On 10/15/19 4:44 AM, Kevin Wolf wrote:
Am 14.10.2019 um 20:10 hat John Snow geschrieben:
On 10/11/19 7:18 PM, John Snow wrote:
On 10/11/19 5:48 PM, Eric Blake wrote:
On 10/11/19 4:25 PM, John Snow wrote:
From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
hbitmap_reset has an unobvious property: it rounds requested region up. It may provoke bugs, like in recently fixed write-blocking mode of mirror: user calls reset on unaligned region, not keeping in mind that there are possible unrelated dirty bytes, covered by rounded-up region and information of this unrelated "dirtiness" will be lost.
Make hbitmap_reset strict: assert that arguments are aligned, allowing only one exception when @start + @count == hb->orig_size. It's needed to comfort users of hbitmap_next_dirty_area, which cares about hb->orig_size.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20190806152611.280389-1-vsementsov@virtuozzo.com> [Maintainer edit: Max's suggestions from on-list. --js] Signed-off-by: John Snow <jsnow@redhat.com> --- include/qemu/hbitmap.h | 5 +++++ tests/test-hbitmap.c | 2 +- util/hbitmap.c | 4 ++++ 3 files changed, 10 insertions(+), 1 deletion(-)
+++ b/util/hbitmap.c @@ -476,6 +476,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count) /* Compute range in the last layer. */ uint64_t first; uint64_t last = start + count - 1; + uint64_t gran = 1ULL << hb->granularity; + + assert(!(start & (gran - 1))); + assert(!(count & (gran - 1)) || (start + count == hb->orig_size));
I know I'm replying a bit late (since this is now a pull request), but would it be worth using the dedicated macro:
assert(QEMU_IS_ALIGNED(start, gran)); assert(QEMU_IS_ALIGNED(count, gran) || start + count == hb->orig_size);
instead of open-coding it? (I would also drop the extra () around the right half of ||). If we want it, that would now be a followup patch.
I've noticed that seasoned C programmers hate extra parentheses a lot. I've noticed that I cannot remember operator precedence enough to ever feel like this is actually an improvement.
Something about a nice weighted tree of ((expr1) || (expr2)) feels soothing to my weary eyes. So, if it's not terribly important, I'd prefer to leave it as-is.
I don't mind the parentheses, but I do prefer QEMU_IS_ALIGNED() to the open-coded version. Would that be a viable compromise?
Oh, I'm sorry! I did change that. I didn't mean to appear any more stubborn than I actually am. --js