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

[Eric Blake <eblake@redhat.com>]

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.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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