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Re: [Qemu-devel] [PATCH 5/8] block: use BlockDriverState refcnt for devi
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [PATCH 5/8] block: use BlockDriverState refcnt for device attach/detach |
Date: |
Thu, 25 Jul 2013 08:49:17 -0400 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Jul 25, 2013 at 05:01:43PM +0800, Fam Zheng wrote:
> Signed-off-by: Fam Zheng <address@hidden>
> ---
> block.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index dfa4be0..ce4d94b 100644
> --- a/block.c
> +++ b/block.c
> @@ -1620,11 +1620,13 @@ int bdrv_attach_dev(BlockDriverState *bs, void *dev)
> return -EBUSY;
> }
> bs->dev = dev;
> + bdrv_ref(bs);
> bdrv_iostatus_reset(bs);
> return 0;
> }
>
> -/* TODO qdevified devices don't use this, remove when devices are qdevified
> */
> +/* Attach a bs to dev, and increase its refcnt.
> + * TODO qdevified devices don't use this, remove when devices are qdevified
> */
> void bdrv_attach_dev_nofail(BlockDriverState *bs, void *dev)
> {
> if (bdrv_attach_dev(bs, dev) < 0) {
> @@ -1632,10 +1634,13 @@ void bdrv_attach_dev_nofail(BlockDriverState *bs,
> void *dev)
> }
> }
>
> +/* Detach bs from device. This decreases its refcnt, and may consequently
> + * deletes it make bs an invalid pointer */
> void bdrv_detach_dev(BlockDriverState *bs, void *dev)
> /* TODO change to DeviceState *dev when all users are qdevified */
> {
> assert(bs->dev == dev);
> + bdrv_unref(bs);
> bs->dev = NULL;
> bs->dev_ops = NULL;
> bs->dev_opaque = NULL;
This won't work, since we are dereferencing bs shortly after
(potentially) freeing it. I would say just move the bdrv_unref() to
the end of the function, but I have another concern as well.
If bs is freed, then BDS pointer is now invalid, but not NULL. So
there is no way for callers of bdrv_detach_dev() to know if the BDS
pointer they passed into bdrv_detach_dev() is still valid; in fact, I
think some call bdrv_close(bs) afterwards (piix). Qdev also still
uses it, although just for pointer comparison and not dereferencing.
Jeff
> --
> 1.8.3.2
>
>
[Qemu-devel] [PATCH 2/8] iscsi: use bdrv_new() instead of stack structure, Fam Zheng, 2013/07/25
[Qemu-devel] [PATCH 4/8] block: make bdrv_delete() static, Fam Zheng, 2013/07/25
[Qemu-devel] [PATCH 5/8] block: use BlockDriverState refcnt for device attach/detach, Fam Zheng, 2013/07/25
- Re: [Qemu-devel] [PATCH 5/8] block: use BlockDriverState refcnt for device attach/detach,
Jeff Cody <=
[Qemu-devel] [PATCH 6/8] migration: omit drive ref as we have bdrv_ref now, Fam Zheng, 2013/07/25
[Qemu-devel] [PATCH 7/8] xen_disk: simplify blk_disconnect with refcnt, Fam Zheng, 2013/07/25
[Qemu-devel] [PATCH 8/8] nbd: use BlockDriverState refcnt, Fam Zheng, 2013/07/25