mirror of
https://github.com/xemu-project/xemu.git
synced 2024-11-30 23:10:38 +00:00
5135fe7110
Replace Qemu -> QEMU. Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> Reviewed-by: Darren Kenny <darren.kenny@oracle.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20211118143401.4101497-1-philmd@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
71 lines
2.7 KiB
Plaintext
71 lines
2.7 KiB
Plaintext
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 two available metadata context
|
|
types. The first is related to exposing the contents of a dirty
|
|
bitmap alongside the associated disk contents. That metadata context
|
|
is named with 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, set when the extent is "dirty"
|
|
|
|
The second is related to exposing the source of various extents within
|
|
the image, with a single metadata context named:
|
|
|
|
qemu:allocation-depth
|
|
|
|
In the allocation depth context, the entire 32-bit value represents a
|
|
depth of which layer in a thin-provisioned backing chain provided the
|
|
data (0 for unallocated, 1 for the active layer, 2 for the first
|
|
backing layer, and so forth).
|
|
|
|
For NBD_OPT_LIST_META_CONTEXT the following queries are supported
|
|
in addition to the specific "qemu:allocation-depth" and
|
|
"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.
|
|
|
|
= Features by version =
|
|
|
|
The following list documents which qemu version first implemented
|
|
various features (both as a server exposing the feature, and as a
|
|
client taking advantage of the feature when present), to make it
|
|
easier to plan for cross-version interoperability. Note that in
|
|
several cases, the initial release containing a feature may require
|
|
additional patches from the corresponding stable branch to fix bugs in
|
|
the operation of that feature.
|
|
|
|
* 2.6: NBD_OPT_STARTTLS with TLS X.509 Certificates
|
|
* 2.8: NBD_CMD_WRITE_ZEROES
|
|
* 2.10: NBD_OPT_GO, NBD_INFO_BLOCK
|
|
* 2.11: NBD_OPT_STRUCTURED_REPLY
|
|
* 2.12: NBD_CMD_BLOCK_STATUS for "base:allocation"
|
|
* 3.0: NBD_OPT_STARTTLS with TLS Pre-Shared Keys (PSK),
|
|
NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE
|
|
* 4.2: NBD_FLAG_CAN_MULTI_CONN for shareable read-only exports,
|
|
NBD_CMD_FLAG_FAST_ZERO
|
|
* 5.2: NBD_CMD_BLOCK_STATUS for "qemu:allocation-depth"
|