line
> >>>>>>>should default to node-name = id when id is set, but node-name isn't?
> >>>>>>The QAPI schema is pretty clear about this: “references the ID of an
> >>>>>>existing block device.”
> >>>>>Sure, that's because I wrote that text before we had a node name.
> >>>>>
> >>>>>However, in 1.7 references didn't work yet, so we still have all freedom
> >>>>>to change the interface as we like.
> >>>>Yes, that's right.
> >>>>
> >>>>>>However, if the ID cannot be found, I think
> >>>>>>we should interpret it as a reference to the node name.
> >>>>>>
> >>>>>>Therefore, I'd first try bdrv_find() and if that returns NULL, try
> >>>>>>again with bdrv_find_node().
> >>>>>I think I would prefer to avoid such ambiguities. Otherwise a management
> >>>>>tool that wants to use the node name needs to check first if it's not
> >>>>>already used as a device name somewhere else and would therefore operate
> >>>>>on the wrong device.
> >>>>>
> >>>>>On the other hand, a management tool using the same names for devices
> >>>>>and nodes just gets what it deserves.
> >>>>>
> >>>>>Perhaps we should use a common namespace for both, i.e. you get an error
> >>>>>if you try to assign a node name that is already a device name and vice
> >>>>>versa?
> >>>>This is what I would go for. However, then I don't really know why
> >>>>we should separate the ID and the node name in the first place
> >>>>(although that's probably because I haven't followed the discussion
> >>>>around node names).
> >>>>
> >>>>Max
> >>>Ping,
> >>>
> >>>I still want to make quorum merge.
> >>>What should be done for the references ?
> >>>
> >>>Best regards
> >>>
> >>>Benoît
> >>My only problem is that I don't really know what IDs are for, then. ;-)
> >>
> > From the understanding I have ID are for block backend top level bds and
> >node-name naming all the bds burried in the graph.
> >
> >So my personal opinion would be to relax the constraint on bdrv_lookup_bs
> >and use it for references.
> >
> >Kevin && Max: what do you think of this scheme ?
> 
> I agree. For example, we could change the constraint to report an
> error only if both ID and node name are actually valid (and point to
> different devices), that is, bdrv_find() and bdrv_find_node() return
> different non-NULL values.

Ok I will write patch doing this on top of quorum patches.

Best regards

Benoît

> 
> Max