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Re: [Qemu-devel] [PATCH v5 6/6] docs/interop: add nbd.txt

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v5 6/6] docs/interop: add nbd.txt
Date: Wed, 20 Jun 2018 06:33:34 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 06/09/2018 10:17 AM, Vladimir Sementsov-Ogievskiy wrote:
Describe new metadata namespace: "qemu".

Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
  docs/interop/nbd.txt | 37 +++++++++++++++++++++++++++++++++++++
  MAINTAINERS          |  1 +
  2 files changed, 38 insertions(+)
  create mode 100644 docs/interop/nbd.txt

diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
new file mode 100644
index 0000000000..7366269fc0
--- /dev/null
+++ b/docs/interop/nbd.txt
@@ -0,0 +1,37 @@
+Qemu supports NBD protocol, and has internal NBD client (look at

s/supports/supports the/

+block/nbd.c), internal NBD server (look at blockdev-nbd.c) as well as

s/internal/an internal/2

+external NBD server tool - qemu-nbd.c. The common code is placed in

s/external/an external/

+NBD protocol is specified here:

s/NBD/The NBD/

+This following paragraphs describe some specific properties of NBD
+protocol realization in Qemu.
+= Metadata namespaces =
+Qemu supports "base:allocation" metadata context as defined in the NBD

s/supports/supports the/

+protocol specification and defines own metadata namespace: "qemu".

s/own/an additional/

+== "qemu" namespace ==
+For now, the only type of metadata context in the namespace is dirty
+bitmap. All available metadata contexts have the following form:


The "qemu" namespace currently contains only one type of context, related to exposing the contents of a dirty bitmap alongside the associated disk contents. The available metadata context has the following form:

+   qemu:dirty-bitmap:<dirty-bitmap-export-name>
+Each dirty-bitmap metadata context defines the only one flag for
+extents in reply for NBD_CMD_BLOCK_STATUS:
+    bit 0: NBD_STATE_DIRTY, means that the extent is "dirty"
+For NBD_OPT_LIST_META_CONTEXT the following queries are supported
+additionally to "qemu:dirty-bitmap:<dirty-bitmap-export-name>":

s/additionally/in addition/

+* "qemu:" : returns list of all available metadata contexts in the
+            namespace.
+* "qemu:dirty-bitmap:" : returns list of all available dirty-bitmap
+                         metadata contexts.
index e187b1f18f..887b479440 100644
@@ -1923,6 +1923,7 @@ F: nbd/
  F: include/block/nbd*
  F: qemu-nbd.*
  F: blockdev-nbd.c
+F: docs/interop/nbd.txt
  T: git git://repo.or.cz/qemu/ericb.git nbd

Reviewed-by: Eric Blake <address@hidden>

At this point, I think I'll touch up the issues I've spotted and submit a pull request, in order to make it easier for me to test my libvirt code.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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