On Thu, Jul 25, 2013 at 05:01:41PM +0800, Fam Zheng wrote: > Introduce bdrv_ref/bdrv_unref to manage the lifecycle of > BlockDriverState. They are unused for now but will used to replace > bdrv_delete() later. > > Signed-off-by: Fam Zheng <f...@redhat.com> > --- > block.c | 22 ++++++++++++++++++++++ > include/block/block.h | 2 ++ > include/block/block_int.h | 1 + > 3 files changed, 25 insertions(+) > > diff --git a/block.c b/block.c > index 6cd39fa..6f7ad7f 100644 > --- a/block.c > +++ b/block.c > @@ -306,6 +306,7 @@ BlockDriverState *bdrv_new(const char *device_name) > bdrv_iostatus_disable(bs); > notifier_list_init(&bs->close_notifiers); > notifier_with_return_list_init(&bs->before_write_notifiers); > + bs->refcnt = 1; > > return bs; > } > @@ -1511,6 +1512,9 @@ static void bdrv_move_feature_fields(BlockDriverState > *bs_dest, > /* dirty bitmap */ > bs_dest->dirty_bitmap = bs_src->dirty_bitmap; > > + /* reference count */ > + bs_dest->refcnt = bs_src->refcnt; > + > /* job */ > bs_dest->in_use = bs_src->in_use; > bs_dest->job = bs_src->job; > @@ -4385,6 +4389,24 @@ int64_t bdrv_get_dirty_count(BlockDriverState *bs) > } > } > > +/* Get a reference to bs */ > +void bdrv_ref(BlockDriverState *bs) > +{ > + bs->refcnt++; > +} > + > +/* Release a previously grabbed reference to bs. > + * If after releasing, reference count is zero, the BlockDriverState is > + * deleted. */ > +void bdrv_unref(BlockDriverState *bs) > +{ > + assert(bs->refcnt > 0); > + if (--bs->refcnt == 0) { > + bdrv_close(bs); > + bdrv_delete(bs); > + } > +}
The problem with this is that a caller to bdrv_unref() has no way of knowing after calling bdrv_unref() if bs is still valid. We can't just set bs to NULL after calling bdrv_unref() as with bdrv_delete(), because now it may not have been freed. Maybe bdrv_unref should either return the current bs pointer, or alternatively accept as its argument a pointer to the BDS pointer: void bdrv_unref(BlockDriverState **bs) { assert(*bs->refcnt > 0); if (--*bs->refcnt == 0) { bdrv_close(*bs); bdrv_delete(*bs); *bs = NULL; } } Of course, all callers would need to then check for NULL. Also, do we need to call bdrv_close() in here? In bdrv_delete(), bdrv_close() is called prior to the free. > + > void bdrv_set_in_use(BlockDriverState *bs, int in_use) > { > assert(bs->in_use != in_use); > diff --git a/include/block/block.h b/include/block/block.h > index 742fce5..b33ef62 100644 > --- a/include/block/block.h > +++ b/include/block/block.h > @@ -356,6 +356,8 @@ int64_t bdrv_get_dirty_count(BlockDriverState *bs); > void bdrv_enable_copy_on_read(BlockDriverState *bs); > void bdrv_disable_copy_on_read(BlockDriverState *bs); > > +void bdrv_ref(BlockDriverState *bs); > +void bdrv_unref(BlockDriverState *bs); > void bdrv_set_in_use(BlockDriverState *bs, int in_use); > int bdrv_in_use(BlockDriverState *bs); > > diff --git a/include/block/block_int.h b/include/block/block_int.h > index c6ac871..a282d56 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -294,6 +294,7 @@ struct BlockDriverState { > BlockDeviceIoStatus iostatus; > char device_name[32]; > HBitmap *dirty_bitmap; > + int refcnt; > int in_use; /* users other than guest access, eg. block migration */ > QTAILQ_ENTRY(BlockDriverState) list; > > -- > 1.8.3.2 > >