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Re: [PATCH v2 18/19] qapi: backup: add immutable-source parameter
From: |
Markus Armbruster |
Subject: |
Re: [PATCH v2 18/19] qapi: backup: add immutable-source parameter |
Date: |
Wed, 01 Sep 2021 13:47:54 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:
> We are on the way to implement internal-backup with fleecing scheme,
> which includes backup job copying from fleecing block driver node
> (which is target of copy-before-write filter) to final target of
> backup. This job doesn't need own filter, as fleecing block driver node
> is a kind of snapshot, it's immutable from reader point of view.
>
> Let's add a parameter for backup to not insert filter but instead
> unshare writes on source. This way backup job becomes a simple copying
> process.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> qapi/block-core.json | 12 +++++++-
> include/block/block_int.h | 1 +
> block/backup.c | 61 +++++++++++++++++++++++++++++++++++----
> block/replication.c | 2 +-
> blockdev.c | 1 +
> 5 files changed, 70 insertions(+), 7 deletions(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 8a333136f5..995ca16a5e 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1391,6 +1391,15 @@
> # above node specified by @drive. If this option is not
> given,
> # a node name is autogenerated. (Since: 4.2)
> #
> +# @immutable-source: If true, assume source is immutable and don't insert
> filter
Suggest comma after immutable.
> +# as no copy-before-write operations are needed. It will
> +# fail if there are existing writers on source node, as
> well,
> +# any attempt to add writer to source node during backup
> will
> +# fail. @filter-node-name must not be set.
Suggest to split the sentence like "... fail if there are existing
writers on source node. Any attempt ... will also fail."
> +# If false, insert copy-before-write filter above source
> node
> +# (see also @filter-node-name parameter).
> +# Default is false. (Since 6.2)
> +#
> # @x-perf: Performance options. (Since 6.0)
> #
> # Note: @on-source-error and @on-target-error only affect background
> @@ -1407,7 +1416,8 @@
> '*on-source-error': 'BlockdevOnError',
> '*on-target-error': 'BlockdevOnError',
> '*auto-finalize': 'bool', '*auto-dismiss': 'bool',
> - '*filter-node-name': 'str', '*x-perf': 'BackupPerf' } }
> + '*filter-node-name': 'str', '*immutable-source': 'bool',
> + '*x-perf': 'BackupPerf' } }
>
> ##
> # @DriveBackup:
[...]
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