[Qemu-devel] [PATCH v5 10/11] Dump: add qmp command "query-dump"

[Peter Xu <peterx@redhat.com>]

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 (%)

Also, enrich DUMP_COMPLETED event to contain dump results when
finished.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 docs/qmp-events.txt |  5 ++++-
 dump.c              | 28 ++++++++++++++++++++++++----
 qapi-schema.json    | 34 ++++++++++++++++++++++++++++++++--
 qapi/event.json     |  4 +++-
 qmp-commands.hx     | 29 +++++++++++++++++++++++++++--
 5 files changed, 90 insertions(+), 10 deletions(-)

diff --git a/docs/qmp-events.txt b/docs/qmp-events.txt
index 1f79588..60af2ab 100644
--- a/docs/qmp-events.txt
+++ b/docs/qmp-events.txt
@@ -227,6 +227,8 @@ Emitted when the guest has finished one memory dump.
 
 Data:
 
+- "result": DumpQueryResult type as described in qapi-schema.json
+
 - "error": Error message when dump failed. This is only a
   human-readable string provided when dump failed. It should not be
   parsed in any way (json-string, optional)
@@ -234,7 +236,8 @@ Data:
 Example:
 
 { "event": "DUMP_COMPLETED",
-  "data": {} }
+  "data": {"result": {"total": 1090650112, "status": "completed",
+                      "completed": 1090650112} } }
 
 GUEST_PANICKED
 --------------
diff --git a/dump.c b/dump.c
index ff543ae..c566a32 100644
--- a/dump.c
+++ b/dump.c
@@ -1433,7 +1433,7 @@ 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
@@ -1634,6 +1634,7 @@ cleanup:
 static void dump_process(DumpState *s, Error **errp)
 {
     Error *local_err = NULL;
+    DumpQueryResult *result = NULL;
 
     if (s->has_format && s->format != DUMP_GUEST_MEMORY_FORMAT_ELF) {
         create_kdump_vmcore(s, &local_err);
@@ -1641,12 +1642,19 @@ static void dump_process(DumpState *s, Error **errp)
         create_vmcore(s, &local_err);
     }
 
-    s->status = (local_err ? DUMP_STATUS_FAILED : DUMP_STATUS_COMPLETED);
+    /* make sure status is written after written_size updates */
+    smp_wmb();
+    atomic_set(&s->status,
+               (local_err ? DUMP_STATUS_FAILED : DUMP_STATUS_COMPLETED));
 
     /* send DUMP_COMPLETED message (unconditionally) */
-    qapi_event_send_dump_completed(!!local_err, (local_err ? \
+    result = qmp_query_dump(NULL);
+    /* should never fails */
+    assert(result);
+    qapi_event_send_dump_completed(result, !!local_err, (local_err ? \
                                    error_get_pretty(local_err) : NULL),
                                    &error_abort);
+    qapi_free_DumpQueryResult(result);
 
     error_propagate(errp, local_err);
     dump_cleanup(s);
@@ -1661,6 +1669,18 @@ 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,
@@ -1751,7 +1771,7 @@ 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 f0d3c4a..71f6523 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2116,8 +2116,9 @@
 #               is the fd's name.
 #
 # @detach: #optional if true, QMP will return immediately rather than
-#          waiting for the dump to finish. A DUMP_COMPLETED event will
-#          occur at the end. (since 2.6).
+#          waiting for the dump to finish. The user can track progress
+#          using "query-dump". A DUMP_COMPLETED event will occur
+#          at the end. (since 2.6).
 #
 # @begin: #optional if specified, the starting physical address.
 #
@@ -2158,6 +2159,35 @@
   '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/qapi/event.json b/qapi/event.json
index b18ed66..bf7dd61 100644
--- a/qapi/event.json
+++ b/qapi/event.json
@@ -362,6 +362,8 @@
 #
 # Emitted when background dump has completed
 #
+# @result: DumpQueryResult type described in qapi-schema.json.
+#
 # @error: #optional human-readable error string that provides
 #         hint on why dump failed. Only presents on failure. The
 #         user should not try to interpret the error string.
@@ -369,4 +371,4 @@
 # Since: 2.6
 ##
 { 'event': 'DUMP_COMPLETED' ,
-  'data': { '*error': 'str' } }
+  'data': { 'result': 'DumpQueryResult', '*error': 'str' } }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 7b6f915..eb5bfe2 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -858,8 +858,9 @@ Arguments:
 - "protocol": destination file(started with "file:") or destination file
               descriptor (started with "fd:") (json-string)
 - "detach": if specified, command will return immediately rather than waiting
-            for the dump completion. A DUMP_COMPLETED event will occur at
-            the end. (json-bool)
+            for the dump completion. The user can track progress using
+            "query-dump" A DUMP_COMPLETED event will occur at the
+            end. (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
@@ -899,6 +900,30 @@ 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",
-- 
2.4.3