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Re: [Qemu-block] [Qemu-devel] [PATCH 3/4] nbd/server: implement dirty bi

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 3/4] nbd/server: implement dirty bitmap export
Date: Wed, 28 Mar 2018 13:08:06 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

22.03.2018 18:26, Vladimir Sementsov-Ogievskiy wrote:
21.03.2018 19:57, Eric Blake wrote:
On 03/21/2018 07:19 AM, Vladimir Sementsov-Ogievskiy wrote:
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>

Rather sparse on the details in the commit message; I had to read the patch to even learn what the new namespace is.

oh, yes, sorry :(

@@ -92,6 +101,7 @@ typedef struct NBDExportMetaContexts {
      bool valid; /* means that negotiation of the option finished without
                     errors */
      bool base_allocation; /* export base:allocation context (block status) */ +    bool dirty_bitmap; /* export qemu-dirty-bitmap:<export_bitmap_name> */

That's a LONG namespace name, and it does not lend itself well to other qemu extensions; so future qemu BLOCK_STATUS additions would require consuming yet another namespace and additional upstream NBD registration.  Wouldn't it be better to have the namespace be 'qemu:' (which we register with upstream NBD just once), where we are then free to document leafnames to look like 'dirty-bitmap:name' or 'foo:bar'?

No doubts. (and this shows, that we may want namespaces in namespaces, so we'll parse ':' anyway).

Only one note here (I'm ashamed): 'qemu-dirty-bitmap' namespace is used in Virtuozzo for the feature, yes, without 'x-' prefix. It's my fault, and it should not influence final solution. The probability of problems is near to zero (especially if we decide now to use 'qemu:' namespace for all qemu-specific things. But I'm not sure about, should we mention this fact in the spec.
[cc NBD list]

Looks like at this point, we can safely move to qemu:dirty-bitmap:name, or any other thing, and we don't need to support my first variant.

Best regards,

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