From 3859ad36f0bdf45a6610d93296b52c9604b6d6f7 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 24 Sep 2020 17:27:05 +0200 Subject: [PATCH] block/export: Move strong user reference to block_exports 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 Reviewed-by: Max Reitz Message-Id: <20200924152717.287415-20-kwolf@redhat.com> Acked-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- block/export/export.c | 6 ++++++ blockdev-nbd.c | 5 ----- include/block/export.h | 8 ++++++++ nbd/server.c | 2 -- 4 files changed, 14 insertions(+), 7 deletions(-) diff --git a/block/export/export.c b/block/export/export.c index 7a4a78449a0..62699dfa050 100644 --- a/block/export/export.c +++ b/block/export/export.c @@ -80,6 +80,7 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp) *exp = (BlockExport) { .drv = drv, .refcount = 1, + .user_owned = true, .id = g_strdup(export->id), }; @@ -143,6 +144,11 @@ void blk_exp_request_shutdown(BlockExport *exp) aio_context_acquire(aio_context); exp->drv->request_shutdown(exp); + + assert(exp->user_owned); + exp->user_owned = false; + blk_exp_unref(exp); + aio_context_release(aio_context); } diff --git a/blockdev-nbd.c b/blockdev-nbd.c index 814554dd90e..9efbaef8f76 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -235,11 +235,6 @@ int nbd_export_create(BlockExport *exp, BlockExportOptions *exp_args, goto out; } - /* The list of named exports has a strong reference to this export now and - * our only way of accessing it is through nbd_export_find(), so we can drop - * the strong reference that is @exp. */ - blk_exp_unref(exp); - ret = 0; out: aio_context_release(aio_context); diff --git a/include/block/export.h b/include/block/export.h index cdc6e161ead..4833947e89c 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). + */ + bool user_owned; + /* The AioContext whose lock protects this BlockExport object. */ AioContext *ctx; diff --git a/nbd/server.c b/nbd/server.c index 32147e4871a..22a1d66168f 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1616,7 +1616,6 @@ int nbd_export_new(BlockExport *blk_exp, BlockDriverState *bs, blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp); - blk_exp_ref(&exp->common); QTAILQ_INSERT_TAIL(&exports, exp, next); return 0; @@ -1663,7 +1662,6 @@ static void nbd_export_request_shutdown(BlockExport *blk_exp) client_close(client, true); } if (exp->name) { - blk_exp_unref(&exp->common); g_free(exp->name); exp->name = NULL; QTAILQ_REMOVE(&exports, exp, next); -- 2.39.5