Patchwork [12/12] block/get_block_status: fix BDRV_BLOCK_ZERO for unallocated blocks

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Submitter Peter Lieven
Date Sept. 13, 2013, 10:25 a.m.
Message ID <1379067909-22984-13-git-send-email-pl@kamp.de>
Download mbox | patch
Permalink /patch/274720/
State New
Headers show

Comments

Peter Lieven - Sept. 13, 2013, 10:25 a.m.
this patch does 2 things:
a) only do additional call outs if BDRV_BLOCK_ZERO is not already set.
b) use bdi.discard_zeroes to return the zero state of an unallocated block.
   the callout to bdrv_has_zero_init() is only valid right after bdrv_create.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 block.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
Eric Blake - Sept. 13, 2013, 1:53 p.m.
On 09/13/2013 04:25 AM, Peter Lieven wrote:
> this patch does 2 things:
> a) only do additional call outs if BDRV_BLOCK_ZERO is not already set.
> b) use bdi.discard_zeroes to return the zero state of an unallocated block.
>    the callout to bdrv_has_zero_init() is only valid right after bdrv_create.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 282943b..6698c10 100644
> --- a/block.c
> +++ b/block.c
> @@ -3153,8 +3153,10 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
>          return ret;
>      }
>  
> -    if (!(ret & BDRV_BLOCK_DATA)) {
> -        if (bdrv_has_zero_init(bs)) {
> +    if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {

Why not avoid the &&:

if ((ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) == 0) {

Then again, any decent compiler will probably already do that
optimization on your behalf.

> +        BlockDriverInfo bdi;
> +        if (bdrv_get_info(bs, &bdi) == 0 &&
> +            bdi.discard_zeroes) {
>              ret |= BDRV_BLOCK_ZERO;
>          } else if (bs->backing_hd) {
>              BlockDriverState *bs2 = bs->backing_hd;
>
Peter Lieven - Sept. 16, 2013, 5:47 a.m.
On 13.09.2013 12:25, Peter Lieven wrote:
> this patch does 2 things:
> a) only do additional call outs if BDRV_BLOCK_ZERO is not already set.
> b) use bdi.discard_zeroes to return the zero state of an unallocated block.
>     the callout to bdrv_has_zero_init() is only valid right after bdrv_create.
>
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>   block.c |    6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 282943b..6698c10 100644
> --- a/block.c
> +++ b/block.c
> @@ -3153,8 +3153,10 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
>           return ret;
>       }
>   
> -    if (!(ret & BDRV_BLOCK_DATA)) {
> -        if (bdrv_has_zero_init(bs)) {
> +    if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {
> +        BlockDriverInfo bdi;
> +        if (bdrv_get_info(bs, &bdi) == 0 &&
> +            bdi.discard_zeroes) {
>               ret |= BDRV_BLOCK_ZERO;
>           } else if (bs->backing_hd) {
>               BlockDriverState *bs2 = bs->backing_hd;
Kevin, according to your comment that we need a separate function like
bdrv_has_discard_zeroes. It should also be ok to change the order and
first check for bs->backing_hd here or not?

Peter

Patch

diff --git a/block.c b/block.c
index 282943b..6698c10 100644
--- a/block.c
+++ b/block.c
@@ -3153,8 +3153,10 @@  static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
         return ret;
     }
 
-    if (!(ret & BDRV_BLOCK_DATA)) {
-        if (bdrv_has_zero_init(bs)) {
+    if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {
+        BlockDriverInfo bdi;
+        if (bdrv_get_info(bs, &bdi) == 0 &&
+            bdi.discard_zeroes) {
             ret |= BDRV_BLOCK_ZERO;
         } else if (bs->backing_hd) {
             BlockDriverState *bs2 = bs->backing_hd;