Kevin Wolf writes:
> Add an option in BlockExportOptions to allow creating an export on an
> inactive node without activating the node. This mode needs to be
> explicitly supported by the export type (so that it doesn't perform any
> operations that are forbidden for inactive nodes), so this patch alone
> doesn't allow this option to be successfully used yet.
>
> Signed-off-by: Kevin Wolf
> ---
> qapi/block-export.json | 10 +-
> include/block/block-global-state.h | 3 +++
> include/block/export.h | 3 +++
> block.c| 4
> block/export/export.c | 31 --
> 5 files changed, 40 insertions(+), 11 deletions(-)
>
> diff --git a/qapi/block-export.json b/qapi/block-export.json
> index ce33fe378d..117b05d13c 100644
> --- a/qapi/block-export.json
> +++ b/qapi/block-export.json
> @@ -372,6 +372,13 @@
> # cannot be moved to the iothread. The default is false.
> # (since: 5.2)
> #
> +# @allow-inactive: If true, the export allows the exported node to be
> inactive.
> +# If it is created for an inactive block node, the node remains
> inactive. If
> +# the export type doesn't support running on an inactive node, an error
> is
> +# returned. If false, inactive block nodes are automatically activated
> before
> +# creating the export and trying to inactivate them later fails.
> +# (since: 10.0; default: false)
> +#
> # Since: 4.2
> ##
> { 'union': 'BlockExportOptions',
> @@ -381,7 +388,8 @@
> '*iothread': 'str',
> 'node-name': 'str',
> '*writable': 'bool',
> -'*writethrough': 'bool' },
> +'*writethrough': 'bool',
> +'*allow-inactive': 'bool' },
>'discriminator': 'type',
>'data': {
>'nbd': 'BlockExportOptionsNbd',
> diff --git a/include/block/block-global-state.h
> b/include/block/block-global-state.h
> index 22ec21117d..9be34b3c99 100644
> --- a/include/block/block-global-state.h
> +++ b/include/block/block-global-state.h
> @@ -175,6 +175,9 @@ BlockDriverState * GRAPH_RDLOCK
> check_to_replace_node(BlockDriverState *parent_bs, const char *node_name,
>Error **errp);
>
> +
> +bool GRAPH_RDLOCK bdrv_is_inactive(BlockDriverState *bs);
> +
> int no_coroutine_fn GRAPH_RDLOCK
> bdrv_activate(BlockDriverState *bs, Error **errp);
>
> diff --git a/include/block/export.h b/include/block/export.h
> index f2fe0f8078..4bd9531d4d 100644
> --- a/include/block/export.h
> +++ b/include/block/export.h
> @@ -29,6 +29,9 @@ typedef struct BlockExportDriver {
> */
> size_t instance_size;
>
> +/* True if the export type supports running on an inactive node */
> +bool supports_inactive;
> +
> /* Creates and starts a new block export */
> int (*create)(BlockExport *, BlockExportOptions *, Error **);
>
> diff --git a/block.c b/block.c
> index 61e131e71f..7eeb8d076e 100644
> --- a/block.c
> +++ b/block.c
> @@ -6845,6 +6845,10 @@ void bdrv_init_with_whitelist(void)
> bdrv_init();
> }
>
> +bool bdrv_is_inactive(BlockDriverState *bs) {
> +return bs->open_flags & BDRV_O_INACTIVE;
> +}
This function is needed by patch 1/15.
> +
> int bdrv_activate(BlockDriverState *bs, Error **errp)
> {
> BdrvChild *child, *parent;
> diff --git a/block/export/export.c b/block/export/export.c
> index bac42b8608..f3bbf11070 100644
> --- a/block/export/export.c
> +++ b/block/export/export.c
> @@ -75,6 +75,7 @@ static const BlockExportDriver
> *blk_exp_find_driver(BlockExportType type)
> BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
> {
> bool fixed_iothread = export->has_fixed_iothread &&
> export->fixed_iothread;
> +bool allow_inactive = export->has_allow_inactive &&
> export->allow_inactive;
> const BlockExportDriver *drv;
> BlockExport *exp = NULL;
> BlockDriverState *bs;
> @@ -138,17 +139,24 @@ BlockExport *blk_exp_add(BlockExportOptions *export,
> Error **errp)
> }
> }
>
> -/*
> - * Block exports are used for non-shared storage migration. Make sure
> - * that BDRV_O_INACTIVE is cleared and the image is ready for write
> - * access since the export could be available before migration handover.
> - * ctx was acquired in the caller.
> - */
> bdrv_graph_rdlock_main_loop();
> -ret = bdrv_activate(bs, errp);
> -if (ret < 0) {
> -bdrv_graph_rdunlock_main_loop();
> -goto fail;
> +if (allow_inactive) {
> +if (!drv->supports_inactive) {
> +error_setg(errp, "Export type does not support inactive
> exports");
> +bdrv_graph_rdunlock_main_loop();
> +goto fail;
> +}
> +} else {
> +/*
> + * Block exports are used for non-shared storage migration. Make sure
> + * that BDRV_O_INACTIVE is cleared and the image is ready for write
> + * access since the export
