| Message ID | 20200813162935.210070-13-kwolf@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | block/export: Add infrastructure and QAPI for block exports | expand |
On 13.08.20 18:29, 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. > > 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. Convincing. > 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: Max Reitz <mreitz@redhat.com>
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>
diff --git a/nbd/server.c b/nbd/server.c index eadc5b9804..4c594e6558 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1678,8 +1678,6 @@ void nbd_export_close(NBDExport *exp) QTAILQ_REMOVE(&exports, exp, next); QTAILQ_INSERT_TAIL(&closed_exports, exp, next); } - g_free(exp->description); - exp->description = NULL; nbd_export_put(exp); } @@ -1706,19 +1704,12 @@ void nbd_export_get(NBDExport *exp) void nbd_export_put(NBDExport *exp) { assert(exp->refcount > 0); - if (exp->refcount == 1) { - nbd_export_close(exp); - } - - /* nbd_export_close() may theoretically reduce refcount to 0. It may happen - * if someone calls nbd_export_put() on named export not through - * nbd_export_set_name() when refcount is 1. So, let's assert that - * it is > 0. - */ - assert(exp->refcount > 0); if (--exp->refcount == 0) { assert(exp->name == NULL); - assert(exp->description == NULL); + assert(QTAILQ_EMPTY(&exp->clients)); + + g_free(exp->description); + exp->description = NULL; if (exp->blk) { if (exp->eject_notifier_blk) {
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. 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(-)