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@xxxxxxxxxxxxx> >>> >>> 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@xxxxxxxxxxxxx> >>> Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx> >>> Message-Id: <20190806152611.280389-1-vsementsov@xxxxxxxxxxxxx> >>> [Maintainer edit: Max's suggestions from on-list. --js] >>> Signed-off-by: John Snow <jsnow@xxxxxxxxxx> >>> --- >>> 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. (You may feel free to counter-educate me as desired.) >> > > If the PR doesn't make it for some reason, I can amend a cleanup patch > for the next PR. > by the way: GOOD NEWS! ... --js -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
