[Qemu-devel] [PATCH v8 08/20] 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 rewinding
the recorded execution to the specific moment of the time.
E.g., 'reverse step' action needs to load the nearest snapshot which is
prior to the current moment of time .

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

--

v2:
 - made icount in SnapshotInfo optional (suggested by Eric Blake)
v7:
 - added more comments for icount member (suggested by Markus Armbruster)
---
 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 e6c8349..092e72e 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"
@@ -1241,6 +1242,10 @@ 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;
 
@@ -1449,6 +1454,11 @@ 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 9e45fb4..a031e5b 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2509,6 +2509,11 @@ 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 762000f..7bb1727 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 11f01f2..a6396a9 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
 #      }
 #    }
 #