[Qemu-devel] [PATCH 0/2] block/vhdx: Small cleanups

[Qemu-devel] [PATCH 0/2] block/vhdx: Small cleanups

[Max Reitz]

Just some bits I discovered while going through the Coverity report.

(The issue reported by Coverity actually was not an issue.)


Max Reitz (2):
  vhdx: DIV_ROUND_UP() in vhdx_calc_bat_entries()
  vhdx: Simplify vhdx_set_shift_bits()

 block/vhdx.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

-- 
2.6.4

[Qemu-devel] [PATCH 1/2] vhdx: DIV_ROUND_UP() in vhdx_calc_bat_entries()

[Max Reitz]

We have DIV_ROUND_UP(), so we can use it to produce more easily readable
code. It may be slower than the bit shifting currently performed
(because it actually performs a division), but since
vhdx_calc_bat_entries() is never used in a hot path, this is completely
fine.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/vhdx.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/block/vhdx.c b/block/vhdx.c
index 2fe9a5e..3955f7f 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -856,14 +856,8 @@ static void vhdx_calc_bat_entries(BDRVVHDXState *s)
 {
     uint32_t data_blocks_cnt, bitmap_blocks_cnt;
 
-    data_blocks_cnt = s->virtual_disk_size >> s->block_size_bits;
-    if (s->virtual_disk_size - (data_blocks_cnt << s->block_size_bits)) {
-        data_blocks_cnt++;
-    }
-    bitmap_blocks_cnt = data_blocks_cnt >> s->chunk_ratio_bits;
-    if (data_blocks_cnt - (bitmap_blocks_cnt << s->chunk_ratio_bits)) {
-        bitmap_blocks_cnt++;
-    }
+    data_blocks_cnt = DIV_ROUND_UP(s->virtual_disk_size, s->block_size);
+    bitmap_blocks_cnt = DIV_ROUND_UP(data_blocks_cnt, s->chunk_ratio);
 
     if (s->parent_entries) {
         s->bat_entries = bitmap_blocks_cnt * (s->chunk_ratio + 1);
-- 
2.6.4

[Qemu-devel] [PATCH 2/2] vhdx: Simplify vhdx_set_shift_bits()

[Max Reitz]

For values which are powers of two (and we do assume all of these to
be), sizeof(x) * 8 - 1 - clz(x) == ctz(x). Therefore, use ctz().

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/vhdx.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/vhdx.c b/block/vhdx.c
index 3955f7f..475f602 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -263,10 +263,10 @@ static void vhdx_region_unregister_all(BDRVVHDXState *s)
 
 static void vhdx_set_shift_bits(BDRVVHDXState *s)
 {
-    s->logical_sector_size_bits = 31 - clz32(s->logical_sector_size);
-    s->sectors_per_block_bits =   31 - clz32(s->sectors_per_block);
-    s->chunk_ratio_bits =         63 - clz64(s->chunk_ratio);
-    s->block_size_bits =          31 - clz32(s->block_size);
+    s->logical_sector_size_bits = ctz32(s->logical_sector_size);
+    s->sectors_per_block_bits =   ctz32(s->sectors_per_block);
+    s->chunk_ratio_bits =         ctz64(s->chunk_ratio);
+    s->block_size_bits =          ctz32(s->block_size);
 }
 
 /*
-- 
2.6.4

Re: [Qemu-devel] [PATCH 0/2] block/vhdx: Small cleanups

[Max Reitz]

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On 18.12.2015 16:04, Max Reitz wrote:
> Just some bits I discovered while going through the Coverity report.
> 
> (The issue reported by Coverity actually was not an issue.)
> 
> 
> Max Reitz (2):
>   vhdx: DIV_ROUND_UP() in vhdx_calc_bat_entries()
>   vhdx: Simplify vhdx_set_shift_bits()
> 
>  block/vhdx.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)

Ping


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Re: [Qemu-devel] [PATCH 0/2] block/vhdx: Small cleanups

[Jeff Cody]

On Mon, Feb 22, 2016 at 06:39:48PM +0100, Max Reitz wrote:
> On 18.12.2015 16:04, Max Reitz wrote:
> > Just some bits I discovered while going through the Coverity report.
> > 
> > (The issue reported by Coverity actually was not an issue.)
> > 
> > 
> > Max Reitz (2):
> >   vhdx: DIV_ROUND_UP() in vhdx_calc_bat_entries()
> >   vhdx: Simplify vhdx_set_shift_bits()
> > 
> >  block/vhdx.c | 18 ++++++------------
> >  1 file changed, 6 insertions(+), 12 deletions(-)
> 
> Ping
> 

Thanks, applied to my block branch

Jeff