[v4,16/38] block: Add BlockBackendRootState

diff --git a/block/block-backend.c b/block/block-backend.c
index 0672ce7..b4a158d 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -13,6 +13,7 @@ 
 #include "sysemu/block-backend.h"
 #include "block/block_int.h"
 #include "block/blockjob.h"
+#include "block/throttle-groups.h"
 #include "sysemu/blockdev.h"
 #include "sysemu/sysemu.h"
 #include "qapi-event.h"
@@ -37,6 +38,10 @@  struct BlockBackend {
     /* the block size for which the guest device expects atomicity */
     int guest_block_size;
 
+    /* If the BDS tree is removed, some of its options are stored here (which
+     * can be used to restore those options in the new BDS on insert) */
+    BlockBackendRootState root_state;
+
     /* I/O stats (display with "info blockstats"). */
     BlockAcctStats stats;
 
@@ -161,6 +166,7 @@  static void blk_delete(BlockBackend *blk)
         bdrv_unref(blk->bs);
         blk->bs = NULL;
     }
+    g_free(blk->root_state.throttle_group_name);
     /* Avoid double-remove after blk_hide_on_behalf_of_hmp_drive_del() */
     if (blk->name[0]) {
         QTAILQ_REMOVE(&blk_backends, blk, link);
@@ -1050,3 +1056,34 @@  int blk_probe_geometry(BlockBackend *blk, HDGeometry *geo)
 {
     return bdrv_probe_geometry(blk->bs, geo);
 }
+
+/*
+ * Updates the BlockBackendRootState object with data from the currently
+ * attached BlockDriverState.
+ */
+void blk_update_root_state(BlockBackend *blk)
+{
+    assert(blk->bs);
+
+    blk->root_state.open_flags    = blk->bs->open_flags;
+    blk->root_state.read_only     = blk->bs->read_only;
+    blk->root_state.detect_zeroes = blk->bs->detect_zeroes;
+
+    blk->root_state.io_limits_enabled = blk->bs->io_limits_enabled;
+
+    g_free(blk->root_state.throttle_group_name);
+    if (blk->bs->throttle_state) {
+        throttle_get_config(blk->bs->throttle_state,
+                            &blk->root_state.throttle_config);
+        blk->root_state.throttle_group_name =
+            g_strdup(throttle_group_get_name(blk->bs));
+    } else {
+        blk->root_state.throttle_config = (ThrottleConfig){};
+        blk->root_state.throttle_group_name = NULL;
+    }
+}
+
+BlockBackendRootState *blk_get_root_state(BlockBackend *blk)
+{
+    return &blk->root_state;
+}
diff --git a/include/block/block_int.h b/include/block/block_int.h
index bd35570..ca1eefa 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -449,6 +449,16 @@  struct BlockDriverState {
     NotifierWithReturn write_threshold_notifier;
 };
 
+struct BlockBackendRootState {
+    int open_flags;
+    bool read_only;
+    BlockdevDetectZeroesOptions detect_zeroes;
+
+    bool io_limits_enabled;
+    ThrottleConfig throttle_config;
+    char *throttle_group_name;
+};
+
 
 /* Essential block drivers which must always be statically linked into qemu, and
  * which therefore can be accessed without using bdrv_find_format() */
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 6fdcbcd..413ac6e 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -11,6 +11,7 @@  typedef struct AddressSpace AddressSpace;
 typedef struct AioContext AioContext;
 typedef struct AudioState AudioState;
 typedef struct BlockBackend BlockBackend;
+typedef struct BlockBackendRootState BlockBackendRootState;
 typedef struct BlockDriverState BlockDriverState;
 typedef struct BusClass BusClass;
 typedef struct BusState BusState;
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index eafcef0..52e35a1 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -163,6 +163,8 @@  void blk_add_close_notifier(BlockBackend *blk, Notifier *notify);
 void blk_io_plug(BlockBackend *blk);
 void blk_io_unplug(BlockBackend *blk);
 BlockAcctStats *blk_get_stats(BlockBackend *blk);
+BlockBackendRootState *blk_get_root_state(BlockBackend *blk);
+void blk_update_root_state(BlockBackend *blk);
 
 void *blk_aio_get(const AIOCBInfo *aiocb_info, BlockBackend *blk,
                   BlockCompletionFunc *cb, void *opaque);