qemu/docs/tools
Eric Blake dbc7b01492 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>
2020-10-30 15:22:00 -05:00
..
conf.py docs: Move tools documentation to tools manual 2020-02-25 10:48:06 +00:00
index.rst docs: Move tools documentation to tools manual 2020-02-25 10:48:06 +00:00
qemu-img.rst qemu-img: add support for rate limit in qemu-img convert 2020-10-27 15:26:20 +01:00
qemu-nbd.rst nbd: Add 'qemu-nbd -A' to expose allocation depth 2020-10-30 15:22:00 -05:00
qemu-trace-stap.rst docs: Move tools documentation to tools manual 2020-02-25 10:48:06 +00:00
virtfs-proxy-helper.rst docs: Move tools documentation to tools manual 2020-02-25 10:48:06 +00:00
virtiofsd.rst tools/virtiofsd: xattr name mappings: Simple 'map' 2020-10-26 18:35:32 +00:00