| Message ID | 1374742906-4489-4-git-send-email-famz@redhat.com |
|---|---|
| State | New |
| Headers | show |
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 <famz@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 > >
On Thu, 07/25 09:15, Jeff Cody wrote: > 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 <famz@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. > By calling bdrv_unref, it means the caller is not going to use bs any more. In other words, bdrv_unref() is a bdrv_delete() as seen by the caller, if bs is still valid pointer after unref, it's no longer safe for the caller: it can be freed by other code, in any time, but the caller can't know. > 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. > Yes, it can be omited. > > + > > 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 > > > >
On Fri, Jul 26, 2013 at 09:13:32AM +0800, Fam Zheng wrote: > On Thu, 07/25 09:15, Jeff Cody wrote: > > 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 <famz@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. > > > By calling bdrv_unref, it means the caller is not going to use bs any > more. In other words, bdrv_unref() is a bdrv_delete() as seen by the > caller, if bs is still valid pointer after unref, it's no longer safe > for the caller: it can be freed by other code, in any time, but the > caller can't know. OK, I can go with that. I can't think off the top of my head where this would cause a problem if it is just used in place of current bdrv_delete(), so long as everyone refs it when they should. But then going with a bdrv_delete() equivalency model, I don't know if it is appropriate to call bdrv_unref() in bdrv_detach_dev() (in patch 5/8). Maybe all that is really needed there is some more cleanup in the places that call bdrv_detach_dev(), and then it would be OK. > > > 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. > > > Yes, it can be omited. > > > > + > > > 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 > > > > > > > > -- > Fam
On Thu, 07/25 21:50, Jeff Cody wrote: > On Fri, Jul 26, 2013 at 09:13:32AM +0800, Fam Zheng wrote: > > On Thu, 07/25 09:15, Jeff Cody wrote: > > > 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 <famz@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. > > > > > By calling bdrv_unref, it means the caller is not going to use bs any > > more. In other words, bdrv_unref() is a bdrv_delete() as seen by the > > caller, if bs is still valid pointer after unref, it's no longer safe > > for the caller: it can be freed by other code, in any time, but the > > caller can't know. > > OK, I can go with that. I can't think off the top of my head where > this would cause a problem if it is just used in place of current > bdrv_delete(), so long as everyone refs it when they should. > > But then going with a bdrv_delete() equivalency model, I don't know if > it is appropriate to call bdrv_unref() in bdrv_detach_dev() (in patch > 5/8). Maybe all that is really needed there is some more cleanup in > the places that call bdrv_detach_dev(), and then it would be OK. Yes, you're right. I need to audit the device code yet. Thanks for pointing out. > > > > > 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. > > > > > Yes, it can be omited. > > > > > > + > > > > 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 > > > > > > > > > > > > -- > > Fam
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); + } +} + 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;
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 <famz@redhat.com> --- block.c | 22 ++++++++++++++++++++++ include/block/block.h | 2 ++ include/block/block_int.h | 1 + 3 files changed, 25 insertions(+)