Re: [PATCH 19/29] block/export: Move strong user reference to block_exports

[Max Reitz]

On 07.09.20 20:20, Kevin Wolf wrote:
> The reference owned by the user/monitor that is created when adding the
> export and dropped when removing it was tied to the 'exports' list in
> nbd/server.c. Every block export will have a user reference, so move it
> to the block export level and tie it to the 'block_exports' list in
> block/export/export.c instead. This is necessary for introducing a QMP
> command for removing exports.
> 
> Note that exports are present in block_exports even after the user has
> requested shutdown. This is different from NBD's exports where exports
> are immediately removed on a shutdown request, even if they are still in
> the process of shutting down. In order to avoid that the user still
> interacts with an export that is shutting down (and possibly removes it
> a second time), we need to remember if the user actually still owns it.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/export.h | 8 ++++++++
>  block/export/export.c  | 6 ++++++
>  blockdev-nbd.c         | 5 -----
>  nbd/server.c           | 2 --
>  4 files changed, 14 insertions(+), 7 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>

> diff --git a/include/block/export.h b/include/block/export.h
> index cdc6e161ea..4833947e89 100644
> --- a/include/block/export.h
> +++ b/include/block/export.h
> @@ -60,6 +60,14 @@ struct BlockExport {
>       */
>      int refcount;
>  
> +    /*
> +     * True if one of the references in refcount belongs to the user. After 
> the
> +     * user has dropped their reference, they may not e.g. remove the same
> +     * export a second time (which would decrease the refcount without having
> +     * it incremented first).

Not sure though whether this (or the request_shutdown documentation)
should mention that request_shutdown drops the user reference.

Max

> +     */
> +    bool user_owned;
> +

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