Re: [Qemu-devel] [RFC PATCH] rbd: Don't convert keypairs to JSON and back

[Jeff Cody <jcody@redhat.com>]

On Wed, Jul 25, 2018 at 10:56:48AM -0500, Eric Blake wrote:
> On 07/25/2018 10:10 AM, Markus Armbruster wrote:
> >qemu_rbd_parse_filename() builds a keypairs QList, converts it to JSON, and
> >stores the resulting QString in a QDict.
> >
> >qemu_rbd_co_create_opts() and qemu_rbd_open() get the QString from the
> >QDict, pass it to qemu_rbd_set_keypairs(), which converts it back into
> >a QList.
> >
> >Drop both conversions, store the QList instead.
> >
> >This affects output of qemu-img info.  Before this patch:
> >
> >     $ qemu-img info rbd:rbd/testimg.raw:mon_host=192.168.15.180:rbd_cache=true:conf=/tmp/ceph.conf
> >     [junk printed by Ceph library code...]
> >     image: json:{"driver": "raw", "file": {"pool": "rbd", "image": "testimg.raw", "conf": "/tmp/ceph.conf", "driver": "rbd", "=keyvalue-pairs": "[\"mon_host\", \"192.168.15.180\", \"rbd_cache\", \"true\"]"}}
> >     [more output, not interesting here]
> >
> >After this patch, we get
> >
> >     image: json:{"driver": "raw", "file": {"pool": "rbd", "image": "testimg.raw", "conf": "/tmp/ceph.conf", "driver": "rbd", "=keyvalue-pairs": ["mon_host", "192.168.15.180", "rbd_cache", "true"]}}
> >
> >The value of member "=keyvalue-pairs" changes from a string containing
> >a JSON array to that JSON array.  That's an improvement of sorts.  However:
> >
> >* Should "=keyvalue-pairs" even be visible here?  It's supposed to be
> >   purely internal...
> 
> I'd argue that since it is supposed to be internal (as evidenced by the
> leading '=' that does not name a normal variable), changing it doesn't hurt
> stability. But yes, it would be nicer if we could filter it entirely so that
> it does not appear in json: output, if it doesn't truly affect the contents
> that the guest would see.
> 
> >
> >* Is this a stable interface we need to preserve, warts and all?
> 
> I hope not.
> 
> >
> >Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >---
> >  block/rbd.c | 50 ++++++++++++++++++++++----------------------------
> >  1 file changed, 22 insertions(+), 28 deletions(-)
> 
> I'm not yet convinced if we want this patch for 3.0 without more comments
> from the RBD experts, nor do I see too much of an issue if this doesn't go
> in until 3.1.  But as to the code changes itself, I find them nice.

Based on my IRC discussions with Markus, I believe the target for this patch
is indeed 3.1, not 3.0.

> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org
>