[Qemu-devel] [PULL 3/8] qapi: add nbd-server-remove

[Eric Blake <eblake@redhat.com>]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Add command for removing an export. It is needed for cases when we
don't want to keep the export after the operation on it was completed.
The other example is a temporary node, created with blockdev-add.
If we want to delete it we should firstly remove any corresponding
NBD export.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20180119135719.24745-3-vsementsov@virtuozzo.com>
[eblake: drop dead nb_clients code]
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 qapi/block.json     | 41 +++++++++++++++++++++++++++++++++++++++++
 include/block/nbd.h |  1 +
 blockdev-nbd.c      | 24 ++++++++++++++++++++++++
 nbd/server.c        | 13 +++++++++++++
 4 files changed, 79 insertions(+)

diff --git a/qapi/block.json b/qapi/block.json
index 353e3a45bdf..c6945240029 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -227,6 +227,47 @@
 { 'command': 'nbd-server-add',
   'data': {'device': 'str', '*name': 'str', '*writable': 'bool'} }

+##
+# @NbdServerRemoveMode:
+#
+# Mode for removing an NBD export.
+#
+# @safe: Remove export if there are no existing connections, fail otherwise.
+#
+# @hard: Drop all connections immediately and remove export.
+#
+# Potential additional modes to be added in the future:
+#
+# hide: Just hide export from new clients, leave existing connections as is.
+#       Remove export after all clients are disconnected.
+#
+# soft: Hide export from new clients, answer with ESHUTDOWN for all further
+#       requests from existing clients.
+#
+# Since: 2.12
+##
+{'enum': 'NbdServerRemoveMode', 'data': ['safe', 'hard']}
+
+##
+# @nbd-server-remove:
+#
+# Remove NBD export by name.
+#
+# @name: Export name.
+#
+# @mode: Mode of command operation. See @NbdServerRemoveMode description.
+#        Default is 'safe'.
+#
+# Returns: error if
+#            - the server is not running
+#            - export is not found
+#            - mode is 'safe' and there are existing connections
+#
+# Since: 2.12
+##
+{ 'command': 'nbd-server-remove',
+  'data': {'name': 'str', '*mode': 'NbdServerRemoveMode'} }
+
 ##
 # @nbd-server-stop:
 #
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 978e4433664..ee74ec391a8 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -261,6 +261,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
                           bool writethrough, BlockBackend *on_eject_blk,
                           Error **errp);
 void nbd_export_close(NBDExport *exp);
+void nbd_export_remove(NBDExport *exp, NbdServerRemoveMode mode, Error **errp);
 void nbd_export_get(NBDExport *exp);
 void nbd_export_put(NBDExport *exp);

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 104789e521c..a9f79c6778e 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -189,6 +189,30 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
     nbd_export_put(exp);
 }

+void qmp_nbd_server_remove(const char *name,
+                           bool has_mode, NbdServerRemoveMode mode,
+                           Error **errp)
+{
+    NBDExport *exp;
+
+    if (!nbd_server) {
+        error_setg(errp, "NBD server not running");
+        return;
+    }
+
+    exp = nbd_export_find(name);
+    if (exp == NULL) {
+        error_setg(errp, "Export '%s' is not found", name);
+        return;
+    }
+
+    if (!has_mode) {
+        mode = NBD_SERVER_REMOVE_MODE_SAFE;
+    }
+
+    nbd_export_remove(exp, mode, errp);
+}
+
 void qmp_nbd_server_stop(Error **errp)
 {
     nbd_export_close_all();
diff --git a/nbd/server.c b/nbd/server.c
index 6caa8d17be7..112e3f69dff 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1177,6 +1177,19 @@ void nbd_export_close(NBDExport *exp)
     nbd_export_put(exp);
 }

+void nbd_export_remove(NBDExport *exp, NbdServerRemoveMode mode, Error **errp)
+{
+    if (mode == NBD_SERVER_REMOVE_MODE_HARD || QTAILQ_EMPTY(&exp->clients)) {
+        nbd_export_close(exp);
+        return;
+    }
+
+    assert(mode == NBD_SERVER_REMOVE_MODE_SAFE);
+
+    error_setg(errp, "export '%s' still in use", exp->name);
+    error_append_hint(errp, "Use mode='hard' to force client disconnect\n");
+}
+
 void nbd_export_get(NBDExport *exp)
 {
     assert(exp->refcount > 0);
-- 
2.14.3