Re: [Qemu-devel] [PATCH 1/3] qmp: Add command 'blockdev-backup'

[Markus Armbruster]

Fam Zheng <address@hidden> writes:

> On Tue, 11/04 07:47, Markus Armbruster wrote:
>> Fam Zheng <address@hidden> writes:
>> 
>> > On Mon, 11/03 15:32, Kevin Wolf wrote:
>> >> Am 03.11.2014 um 02:46 hat Fam Zheng geschrieben:
>> >> > On Fri, 10/31 10:01, Kevin Wolf wrote:
>> >> > > Am 11.09.2014 um 07:05 hat Fam Zheng geschrieben:
>> >> > > > Similar to drive-backup, but this command uses a device id as target
>> >> > > > instead of creating/opening an image file.
>> >> > > > 
>> >> > > > Also add blocker on target bs, since the target is also a
>> >> > > > named device
>> >> > > > now.
>> >> > > > 
>> >> > > > Add check and report error for bs == target which became
>> >> > > > possible but is
>> >> > > > an illegal case with introduction of blockdev-backup.
>> >> > > > 
>> >> > > > Signed-off-by: Fam Zheng <address@hidden>
>> >> > > 
>> >> > > > diff --git a/qapi/block-core.json b/qapi/block-core.json
>> >> > > > index a685d02..b953c7b 100644
>> >> > > > --- a/qapi/block-core.json
>> >> > > > +++ b/qapi/block-core.json
>> >> > > > @@ -669,6 +669,40 @@
>> >> > > >              '*on-target-error': 'BlockdevOnError' } }
>> >> > > >  
>> >> > > >  ##
>> >> > > > +# @BlockdevBackup
>> >> > > > +#
>> >> > > > +# @device: the name of the device which should be copied.
>> >> > > > +#
>> >> > > > +# @target: the name of the backup target device.
>> >> > > 
>> >> > > Both of these are either a BlockBackend ID or a BDS
>> >> > > node-name, right? Do
>> >> > > we have a standard way of expressing this? "name of the device" isn't
>> >> > > quite clear.
>> >> > 
>> >> > "name of the device" is used everywhere to document the "device"
>> >> > parameters in
>> >> > our json schema. Since we have BlockBackend now, device-name
>> >> > and node-name
>> >> > could be better distinguished. All we have to do is giving a
>> >> > beautiful name to
>> >> > both.
>> >> > 
>> >> > [This patch is only a copy&paste and is consistent with the
>> >> > rest part of the
>> >> > file. So I'll leave it for now :]
>> >> 
>> >> The rest of the file doesn't accept node names. But looking at your
>> >> actual code, it seems that you are doing the same (by usign bdrv_find()
>> >> instead of bdrv_lookup_bs()).
>> >
>> > Yes, to be consistent with drive-backup.
>> >
>> >> 
>> >> Shouldn't a proper blockdev-* command accept node names as well?
>> >> 
>> >
>> > I am not sure, it's still blockdev-backup, not blocknode-backup.
>> >
>> > I think that may be another thing, to changed drive-*'s @device
>> > parameter, and
>> > blockdev-*'s @device and @target to accept node names, altogether.
>> 
>> We have many commands identifying nodes by some name: root nodes by BDS
>> device_name[] (now BB name), inner nodes by "file name" (ugh), and
>> arbitrary nodes by BDS name_name[].
>> 
>> An obvious task is deprecating "file name" in favor of node names.
>> 
>> Less obvious is where to accept a node name instead of / in addition to
>> a device name.
>> 
>> Want me to start a thread on this?
>
> Yes please, it's good to review the situation and make some concrete
> convention and plan for the transition.

Done: Review of monitor commands identifying BDS / BB by name