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Re: [Qemu-devel] [PATCH V6 8/8] block: Use graph node name as reference


From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH V6 8/8] block: Use graph node name as reference in bdrv_file_open().
Date: Fri, 24 Jan 2014 15:48:54 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

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 <address@hidden>
> >>---
> >>  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.

> 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?

Kevin



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