Commit 3229a835 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Eric Blake
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docs/interop: add nbd.txt 



Describe new metadata namespace: "qemu".

Signed-off-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20180609151758.17343-7-vsementsov@virtuozzo.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
[eblake: grammar tweaks]
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
parent 767f0c7d

MAINTAINERS

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@@ -1972,6 +1972,7 @@ 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



NFS

docs/interop/nbd.txt

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Qemu supports the NBD protocol, and has an internal NBD client (see

block/nbd.c), an internal NBD server (see blockdev-nbd.c), and an

external NBD server tool (see qemu-nbd.c). The common code is placed

in nbd/*.



The NBD protocol is specified here:

https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md



The following paragraphs describe some specific properties of NBD

protocol realization in Qemu.



= Metadata namespaces =



Qemu supports the "base:allocation" metadata context as defined in the

NBD protocol specification, and also defines an additional metadata

namespace "qemu".





== "qemu" namespace ==



The "qemu" namespace currently contains only one type of context,

related to exposing the contents of a dirty bitmap alongside the

associated disk contents.  That context has the following form:



    qemu:dirty-bitmap:<dirty-bitmap-export-name>



Each dirty-bitmap metadata context defines 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

in addition to "qemu:dirty-bitmap:<dirty-bitmap-export-name>":



* "qemu:" - returns list of all available metadata contexts in the

            namespace.

* "qemu:dirty-bitmap:" - returns list of all available dirty-bitmap

                         metadata contexts.