diff options
| author | Eric Blake <eblake@redhat.com> | 2020-10-27 00:05:55 -0500 |
|---|---|---|
| committer | Eric Blake <eblake@redhat.com> | 2020-10-30 15:22:00 -0500 |
| commit | dbc7b01492371e4a54b92d2b6d968f9b863cc794 (patch) | |
| tree | 24812091f95b86d03192a23bec70e21d9a5b74eb /docs/tools | |
| parent | 71719cd57fc02ddfd91a4a3ca3f469bfb4d221bc (diff) | |
nbd: Add 'qemu-nbd -A' to expose allocation depth
Allow the server to expose an additional metacontext to be requested
by savvy clients. qemu-nbd adds a new option -A to expose the
qemu:allocation-depth metacontext through NBD_CMD_BLOCK_STATUS; this
can also be set via QMP when using block-export-add.
qemu as client is hacked into viewing the key aspects of this new
context by abusing the already-experimental x-dirty-bitmap option to
collapse all depths greater than 2, which results in a tri-state value
visible in the output of 'qemu-img map --output=json' (yes, that means
x-dirty-bitmap is now a bit of a misnomer, but I didn't feel like
renaming it as it would introduce a needless break of back-compat,
even though we make no compat guarantees with x- members):
unallocated (depth 0) => "zero":false, "data":true
local (depth 1) => "zero":false, "data":false
backing (depth 2+) => "zero":true, "data":true
libnbd as client is probably a nicer way to get at the information
without having to decipher such hacks in qemu as client. ;)
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201027050556.269064-11-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Diffstat (limited to 'docs/tools')
| -rw-r--r-- | docs/tools/qemu-nbd.rst | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/docs/tools/qemu-nbd.rst b/docs/tools/qemu-nbd.rst index 667861cb22..fe41336dc5 100644 --- a/docs/tools/qemu-nbd.rst +++ b/docs/tools/qemu-nbd.rst @@ -72,10 +72,16 @@ driver options if ``--image-opts`` is specified. Export the disk as read-only. +.. option:: -A, --allocation-depth + + Expose allocation depth information via the + ``qemu:allocation-depth`` metadata context accessible through + NBD_OPT_SET_META_CONTEXT. + .. option:: -B, --bitmap=NAME If *filename* has a qcow2 persistent bitmap *NAME*, expose - that bitmap via the ``qemu:dirty-bitmap:NAME`` context + that bitmap via the ``qemu:dirty-bitmap:NAME`` metadata context accessible through NBD_OPT_SET_META_CONTEXT. .. option:: -s, --snapshot |