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Re: [Qemu-devel] [for-2.9 8/8] sheepdog: Fix blockdev-add

From: Eric Blake
Subject: Re: [Qemu-devel] [for-2.9 8/8] sheepdog: Fix blockdev-add
Date: Wed, 29 Mar 2017 15:32:28 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 03/29/2017 02:59 PM, Max Reitz wrote:
> On 29.03.2017 18:45, Markus Armbruster wrote:
>> Commit 831acdc "sheepdog: Implement bdrv_parse_filename()" and commit
>> d282f34 "sheepdog: Support blockdev-add" have different ideas on how
>> the QemuOpts parameters for the server address are named.  Fix that.
>> While there, rename BlockdevOptionsSheepdog member addr to server, for
>> consistency with BlockdevOptionsSsh, BlockdevOptionsGluster,
>> BlockdevOptionsNbd.
>> Commit 831acdc's example becomes
>>     --drive driver=sheepdog,server.host=fido,vdi=dolly
>> instead of
>>     --drive driver=sheepdog,host=fido,vdi=dolly
>> Signed-off-by: Markus Armbruster <address@hidden>
>> ---
>>  block/sheepdog.c     | 18 +++++++++---------
>>  qapi/block-core.json |  4 ++--
>>  2 files changed, 11 insertions(+), 11 deletions(-)
> OK, so let me get this straight: Before this patch, @addr was advertised
> as a runtime parameter that actually wasn't supported at all? (Because I
> can't see any place in block/sheepdog.c where it would be parsed.)

Both commits mentioned in the commit message are new to 2.9, so we
aren't breaking any back-compat, but are avoiding cementing in a mistake.

Before this patch, @addr was the QMP spelling (inconsistent with all the
others, where ssh, gluster, and nbd spelled it @server); and because it
was NOT mentioned in the sheepdog.c QemuOpts code, it was impossible to
parse it through -drive.  Which means we have a needless difference
between -drive and -blockdev-add.

After this patch, it is spelled @server for both -drive and
-blockdev-add, and QMP is consistent (both with the QemuOpts code, and
with the other network storage drivers).

> This patch now renames @addr to @server and instead of actually parsing
> the option, it just removes the so-far convenience[1] options @host,
> @port, and @path and just fetches the from @server?

But the convenience options have not been released, so fixing them now
is the right way to go.

> If that is true, I can't say I like it the least. I guess it works for
> 2.9, but there should be a FIXME somewhere in this patch.

A fixme to what? Unlike patch 7/8 which has to deal with legacy -drive
code, here, we have nothing released to break.

> Also, if you set any of server.* in bdrv_parse_filename(), you also have
> to set server.type. It's a SocketAddressFlat, .type is a required field.
> I know it's just for internal use, but that doesn't change the fact that
> it's an invalid SocketAddressFlat object without.

That part's true. Also, you can't set server.host and server.path at the
same time (compare to nbd_process_legacy_socket_options taking pains to
make sure that a valid QAPI object is constructed).

> Max
> [1] Originally there were apparently introduced for
> bdrv_parse_filename() -- but of course you can just use them in -drive
> directly...

There's a difference between the psuedo-file '-drive sheepdog:...'
(where you can use them directly, and that doesn't change in this
patch), and the structured '-drive driver=sheepdog,...' (which didn't
exist before 831acdc, and which we want to match to our QMP).

I'm in favor of this patch, but think you found a real issue with not
constructing a valid qapi object.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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