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Diffstat (limited to 'docs/interop')
| -rw-r--r-- | docs/interop/nbd.txt | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt new file mode 100644 index 0000000000..77b5f45911 --- /dev/null +++ b/docs/interop/nbd.txt @@ -0,0 +1,38 @@ +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. |