[Qemu-devel] [RFC PATCH v2 06/19] qcow2: introduce icount field for snapshots

[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.Dovgaluk@ispras.ru>

--

v2:
 - documented format changes in docs/interop/qcow2.txt
   (suggested by Eric Blake)
---
 block/qcow2-snapshot.c |    7 +++++++
 block/qcow2.h          |    2 ++
 docs/interop/qcow2.txt |    4 ++++
 3 files changed, 13 insertions(+)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 74293be..d04553e 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -103,6 +103,12 @@ int qcow2_read_snapshots(BlockDriverState *bs)
             sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
         }
 
+        if (extra_data_size >= 24) {
+            sn->icount = be64_to_cpu(extra.icount);
+        } else {
+            sn->icount = -1ULL;
+        }
+
         /* Read snapshot ID */
         sn->id_str = g_malloc(id_str_size + 1);
         ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
@@ -209,6 +215,7 @@ static 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 adf5c39..8880937 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -151,6 +151,7 @@ typedef struct QEMU_PACKED QCowSnapshotHeader {
 typedef struct QEMU_PACKED QCowSnapshotExtraData {
     uint64_t vm_state_size_large;
     uint64_t disk_size;
+    uint64_t icount;
 } QCowSnapshotExtraData;
 
 
@@ -164,6 +165,7 @@ typedef struct QCowSnapshot {
     uint32_t date_sec;
     uint32_t date_nsec;
     uint64_t vm_clock_nsec;
+    uint64_t icount;
 } QCowSnapshot;
 
 struct Qcow2Cache;
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index feb711f..ff5b4ed 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -506,6 +506,10 @@ 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 step when the snapshot
+                                    was taken
+
                     Version 3 images must include extra data at least up to
                     byte 55.