Patchwork [08/10] qcow2: Allow updating no refcounts

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Submitter Kevin Wolf
Date Jan. 18, 2010, 12:11 p.m.
Message ID <1263816696-24122-9-git-send-email-kwolf@redhat.com>
Download mbox | patch
Permalink /patch/43067/
State New
Headers show

Comments

Kevin Wolf - Jan. 18, 2010, 12:11 p.m.
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 <kwolf@redhat.com>
---
 block/qcow2-refcount.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
Christoph Hellwig - Jan. 19, 2010, 6:53 p.m.
>  #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?
Kevin Wolf - Jan. 20, 2010, 9:55 a.m.
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

Patch

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;