Re: [Qemu-devel] [PATCH 08/10] qcow2: Allow updating no refcounts

[Kevin Wolf]

Am 19.01.2010 19:53, schrieb Christoph Hellwig:
  #endif
 -if (length = 0)
 +if (length  0) {
  return -EINVAL;
 +}
 +
  start = offset  ~(s-cluster_size - 1);
  last = (offset + length - 1)  ~(s-cluster_size - 1);
  for(cluster_offset = start; cluster_offset = last;
 
 So for legnth = 0, last will equal start and we'll never go through
 the loop.  But should we really bother with all the other work in the
 function or just return 0 early on?

I'm not a big fan of special-casing for no real reason (all the other
work basically is calculating start and last and skipping two ifs - and
length = 0 is an unusual case anyway), but if you really mind we can
change it.

Kevin

Re: [Qemu-devel] [PATCH 08/10] qcow2: Allow updating no refcounts

[Christoph Hellwig]

  #endif
 -if (length = 0)
 +if (length  0) {
  return -EINVAL;
 +}
 +
  start = offset  ~(s-cluster_size - 1);
  last = (offset + length - 1)  ~(s-cluster_size - 1);
  for(cluster_offset = start; cluster_offset = last;

So for legnth = 0, last will equal start and we'll never go through
the loop.  But should we really bother with all the other work in the
function or just return 0 early on?

[Qemu-devel] [PATCH 08/10] qcow2: Allow updating no refcounts

[Kevin Wolf]

There's absolutely no problem with updating the refcounts of 0 clusters.
At least snapshot code is doing this and would fail once the result of
update_refcount isn't ignored any more.

Signed-off-by: Kevin Wolf kw...@redhat.com
---
 block/qcow2-refcount.c |4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index a84620f..3dfadf1 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -284,8 +284,10 @@ static int update_refcount(BlockDriverState *bs,
 printf(update_refcount: offset=% PRId64  size=% PRId64  addend=%d\n,
offset, length, addend);
 #endif
-if (length = 0)
+if (length  0) {
 return -EINVAL;
+}
+
 start = offset  ~(s-cluster_size - 1);
 last = (offset + length - 1)  ~(s-cluster_size - 1);
 for(cluster_offset = start; cluster_offset = last;
-- 
1.6.2.5