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Re: [Qemu-block] [PATCH 16/22] qmp: add persistent flag to block-dirty-b

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [PATCH 16/22] qmp: add persistent flag to block-dirty-bitmap-add
Date: Mon, 24 Oct 2016 18:12:11 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

10.10.2016 19:08, Max Reitz wrote:
On 30.09.2016 12:53, Vladimir Sementsov-Ogievskiy wrote:


+    }
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 31f9990..2bf56cd 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1235,10 +1235,15 @@
  # @granularity: #optional the bitmap granularity, default is 64k for
  #               block-dirty-bitmap-add
+# @persistent: #optional the bitmap is persistent, i.e. it will be saved to
+#              corresponding block device on it's close. Default is false.
+#              For block-dirty-bitmap-add. (Since 2.8)
I'm not sure what the "For block-dirty-bitmap-add." is supposed to mean,
because this whole struct is for block-dirty-bitmap-add (and for
block-dirty-bitmap-add transactions, to be exact, but @persistent will
surely work there, too, won't it?).

Also, I'd say "will be saved to the corresponding block device image
file" instead of just "block device", because in my understanding a
block device and its image file are two separate things.

Hmm.. But 'its close' is block device close, not file close. And we call common bdrv_* function to save it, so we actually save it to device, and then the device puzzles out, how to actually save it.

  # Since 2.4
  { 'struct': 'BlockDirtyBitmapAdd',
-  'data': { 'node': 'str', 'name': 'str', '*granularity': 'uint32' } }
+  'data': { 'node': 'str', 'name': 'str', '*granularity': 'uint32',
+  '*persistent': 'bool' } }
I think normally we'd align the new line so that the opening ' of
'*persistent' is under the opening ' of 'node'.

  # @block-dirty-bitmap-add
diff --git a/qmp-commands.hx b/qmp-commands.hx
index ba2a916..434b418 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1441,7 +1441,7 @@ EQMP
          .name       = "block-dirty-bitmap-add",
-        .args_type  = "node:B,name:s,granularity:i?",
+        .args_type  = "node:B,name:s,granularity:i?,persistent:b?",
          .mhandler.cmd_new = qmp_marshal_block_dirty_bitmap_add,
@@ -1458,6 +1458,9 @@ Arguments:
  - "node": device/node on which to create dirty bitmap (json-string)
  - "name": name of the new dirty bitmap (json-string)
  - "granularity": granularity to track writes with (int, optional)
+- "persistent": bitmap will be saved to corresponding block device
+                on it's close. Block driver should maintain persistent bitmaps
+                (json-bool, optional, default false) (Since 2.8)
And I don't know what the user is supposed to make of the information
that block drivers will take care of maintaining persistent bitmaps. All
they care about is that it will be stored in the corresponding image
file, so in my opinion it would be better to just omit the last sentence

Users shoud know, that only qcow2 supports persistent bitmaps. Instead of last sentence I can write "For now only Qcow2 disks supports persistent bitmaps".

Best regards,

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