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Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset
From: |
Kevin Wolf |
Subject: |
Re: [PULL 01/19] util/hbitmap: strict hbitmap_reset |
Date: |
Tue, 15 Oct 2019 10:44:43 +0200 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
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 <address@hidden>
> >>>
> >>> 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 <address@hidden>
> >>> Reviewed-by: Max Reitz <address@hidden>
> >>> Message-Id: <address@hidden>
> >>> [Maintainer edit: Max's suggestions from on-list. --js]
> >>> Signed-off-by: John Snow <address@hidden>
> >>> ---
> >>> 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?
Kevin
[PULL 02/19] block: move bdrv_can_store_new_dirty_bitmap to block/dirty-bitmap.c, John Snow, 2019/10/11
[PULL 03/19] block/dirty-bitmap: return int from bdrv_remove_persistent_dirty_bitmap, John Snow, 2019/10/11
[PULL 04/19] block/qcow2: proper locking on bitmap add/remove paths, John Snow, 2019/10/11
[PULL 05/19] block/dirty-bitmap: drop meta, John Snow, 2019/10/11
[PULL 07/19] block/dirty-bitmap: drop BdrvDirtyBitmap.mutex, John Snow, 2019/10/11
[PULL 06/19] block/dirty-bitmap: add bs link, John Snow, 2019/10/11
[PULL 08/19] block/dirty-bitmap: refactor bdrv_dirty_bitmap_next, John Snow, 2019/10/11
[PULL 09/19] block: switch reopen queue from QSIMPLEQ to QTAILQ, John Snow, 2019/10/11
[PULL 10/19] block: reverse order for reopen commits, John Snow, 2019/10/11