Re: [PATCH v4 27/34] migration: Add direct-io parameter

[Markus Armbruster <armbru@redhat.com>]

Fabiano Rosas <farosas@suse.de> writes:

> Add the direct-io migration parameter that tells the migration code to
> use O_DIRECT when opening the migration stream file whenever possible.
>
> This is currently only used with the fixed-ram migration that has a
> clear window guaranteed to perform aligned writes.
>
> Signed-off-by: Fabiano Rosas <farosas@suse.de>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index 3fce5fe53e..41241a2178 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -878,6 +878,9 @@
>  # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
>  #        (Since 8.2)
>  #
> +# @direct-io: Open migration files with O_DIRECT when possible. This
> +#     requires that the 'fixed-ram' capability is enabled. (since 9.0)

'fixed-ram' is a cross-reference to MigrationCapability member
fixed-ram.

For local members, @name is better than 'name', because @name carries
meaning, while 'name' could be anything.

Currently, @name is merely shorthand for ``name``, which is an reST
"inline literal", commonly used for short code snippets.  Rendered in
fixed-width font, unlike 'name'.

Making @name generating a link to the description would be a nice
improvement.

For non-local members, we can't make @name a link without also
specifying the thing it's a member of.

Let's stick to @name for member names, even non-local ones, so we get
the same font for all of them.

> +#
>  # Features:
>  #
>  # @deprecated: Member @block-incremental is deprecated.  Use
> @@ -911,7 +914,8 @@
>             'block-bitmap-mapping',
>             { 'name': 'x-vcpu-dirty-limit-period', 'features': ['unstable'] },
>             'vcpu-dirty-limit',
> -           'mode'] }
> +           'mode',
> +           'direct-io'] }
>  
>  ##
>  # @MigrateSetParameters:
> @@ -1070,6 +1074,9 @@
>  # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
>  #        (Since 8.2)
>  #
> +# @direct-io: Open migration files with O_DIRECT when possible. This
> +#     requires that the 'fixed-ram' capability is enabled. (since 9.0)
> +#
>  # Features:
>  #
>  # @deprecated: Member @block-incremental is deprecated.  Use
> @@ -1123,7 +1130,8 @@
>              '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
>                                              'features': [ 'unstable' ] },
>              '*vcpu-dirty-limit': 'uint64',
> -            '*mode': 'MigMode'} }
> +            '*mode': 'MigMode',
> +            '*direct-io': 'bool' } }
>  
>  ##
>  # @migrate-set-parameters:
> @@ -1298,6 +1306,9 @@
>  # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
>  #        (Since 8.2)
>  #
> +# @direct-io: Open migration files with O_DIRECT when possible. This
> +#     requires that the 'fixed-ram' capability is enabled. (since 9.0)
> +#
>  # Features:
>  #
>  # @deprecated: Member @block-incremental is deprecated.  Use
> @@ -1348,7 +1359,8 @@
>              '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
>                                              'features': [ 'unstable' ] },
>              '*vcpu-dirty-limit': 'uint64',
> -            '*mode': 'MigMode'} }
> +            '*mode': 'MigMode',
> +            '*direct-io': 'bool' } }
>  
>  ##
>  # @query-migrate-parameters:

Other than that, QAPI schema
Acked-by: Markus Armbruster <armbru@redhat.com>