Re: [RFC PATCH 12/22] nbd/server: Simplify export shutdown

[Eric Blake]

On 8/13/20 11:29 AM, Kevin Wolf wrote:
> Closing export is somewhat convoluted because nbd_export_close() and
> nbd_export_put() call each other and the ways they actually end up being
> nested is not necessarily obvious.

You are in a maze of twisty little passages, all alike.

Yes, I've always hated that part of the code; thanks for tackling a cleanup.

> However, it is not really necessary to call nbd_export_close() from
> nbd_export_put() when putting the last reference because it only does
> three things:
>
> 1. Close all clients. We're going to refcount 0 and all clients hold a
>     reference, so we know there is no active client any more.
>
> 2. Close the user reference (represented by exp->name being non-NULL).
>     The same argument applies: If the export were still named, we would
>     still have a reference.
>
> 3. Freeing exp->description. This is really cleanup work to be done when
>     the export is finally freed. There is no reason to already clear it
>     while clients are still in the process of shutting down.
>
> So after moving the cleanup of exp->description, the code can be
> simplified so that only nbd_export_close() calls nbd_export_put(), but
> never the other way around.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   nbd/server.c | 17 ++++-------------
>   1 file changed, 4 insertions(+), 13 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

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Eric Blake, Principal Software Engineer
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