block/export: Add BLOCK_EXPORT_DELETED event

Clients may want to know when an export has finally disappeard
(block-export-del returns earlier than that in the general case), so add
a QAPI event for it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200924152717.287415-22-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/export/export.c

@@ -19,6 +19,7 @@
 #include "block/nbd.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-block-export.h"
+#include "qapi/qapi-events-block-export.h"
 #include "qemu/id.h"
 
 static const BlockExportDriver *blk_exp_drivers[] = {
@@ -113,6 +114,7 @@ static void blk_exp_delete_bh(void *opaque)
     assert(exp->refcount == 0);
     QLIST_REMOVE(exp, next);
     exp->drv->delete(exp);
+    qapi_event_send_block_export_deleted(exp->id);
     g_free(exp->id);
     g_free(exp);
 

qapi/block-export.json

@@ -233,3 +233,15 @@
 ##
 { 'command': 'block-export-del',
   'data': { 'id': 'str', '*mode': 'BlockExportRemoveMode' } }
+
+##
+# @BLOCK_EXPORT_DELETED:
+#
+# Emitted when a block export is removed and its id can be reused.
+#
+# @id: Block export id.
+#
+# Since: 5.2
+##
+{ 'event': 'BLOCK_EXPORT_DELETED',
+  'data': { 'id': 'str' } }

tests/qemu-iotests/140

@@ -81,10 +81,17 @@ $QEMU_IO_PROG -f raw -r -c 'read -P 42 0 64k' \
     "nbd+unix:///drv?socket=$SOCK_DIR/nbd" 2>&1 \
     | _filter_qemu_io | _filter_nbd
 
+# The order of 'return' and the BLOCK_EXPORT_DELETED event is undefined. Just
+# wait until we've twice seen one of them. Filter the 'return' line out so that
+# the output is defined.
 _send_qemu_cmd $QEMU_HANDLE \
     "{ 'execute': 'eject',
        'arguments': { 'device': 'drv' }}" \
-    'return'
+    'return\|BLOCK_EXPORT_DELETED' |
+    grep -v 'return'
+
+_send_qemu_cmd $QEMU_HANDLE '' 'return\|BLOCK_EXPORT_DELETED' |
+    grep -v 'return'
 
 $QEMU_IO_PROG -f raw -r -c close \
     "nbd+unix:///drv?socket=$SOCK_DIR/nbd" 2>&1 \

tests/qemu-iotests/140.out

@@ -11,7 +11,7 @@ wrote 65536/65536 bytes at offset 0
 read 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 { 'execute': 'eject', 'arguments': { 'device': 'drv' }}
-{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "drv"}}
 qemu-io: can't open device nbd+unix:///drv?socket=SOCK_DIR/nbd: Requested export not available
 server reported: export 'drv' not present
 { 'execute': 'quit' }

tests/qemu-iotests/223.out

@@ -102,8 +102,10 @@ read 2097152/2097152 bytes at offset 2097152
 {"execute":"nbd-server-remove", "arguments":{"name":"n"}}
 {"return": {}}
 {"execute":"nbd-server-remove", "arguments":{"name":"n2"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n"}}
 {"return": {}}
 {"execute":"nbd-server-remove", "arguments":{"name":"n2"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n2"}}
 {"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
 {"execute":"nbd-server-stop"}
 {"return": {}}
@@ -183,8 +185,10 @@ read 2097152/2097152 bytes at offset 2097152
 {"execute":"nbd-server-remove", "arguments":{"name":"n"}}
 {"return": {}}
 {"execute":"nbd-server-remove", "arguments":{"name":"n2"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n"}}
 {"return": {}}
 {"execute":"nbd-server-remove", "arguments":{"name":"n2"}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n2"}}
 {"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
 {"execute":"nbd-server-stop"}
 {"return": {}}