On 30.11.2015 16:36, Kevin Wolf wrote:
> Am 09.11.2015 um 23:39 hat Max Reitz geschrieben:
>> The NBD code uses the BDS close notifier to determine when a medium is
>> ejected. However, now it should use the BB's BDS removal notifier for
>> that instead of the BDS's close notifier.
>>
>> Signed-off-by: Max Reitz <mre...@redhat.com>
>> ---
>> blockdev-nbd.c | 37 +------------------------------------
>> nbd.c | 13 +++++++++++++
>> 2 files changed, 14 insertions(+), 36 deletions(-)
>>
>> diff --git a/blockdev-nbd.c b/blockdev-nbd.c
>> index bcdd18b..b28a55b 100644
>> --- a/blockdev-nbd.c
>> +++ b/blockdev-nbd.c
>> @@ -46,37 +46,11 @@ void qmp_nbd_server_start(SocketAddress *addr, Error
>> **errp)
>> }
>> }
>>
>> -/*
>> - * Hook into the BlockBackend notifiers to close the export when the
>> - * backend is closed.
>> - */
>> -typedef struct NBDCloseNotifier {
>> - Notifier n;
>> - NBDExport *exp;
>> - QTAILQ_ENTRY(NBDCloseNotifier) next;
>> -} NBDCloseNotifier;
>> -
>> -static QTAILQ_HEAD(, NBDCloseNotifier) close_notifiers =
>> - QTAILQ_HEAD_INITIALIZER(close_notifiers);
>> -
>> -static void nbd_close_notifier(Notifier *n, void *data)
>> -{
>> - NBDCloseNotifier *cn = DO_UPCAST(NBDCloseNotifier, n, n);
>> -
>> - notifier_remove(&cn->n);
>> - QTAILQ_REMOVE(&close_notifiers, cn, next);
>> -
>> - nbd_export_close(cn->exp);
>> - nbd_export_put(cn->exp);
>
> Here you remove a close/put pair, but in the new code you only add the
> close call. Why is this correct?Thanks for putting so much unfounded faith in me. :-) After having put quite some time into looking into it, first I have to say that it's a very good question. First off, it's wrong. This is because I thought every export would have a refcount of one. Turns out this is wrong, they have a refcount of two: It is created with a refcount of one, and then it gains another by giving it a name and entering it into the export list. I did know about the second but I completely forgot about the former. And indeed I do think it is wrong. qmp_nbd_server_add() does not keep the reference to the export, once the function returns, it is gone. Therefore, it should call nbd_export_put() before returning. So in my opinion the current code is wrong and I didn't fix it enough. *cough* So, with the nbd_export_put() added to qmp_nbd_server_add(), every export will have a refcount of 1 + |clients|. The eject notifier will call nbd_close_notifier(), which first disconnects the clients, thus reducing the refcount by |clients|, and then sets the name to NULL, thus dropping the final refcount and destroying the export. In the old code, we needed another nbd_export_put() because of the superfluous reference from nbd_export_new(), which doesn't actually exist for blockdev-nbd (it does for qemu-nbd, though). Max
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