From dbc7b01492371e4a54b92d2b6d968f9b863cc794 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Tue, 27 Oct 2020 00:05:55 -0500 Subject: 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 Message-Id: <20201027050556.269064-11-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- qapi/block-core.json | 7 +++++-- qapi/block-export.json | 7 ++++++- 2 files changed, 11 insertions(+), 3 deletions(-) (limited to 'qapi') diff --git a/qapi/block-core.json b/qapi/block-core.json index e00fc27..1b8b415 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -3905,9 +3905,12 @@ # # @tls-creds: TLS credentials ID # -# @x-dirty-bitmap: A "qemu:dirty-bitmap:NAME" string to query in place of +# @x-dirty-bitmap: A metadata context name such as "qemu:dirty-bitmap:NAME" +# or "qemu:allocation-depth" to query in place of the # traditional "base:allocation" block status (see -# NBD_OPT_LIST_META_CONTEXT in the NBD protocol) (since 3.0) +# NBD_OPT_LIST_META_CONTEXT in the NBD protocol; and +# yes, naming this option x-context would have made +# more sense) (since 3.0) # # @reconnect-delay: On an unexpected disconnect, the nbd client tries to # connect again until succeeding or encountering a serious diff --git a/qapi/block-export.json b/qapi/block-export.json index c4125f4..a9f488f 100644 --- a/qapi/block-export.json +++ b/qapi/block-export.json @@ -90,11 +90,16 @@ # the metadata context name "qemu:dirty-bitmap:BITMAP" to inspect # each bitmap. # +# @allocation-depth: Also export the allocation depth map for @device, so +# the NBD client can use NBD_OPT_SET_META_CONTEXT with +# the metadata context name "qemu:allocation-depth" to +# inspect allocation details. (since 5.2) +# # Since: 5.2 ## { 'struct': 'BlockExportOptionsNbd', 'base': 'BlockExportOptionsNbdBase', - 'data': { '*bitmaps': ['str'] } } + 'data': { '*bitmaps': ['str'], '*allocation-depth': 'bool' } } ## # @BlockExportOptionsVhostUserBlk: -- cgit v1.1