block/export: Add block-export-del

Implement a new QMP command block-export-del and make nbd-server-remove
a wrapper around it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-21-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 44 insertions, 3 deletions

diff --git a/block/export/export.c b/block/export/export.c
index 62699dfa05..d186beffe9 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -29,7 +29,7 @@ static const BlockExportDriver *blk_exp_drivers[] = {
 static QLIST_HEAD(, BlockExport) block_exports =
     QLIST_HEAD_INITIALIZER(block_exports);
 
-static BlockExport *blk_exp_find(const char *id)
+BlockExport *blk_exp_find(const char *id)
 {
     BlockExport *exp;
 
@@ -143,12 +143,23 @@ void blk_exp_request_shutdown(BlockExport *exp)
     AioContext *aio_context = exp->ctx;
 
     aio_context_acquire(aio_context);
+
+    /*
+     * If the user doesn't own the export any more, it is already shutting
+     * down. We must not call .request_shutdown and decrease the refcount a
+     * second time.
+     */
+    if (!exp->user_owned) {
+        goto out;
+    }
+
     exp->drv->request_shutdown(exp);
 
     assert(exp->user_owned);
     exp->user_owned = false;
     blk_exp_unref(exp);
 
+out:
     aio_context_release(aio_context);
 }
 
@@ -199,3 +210,33 @@ void qmp_block_export_add(BlockExportOptions *export, Error **errp)
 {
     blk_exp_add(export, errp);
 }
+
+void qmp_block_export_del(const char *id,
+                          bool has_mode, BlockExportRemoveMode mode,
+                          Error **errp)
+{
+    ERRP_GUARD();
+    BlockExport *exp;
+
+    exp = blk_exp_find(id);
+    if (exp == NULL) {
+        error_setg(errp, "Export '%s' is not found", id);
+        return;
+    }
+    if (!exp->user_owned) {
+        error_setg(errp, "Export '%s' is already shutting down", id);
+        return;
+    }
+
+    if (!has_mode) {
+        mode = BLOCK_EXPORT_REMOVE_MODE_SAFE;
+    }
+    if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE && exp->refcount > 1) {
+        error_setg(errp, "export '%s' still in use", exp->id);
+        error_append_hint(errp, "Use mode='hard' to force client "
+                          "disconnect\n");
+        return;
+    }
+
+    blk_exp_request_shutdown(exp);
+}
diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index db357cafcb..d15a2be827 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -476,8 +476,8 @@ void hmp_nbd_server_remove(Monitor *mon, const QDict *qdict)
     bool force = qdict_get_try_bool(qdict, "force", false);
     Error *err = NULL;
 
-    /* Rely on NBD_SERVER_REMOVE_MODE_SAFE being the default */
-    qmp_nbd_server_remove(name, force, NBD_SERVER_REMOVE_MODE_HARD, &err);
+    /* Rely on BLOCK_EXPORT_REMOVE_MODE_SAFE being the default */
+    qmp_nbd_server_remove(name, force, BLOCK_EXPORT_REMOVE_MODE_HARD, &err);
     hmp_handle_error(mon, err);
 }