Re: [Qemu-devel] [PATCH v4 02/38] blockdev: Allow creation of BDS trees without BB

[Max Reitz]

On 07.09.2015 18:12, Kevin Wolf wrote:
> Am 20.07.2015 um 19:45 hat Max Reitz geschrieben:
>> If the "id" field is missing from the options given to blockdev-add,
>> just omit the BlockBackend and create the BlockDriverState tree alone.
>>
>> However, if "id" is missing, "node-name" must be specified; otherwise,
>> the BDS tree would no longer be accessible.
> 
> We can probably lift this restriction once Jeff's auto-generated ID
> patches are in. However, allowing additional things is easy, so no
> objection here.

Maybe we can lift it, but I don't know. In order to know the node-name,
you'd have to do a query-named-block-nodes before blockdev-add and
another one afterwards, diff it, and thus obtain the ID. But maybe that
doesn't even work, since one blockdev-add operation usually adds
multiple BDSs at ones.

>> Many BDS options which are not parsed by bdrv_open() (like caching)
>> cannot be specified for these BB-less BDS trees yet. A future patch will
>> remove this limitation.
> 
> This makes the command mostly useless, but that's okay.

Well, the future patch is part of this series, so yes, it is okay.

> We'll be working
> on converting flags to QDict options one by one and then it will start
> working.
> 
> There is, however, one flag that doesn't correspond to an option or
> enable an additional feature that is simply missing until then. That one
> worries me a bit: BDRV_O_INCOMING. We should probably include it in this
> patch; or maybe better add another patch before this one which moves the
> setting of BDRV_O_INCOMING from blockdev_init() to bdrv_open_common().

Hm, probably so, yes. It's still missing at the end of this series, too.
However, as far as I can see, O_INCOMING is set only for the root BDS,
so moving it to bdrv_open_common() would probably change behavior,
though maybe that'd be a bug fix, actually.

Max

>> Signed-off-by: Max Reitz <address@hidden>
>> Reviewed-by: Eric Blake <address@hidden>
>> Reviewed-by: Alberto Garcia <address@hidden>
>> ---
>>  blockdev.c                 | 44 +++++++++++++++++++++++++++++++-------------
>>  qapi/block-core.json       | 13 +++++++++----
>>  tests/qemu-iotests/087     |  2 +-
>>  tests/qemu-iotests/087.out |  4 ++--
>>  4 files changed, 43 insertions(+), 20 deletions(-)
> 
> Kevin
>

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