[PATCH v2 03/14] qcow2: introduce icount field for snapshots

[Pavel Dovgalyuk]

From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

This patch introduces the icount field for saving within the snapshot.
It is required for navigation between the snapshots in record/replay mode.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Acked-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2-snapshot.c |    7 +++++++
 block/qcow2.h          |    3 +++
 docs/interop/qcow2.txt |    5 +++++
 3 files changed, 15 insertions(+)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 2756b37d24..d14e7be1aa 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -164,6 +164,12 @@ static int qcow2_do_read_snapshots(BlockDriverState *bs, 
bool repair,
             sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
         }
 
+        if (sn->extra_data_size >= endof(QCowSnapshotExtraData, icount)) {
+            sn->icount = be64_to_cpu(extra.icount);
+        } else {
+            sn->icount = -1ULL;
+        }
+
         if (sn->extra_data_size > sizeof(extra)) {
             uint64_t extra_data_end;
             size_t unknown_extra_data_size;
@@ -333,6 +339,7 @@ int qcow2_write_snapshots(BlockDriverState *bs)
         memset(&extra, 0, sizeof(extra));
         extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
         extra.disk_size = cpu_to_be64(sn->disk_size);
+        extra.icount = cpu_to_be64(sn->icount);
 
         id_str_size = strlen(sn->id_str);
         name_size = strlen(sn->name);
diff --git a/block/qcow2.h b/block/qcow2.h
index 7ce2c23bdb..9c81086991 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -179,6 +179,7 @@ typedef struct QEMU_PACKED QCowSnapshotHeader {
 typedef struct QEMU_PACKED QCowSnapshotExtraData {
     uint64_t vm_state_size_large;
     uint64_t disk_size;
+    uint64_t icount;
 } QCowSnapshotExtraData;
 
 
@@ -192,6 +193,8 @@ typedef struct QCowSnapshot {
     uint32_t date_sec;
     uint32_t date_nsec;
     uint64_t vm_clock_nsec;
+    /* icount value for the moment when snapshot was taken */
+    uint64_t icount;
     /* Size of all extra data, including QCowSnapshotExtraData if available */
     uint32_t extra_data_size;
     /* Data beyond QCowSnapshotExtraData, if any */
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index f072e27900..3dc4b9f89a 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -645,6 +645,11 @@ Snapshot table entry:
 
                     Byte 48 - 55:   Virtual disk size of the snapshot in bytes
 
+                    Byte 56 - 63:   icount value which corresponds to
+                                    the record/replay instruction count
+                                    when the snapshot was taken. Set to -1
+                                    if icount was disabled
+
                     Version 3 images must include extra data at least up to
                     byte 55.