[v6,08/14] replay: implement replay-seek command

diff --git a/hmp-commands.hx b/hmp-commands.hx
index ced47e49d5..1981bf0511 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1851,6 +1851,24 @@  SRST
   The command is ignored when there are no replay breakpoints.
 ERST
 
+    {
+        .name       = "replay_seek",
+        .args_type  = "icount:i",
+        .params     = "icount",
+        .help       = "replay execution to the specified instruction count",
+        .cmd        = hmp_replay_seek,
+    },
+
+SRST
+``replay_seek`` *icount*
+  Automatically proceed to the instruction count *icount*, when
+  replaying the execution. The command automatically loads nearest
+  snapshot and replays the execution to find the desired instruction.
+  When there is no preceding snapshot or the execution is not replayed,
+  then the command fails.
+  *icount* for the reference may be observed with ``info replay`` command.
+ERST
+
     {
         .name       = "info",
         .args_type  = "item:s?",
diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
index 21849bdda5..655eb81a4c 100644
--- a/include/monitor/hmp.h
+++ b/include/monitor/hmp.h
@@ -133,5 +133,6 @@  void hmp_info_sev(Monitor *mon, const QDict *qdict);
 void hmp_info_replay(Monitor *mon, const QDict *qdict);
 void hmp_replay_break(Monitor *mon, const QDict *qdict);
 void hmp_replay_delete_break(Monitor *mon, const QDict *qdict);
+void hmp_replay_seek(Monitor *mon, const QDict *qdict);
 
 #endif
diff --git a/qapi/replay.json b/qapi/replay.json
index 173ba76107..bfd83d7591 100644
--- a/qapi/replay.json
+++ b/qapi/replay.json
@@ -99,3 +99,23 @@ 
 #
 ##
 { 'command': 'replay-delete-break' }
+
+##
+# @replay-seek:
+#
+# Automatically proceed to the instruction count @icount, when
+# replaying the execution. The command automatically loads nearest
+# snapshot and replays the execution to find the desired instruction.
+# When there is no preceding snapshot or the execution is not replayed,
+# then the command fails.
+# icount for the reference may be obtained with @query-replay command.
+#
+# @icount: target instruction count
+#
+# Since: 5.2
+#
+# Example:
+#
+# -> { "execute": "replay-seek", "data": { "icount": 220414 } }
+##
+{ 'command': 'replay-seek', 'data': { 'icount': 'int' } }
diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
index 3dc23b84fc..e1fe6b8661 100644
--- a/replay/replay-debugging.c
+++ b/replay/replay-debugging.c
@@ -19,6 +19,8 @@ 
 #include "qapi/qapi-commands-replay.h"
 #include "qapi/qmp/qdict.h"
 #include "qemu/timer.h"
+#include "block/snapshot.h"
+#include "migration/snapshot.h"
 
 void hmp_info_replay(Monitor *mon, const QDict *qdict)
 {
@@ -125,3 +127,88 @@  void hmp_replay_delete_break(Monitor *mon, const QDict *qdict)
         return;
     }
 }
+
+static char *replay_find_nearest_snapshot(int64_t icount,
+                                          int64_t *snapshot_icount)
+{
+    BlockDriverState *bs;
+    QEMUSnapshotInfo *sn_tab;
+    QEMUSnapshotInfo *nearest = NULL;
+    char *ret = NULL;
+    int nb_sns, i;
+    AioContext *aio_context;
+
+    *snapshot_icount = -1;
+
+    bs = bdrv_all_find_vmstate_bs();
+    if (!bs) {
+        goto fail;
+    }
+    aio_context = bdrv_get_aio_context(bs);
+
+    aio_context_acquire(aio_context);
+    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
+    aio_context_release(aio_context);
+
+    for (i = 0; i < nb_sns; i++) {
+        if (bdrv_all_find_snapshot(sn_tab[i].name, &bs) == 0) {
+            if (sn_tab[i].icount != -1ULL
+                && sn_tab[i].icount <= icount
+                && (!nearest || nearest->icount < sn_tab[i].icount)) {
+                nearest = &sn_tab[i];
+            }
+        }
+    }
+    if (nearest) {
+        ret = g_strdup(nearest->name);
+        *snapshot_icount = nearest->icount;
+    }
+    g_free(sn_tab);
+
+fail:
+    return ret;
+}
+
+static void replay_seek(int64_t icount, QEMUTimerCB callback, Error **errp)
+{
+    char *snapshot = NULL;
+    int64_t snapshot_icount;
+
+    if (replay_mode != REPLAY_MODE_PLAY) {
+        error_setg(errp, "replay must be enabled to seek");
+        return;
+    }
+
+    snapshot = replay_find_nearest_snapshot(icount, &snapshot_icount);
+    if (snapshot) {
+        if (icount < replay_get_current_icount()
+            || replay_get_current_icount() < snapshot_icount) {
+            vm_stop(RUN_STATE_RESTORE_VM);
+            load_snapshot(snapshot, errp);
+        }
+        g_free(snapshot);
+    }
+    if (replay_get_current_icount() <= icount) {
+        replay_break(icount, callback, NULL);
+        vm_start();
+    } else {
+        error_setg(errp, "cannot seek to the specified instruction count");
+    }
+}
+
+void qmp_replay_seek(int64_t icount, Error **errp)
+{
+    replay_seek(icount, replay_stop_vm, errp);
+}
+
+void hmp_replay_seek(Monitor *mon, const QDict *qdict)
+{
+    int64_t icount = qdict_get_try_int(qdict, "icount", -1LL);
+    Error *err = NULL;
+
+    qmp_replay_seek(icount, &err);
+    if (err) {
+        error_report_err(err);
+        return;
+    }
+}