[Qemu-devel] [PATCH v11 08/25] migration: introduce icount field for snapshots

[Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>]

Saving icount as a parameters of the snapshot allows navigation between
them in the execution replay scenario.
This information can be used for finding a specific snapshot for proceeding
the recorded execution to the specific moment of the time.
E.g., 'reverse step' action (introduced in one of the following patches)
needs to load the nearest snapshot which is prior to the current moment
of time .

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Acked-by: Markus Armbruster <armbru@redhat.com>

--

v2:
 - made icount in SnapshotInfo optional (suggested by Eric Blake)
v7:
 - added more comments for icount member (suggested by Markus Armbruster)
v9:
 - updated icount comment
v10:
 - updated icount comment again
---
 block/qapi.c             |   18 ++++++++++++++----
 block/qcow2-snapshot.c   |    2 ++
 blockdev.c               |   10 ++++++++++
 include/block/snapshot.h |    1 +
 migration/savevm.c       |    5 +++++
 qapi/block-core.json     |    7 ++++++-
 qapi/block.json          |    3 ++-
 7 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/block/qapi.c b/block/qapi.c
index c66f949..ccf23f3 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -210,6 +210,8 @@ int bdrv_query_snapshot_info_list(BlockDriverState *bs,
         info->date_nsec     = sn_tab[i].date_nsec;
         info->vm_clock_sec  = sn_tab[i].vm_clock_nsec / 1000000000;
         info->vm_clock_nsec = sn_tab[i].vm_clock_nsec % 1000000000;
+        info->icount        = sn_tab[i].icount;
+        info->has_icount    = sn_tab[i].icount != -1ULL;
 
         info_list = g_new0(SnapshotInfoList, 1);
         info_list->value = info;
@@ -663,14 +665,15 @@ void bdrv_snapshot_dump(fprintf_function func_fprintf, void *f,
                         QEMUSnapshotInfo *sn)
 {
     char buf1[128], date_buf[128], clock_buf[128];
+    char icount_buf[128] = {0};
     struct tm tm;
     time_t ti;
     int64_t secs;
 
     if (!sn) {
         func_fprintf(f,
-                     "%-10s%-20s%7s%20s%15s",
-                     "ID", "TAG", "VM SIZE", "DATE", "VM CLOCK");
+                     "%-10s%-18s%7s%20s%13s%11s",
+                     "ID", "TAG", "VM SIZE", "DATE", "VM CLOCK", "ICOUNT");
     } else {
         ti = sn->date_sec;
         localtime_r(&ti, &tm);
@@ -683,13 +686,18 @@ void bdrv_snapshot_dump(fprintf_function func_fprintf, void *f,
                  (int)((secs / 60) % 60),
                  (int)(secs % 60),
                  (int)((sn->vm_clock_nsec / 1000000) % 1000));
+        if (sn->icount != -1ULL) {
+            snprintf(icount_buf, sizeof(icount_buf),
+                "%"PRId64, sn->icount);
+        }
         func_fprintf(f,
-                     "%-10s%-20s%7s%20s%15s",
+                     "%-10s%-18s%7s%20s%13s%11s",
                      sn->id_str, sn->name,
                      get_human_readable_size(buf1, sizeof(buf1),
                                              sn->vm_state_size),
                      date_buf,
-                     clock_buf);
+                     clock_buf,
+                     icount_buf);
     }
 }
 
@@ -857,6 +865,8 @@ void bdrv_image_info_dump(fprintf_function func_fprintf, void *f,
                 .date_nsec = elem->value->date_nsec,
                 .vm_clock_nsec = elem->value->vm_clock_sec * 1000000000ULL +
                                  elem->value->vm_clock_nsec,
+                .icount = elem->value->has_icount ?
+                          elem->value->icount : -1ULL,
             };
 
             pstrcpy(sn.id_str, sizeof(sn.id_str), elem->value->id);
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index d682946..96b57f4 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -379,6 +379,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     sn->date_sec = sn_info->date_sec;
     sn->date_nsec = sn_info->date_nsec;
     sn->vm_clock_nsec = sn_info->vm_clock_nsec;
+    sn->icount = sn_info->icount;
 
