[Qemu-devel] [PATCH 3/7] block: fix snapshot with QED format

[Paolo Bonzini <pbonzini@redhat.com>]

QED's opaque data includes a pointer back to the BlockDriverState.
Creating a snapshot whose format is QED breaks the relationship when
bdrv_append shuffles data between bs_new and bs_top.  To avoid this,
add a "rebind" function that tells the driver about the new relationship
between the BlockDriverState and its opaque.

The patch also adds rebind to VVFAT for completeness, even though it is
not used with live snapshots.

Thanks to Stefan and Jeff for help reproducing and debugging this.

Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Jeff Cody <jcody@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block.c       |   10 ++++++++++
 block/qed.c   |    7 +++++++
 block/vvfat.c |    7 +++++++
 block_int.h   |    1 +
 4 files changed, 25 insertions(+)

diff --git a/block.c b/block.c
index b3117ef..a3a2e92 100644
--- a/block.c
+++ b/block.c
@@ -885,6 +885,13 @@ void bdrv_make_anon(BlockDriverState *bs)
     bs->device_name[0] = '\0';
 }
 
+static void bdrv_rebind(BlockDriverState *bs)
+{
+    if (bs->drv && bs->drv->bdrv_rebind) {
+        bs->drv->bdrv_rebind(bs);
+    }
+}
+
 /*
  * Add new bs contents at the top of an image chain while the chain is
  * live, while keeping required fields on the top layer.
@@ -973,6 +980,9 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top)
     bs_new->slice_time        = 0;
     bs_new->slice_start       = 0;
     bs_new->slice_end         = 0;
+
+    bdrv_rebind(bs_new);
+    bdrv_rebind(bs_top);
 }
 
 void bdrv_delete(BlockDriverState *bs)
diff --git a/block/qed.c b/block/qed.c
index 19d87f3..9364212 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -367,6 +367,12 @@ static void qed_cancel_need_check_timer(BDRVQEDState *s)
     qemu_del_timer(s->need_check_timer);
 }
 
+static void bdrv_qed_rebind(BlockDriverState *bs)
+{
+    BDRVQEDState *s = bs->opaque;
+    s->bs = bs;
+}
+
 static int bdrv_qed_open(BlockDriverState *bs, int flags)
 {
     BDRVQEDState *s = bs->opaque;
@@ -1549,6 +1555,7 @@ static BlockDriver bdrv_qed = {
     .create_options           = qed_create_options,
 
     .bdrv_probe               = bdrv_qed_probe,
+    .bdrv_rebind              = bdrv_qed_rebind,
     .bdrv_open                = bdrv_qed_open,
     .bdrv_close               = bdrv_qed_close,
     .bdrv_create              = bdrv_qed_create,
diff --git a/block/vvfat.c b/block/vvfat.c
index 9ef21dd..2dc9d50 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -982,6 +982,12 @@ static BDRVVVFATState *vvv = NULL;
 static int enable_write_target(BDRVVVFATState *s);
 static int is_consistent(BDRVVVFATState *s);
 
+static void vvfat_rebind(BlockDriverState *bs)
+{
+    BDRVVVFATState *s = bs->opaque;
+    s->bs = bs;
+}
+
 static int vvfat_open(BlockDriverState *bs, const char* dirname, int flags)
 {
     BDRVVVFATState *s = bs->opaque;
@@ -2855,6 +2861,7 @@ static BlockDriver bdrv_vvfat = {
     .format_name	= "vvfat",
     .instance_size	= sizeof(BDRVVVFATState),
     .bdrv_file_open	= vvfat_open,
+    .bdrv_rebind	= vvfat_rebind,
     .bdrv_read          = vvfat_co_read,
     .bdrv_write         = vvfat_co_write,
     .bdrv_close		= vvfat_close,
diff --git a/block_int.h b/block_int.h
index 0e5a032..58e3eea 100644
--- a/block_int.h
+++ b/block_int.h
@@ -139,6 +139,7 @@ struct BlockDriver {
     int (*bdrv_write)(BlockDriverState *bs, int64_t sector_num,
                       const uint8_t *buf, int nb_sectors);
     void (*bdrv_close)(BlockDriverState *bs);
+    void (*bdrv_rebind)(BlockDriverState *bs);
     int (*bdrv_create)(const char *filename, QEMUOptionParameter *options);
     int (*bdrv_set_key)(BlockDriverState *bs, const char *key);
     int (*bdrv_make_empty)(BlockDriverState *bs);
-- 
1.7.9.3