[v2] block: Fix dst reading after tail copy offloading

[Qemu-devel] [PATCH v2 8/9] block: Fix bdrv_co_truncate overlap check

Posted by Fam Zheng 7 years, 4 months ago

If we are growing the image and potentially using preallocation for the
new area, we need to make sure that no write requests are made to the
"preallocated" area which [@old_size, @offset), not [@offset, offset * 2
- @old_size).

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/io.c b/block/io.c
index d07849fa96..ed18eb0ca3 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3070,7 +3070,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
     }
 
     bdrv_inc_in_flight(bs);
-    tracked_request_begin(&req, bs, offset, new_bytes, BDRV_TRACKED_TRUNCATE);
+    tracked_request_begin(&req, bs, offset - new_bytes, new_bytes,
+                          BDRV_TRACKED_TRUNCATE);
 
     /* If we are growing the image and potentially using preallocation for the
      * new area, we need to make sure that no write requests are made to it
-- 
2.17.1

Re: [Qemu-devel] [PATCH v2 8/9] block: Fix bdrv_co_truncate overlap check

Posted by Eric Blake 7 years, 4 months ago

On 07/05/2018 02:37 AM, Fam Zheng wrote:
> If we are growing the image and potentially using preallocation for the
> new area, we need to make sure that no write requests are made to the
> "preallocated" area which [@old_size, @offset), not [@offset, offset * 2

s/which/which is/

> - @old_size).
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   block/io.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> diff --git a/block/io.c b/block/io.c
> index d07849fa96..ed18eb0ca3 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -3070,7 +3070,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
>       }
>   
>       bdrv_inc_in_flight(bs);
> -    tracked_request_begin(&req, bs, offset, new_bytes, BDRV_TRACKED_TRUNCATE);
> +    tracked_request_begin(&req, bs, offset - new_bytes, new_bytes,
> +                          BDRV_TRACKED_TRUNCATE);

Is it any more legible to do s/offset - new_bytes/old_size/, since those 
are equivalent?

>   
>       /* If we are growing the image and potentially using preallocation for the
>        * new area, we need to make sure that no write requests are made to it
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH v2 8/9] block: Fix bdrv_co_truncate overlap check

Posted by Fam Zheng 7 years, 3 months ago

On Fri, 07/06 17:09, Eric Blake wrote:
> On 07/05/2018 02:37 AM, Fam Zheng wrote:
> > If we are growing the image and potentially using preallocation for the
> > new area, we need to make sure that no write requests are made to the
> > "preallocated" area which [@old_size, @offset), not [@offset, offset * 2
> 
> s/which/which is/
> 
> > - @old_size).
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >   block/io.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> > 
> > diff --git a/block/io.c b/block/io.c
> > index d07849fa96..ed18eb0ca3 100644
> > --- a/block/io.c
> > +++ b/block/io.c
> > @@ -3070,7 +3070,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
> >       }
> >       bdrv_inc_in_flight(bs);
> > -    tracked_request_begin(&req, bs, offset, new_bytes, BDRV_TRACKED_TRUNCATE);
> > +    tracked_request_begin(&req, bs, offset - new_bytes, new_bytes,
> > +                          BDRV_TRACKED_TRUNCATE);
> 
> Is it any more legible to do s/offset - new_bytes/old_size/, since those are
> equivalent?

No they are not. offset - new_bytes is either old_size (if expanding), or
smaller than old_size (if shrinking).

Fam

> 
> >       /* If we are growing the image and potentially using preallocation for the
> >        * new area, we need to make sure that no write requests are made to it
> > 
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org