     /* Allocate the L1 table of the snapshot and copy the current one there. */
     l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
@@ -698,6 +699,7 @@ int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
         sn_info->date_sec = sn->date_sec;
         sn_info->date_nsec = sn->date_nsec;
         sn_info->vm_clock_nsec = sn->vm_clock_nsec;
+        sn_info->icount = sn->icount;
     }
     *psn_tab = sn_tab;
     return s->nb_snapshots;
diff --git a/blockdev.c b/blockdev.c
index a8fa874..1f4499c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -57,6 +57,7 @@
 #include "block/trace.h"
 #include "sysemu/arch_init.h"
 #include "sysemu/qtest.h"
+#include "sysemu/replay.h"
 #include "qemu/cutils.h"
 #include "qemu/help_option.h"
 #include "qemu/throttle-options.h"
@@ -1239,6 +1240,10 @@ SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
     info->vm_state_size = sn.vm_state_size;
     info->vm_clock_nsec = sn.vm_clock_nsec % 1000000000;
     info->vm_clock_sec = sn.vm_clock_nsec / 1000000000;
+    if (sn.icount != -1ULL) {
+        info->icount = sn.icount;
+        info->has_icount = true;
+    }
 
     return info;
 
@@ -1447,6 +1452,11 @@ static void internal_snapshot_prepare(BlkActionState *common,
     sn->date_sec = tv.tv_sec;
     sn->date_nsec = tv.tv_usec * 1000;
     sn->vm_clock_nsec = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+    if (replay_mode != REPLAY_MODE_NONE) {
+        sn->icount = replay_get_current_step();
+    } else {
+        sn->icount = -1ULL;
+    }
 
     ret1 = bdrv_snapshot_create(bs, sn);
     if (ret1 < 0) {
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index f73d109..c9c8975 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -42,6 +42,7 @@ typedef struct QEMUSnapshotInfo {
     uint32_t date_sec; /* UTC date of the snapshot */
     uint32_t date_nsec;
     uint64_t vm_clock_nsec; /* VM clock relative to boot */
+    uint64_t icount; /* record/replay step */
 } QEMUSnapshotInfo;
 
 int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
diff --git a/migration/savevm.c b/migration/savevm.c
index 3226604..fa3b9d1 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2510,6 +2510,11 @@ int save_snapshot(const char *name, Error **errp)
     sn->date_sec = tv.tv_sec;
     sn->date_nsec = tv.tv_usec * 1000;
     sn->vm_clock_nsec = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+    if (replay_mode != REPLAY_MODE_NONE) {
+        sn->icount = replay_get_current_step();
+    } else {
+        sn->icount = -1ULL;
+    }
 
     if (name) {
         ret = bdrv_snapshot_find(bs, old_sn, name);
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 91685be..6d45c29 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -26,13 +26,18 @@
 #
 # @vm-clock-nsec: fractional part in nano seconds to be used with vm-clock-sec
 #
+# @icount: Current instruction count. Appears when execution record/replay
+#          is enabled. Used for "time-traveling" to match the moment
+#          in the recorded execution with the snapshots. (since 4.0)
+#
 # Since: 1.3
 #
 ##
 { 'struct': 'SnapshotInfo',
   'data': { 'id': 'str', 'name': 'str', 'vm-state-size': 'int',
             'date-sec': 'int', 'date-nsec': 'int',
-            'vm-clock-sec': 'int', 'vm-clock-nsec': 'int' } }
+            'vm-clock-sec': 'int', 'vm-clock-nsec': 'int',
+            '*icount': 'int' } }
 
 ##
 # @ImageInfoSpecificQCow2EncryptionBase:
diff --git a/qapi/block.json b/qapi/block.json
index 5a79d63..fd9c0ee 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -176,7 +176,8 @@
 #                    "date-sec": 1000012,
 #                    "date-nsec": 10,
 #                    "vm-clock-sec": 100,
-#                    "vm-clock-nsec": 20
+#                    "vm-clock-nsec": 20,
+#                    "icount": 220414
 #      }
 #    }
 #