Dump: add qmp command "query-dump"

When dump-guest-memory is requested with detach flag, after its
return, user could query its status using "query-dump" command (with
no argument). The result contains:

- status: current dump status
- completed: bytes written in the latest dump
- total: bytes to write in the latest dump

From completed and total, we could know how much work
finished by calculating:

  100.0 * completed / total (%)

Reviewed-by:   Fam Zheng <famz@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <1455772616-8668-10-git-send-email-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 76 insertions, 6 deletions

diff --git a/dump.c b/dump.c
index cd4ae5e9e6..9dc494619d 100644
--- a/dump.c
+++ b/dump.c
@@ -1456,7 +1456,7 @@ static void dump_state_prepare(DumpState *s)
 bool dump_in_progress(void)
 {
     DumpState *state = &dump_state_global;
-    return (state->status == DUMP_STATUS_ACTIVE);
+    return (atomic_read(&state->status) == DUMP_STATUS_ACTIVE);
 }
 
 /* calculate total size of memory to be dumped (taking filter into
@@ -1669,9 +1669,12 @@ static void dump_process(DumpState *s, Error **errp)
         create_vmcore(s, &local_err);
     }
 
-    s->status = (local_err ? DUMP_STATUS_FAILED : DUMP_STATUS_COMPLETED);
-    error_propagate(errp, local_err);
+    /* make sure status is written after written_size updates */
+    smp_wmb();
+    atomic_set(&s->status,
+               (local_err ? DUMP_STATUS_FAILED : DUMP_STATUS_COMPLETED));
 
+    error_propagate(errp, local_err);
     dump_cleanup(s);
 }
 
@@ -1689,6 +1692,18 @@ static void *dump_thread(void *data)
     return NULL;
 }
 
+DumpQueryResult *qmp_query_dump(Error **errp)
+{
+    DumpQueryResult *result = g_new(DumpQueryResult, 1);
+    DumpState *state = &dump_state_global;
+    result->status = atomic_read(&state->status);
+    /* make sure we are reading status and written_size in order */
+    smp_rmb();
+    result->completed = state->written_size;
+    result->total = state->total_size;
+    return result;
+}
+
 void qmp_dump_guest_memory(bool paging, const char *file,
                            bool has_detach, bool detach,
                            bool has_begin, int64_t begin, bool has_length,
@@ -1779,7 +1794,7 @@ void qmp_dump_guest_memory(bool paging, const char *file,
               begin, length, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
-        s->status = DUMP_STATUS_FAILED;
+        atomic_set(&s->status, DUMP_STATUS_FAILED);
         return;
     }
 
diff --git a/qapi-schema.json b/qapi-schema.json
index ccd30c8a99..7b8f2a13e6 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2196,7 +2196,8 @@
 #               is the fd's name.
 #
 # @detach: #optional if true, QMP will return immediately rather than
-#          waiting for the dump to finish. (since 2.6).
+#          waiting for the dump to finish. The user can track progress
+#          using "query-dump". (since 2.6).
 #
 # @begin: #optional if specified, the starting physical address.
 #
@@ -2237,6 +2238,35 @@
   'data': [ 'none', 'active', 'completed', 'failed' ] }
 
 ##
+# @DumpQueryResult
+#
+# The result format for 'query-dump'.
+#
+# @status: enum of @DumpStatus, which shows current dump status
+#
+# @completed: bytes written in latest dump (uncompressed)
+#
+# @total: total bytes to be written in latest dump (uncompressed)
+#
+# Since 2.6
+##
+{ 'struct': 'DumpQueryResult',
+  'data': { 'status': 'DumpStatus',
+            'completed': 'int',
+            'total': 'int' } }
+
+##
+# @query-dump
+#
+# Query latest dump status.
+#
+# Returns: A @DumpStatus object showing the dump status.
+#
+# Since: 2.6
+##
+{ 'command': 'query-dump', 'returns': 'DumpQueryResult' }
+
+##
 # @DumpGuestMemoryCapability:
 #
 # A list of the available formats for dump-guest-memory
diff --git a/qmp-commands.hx b/qmp-commands.hx
index d30b1eb9b5..daaafe5aef 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -856,7 +856,8 @@ Arguments:
 - "protocol": destination file(started with "file:") or destination file
               descriptor (started with "fd:") (json-string)
 - "detach": if specified, command will return immediately, without waiting
-            for the dump to finish (json-bool)
+            for the dump to finish. The user can track progress using
+            "query-dump". (json-bool)
 - "begin": the starting physical address. It's optional, and should be specified
            with length together (json-int)
 - "length": the memory size, in bytes. It's optional, and should be specified
@@ -896,6 +897,30 @@ Example:
 
 EQMP
 
+    {
+        .name       = "query-dump",
+        .args_type  = "",
+        .params     = "",
+        .help       = "query background dump status",
+        .mhandler.cmd_new = qmp_marshal_query_dump,
+    },
+
+SQMP
+query-dump
+----------
+
+Query background dump status.
+
+Arguments: None.
+
+Example:
+
+-> { "execute": "query-dump" }
+<- { "return": { "status": "active", "completed": 1024000,
+                 "total": 2048000 } }
+
+EQMP
+
 #if defined TARGET_S390X
     {
         .name       = "dump-skeys",