Re: [Qemu-devel] [PATCH v2 14/17] block: Resize bitmaps on bdrv_truncate

[John Snow <jsnow@redhat.com>]

On 03/03/2015 11:02 AM, Max Reitz wrote:
> On 2015-03-02 at 18:20, John Snow wrote:
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   block.c                | 22 ++++++++++++++++++++
>>   include/block/block.h  |  1 +
>>   include/qemu/hbitmap.h | 10 +++++++++
>>   util/hbitmap.c         | 55
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>>   4 files changed, 88 insertions(+)
>>
>> diff --git a/block.c b/block.c
>> index e6b2696..5eaa874 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -3543,6 +3543,7 @@ int bdrv_truncate(BlockDriverState *bs, int64_t
>> offset)
>>       ret = drv->bdrv_truncate(bs, offset);
>>       if (ret == 0) {
>>           ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS);
>> +        bdrv_dirty_bitmap_truncate(bs);
>>           if (bs->blk) {
>>               blk_dev_resize_cb(bs->blk);
>>           }
>> @@ -5562,6 +5563,27 @@ BdrvDirtyBitmap
>> *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
>>       return parent;
>>   }
>> +static void dirty_bitmap_truncate(BdrvDirtyBitmap *bitmap, uint64_t
>> size)
>> +{
>> +    /* Should only be frozen during a block backup job, which should
>> have
>> +     * blocked any resize actions. */
>> +    assert(!bdrv_dirty_bitmap_frozen(bitmap));
>> +    hbitmap_truncate(bitmap->bitmap, size);
>> +}
>> +
>> +void bdrv_dirty_bitmap_truncate(BlockDriverState *bs)
>> +{
>> +    BdrvDirtyBitmap *bitmap;
>> +    uint64_t size = bdrv_nb_sectors(bs);
>> +
>> +    QLIST_FOREACH(bitmap, &bs->dirty_bitmaps, list) {
>> +        if (bdrv_dirty_bitmap_frozen(bitmap)) {
>> +            continue;
>> +        }
>
> Hm!
>
> The assert() above doesn't do anything because this condition will just
> skip over frozen bitmaps. Maybe we should drop it?
>
> I guess my R-b stands since bdrv_dirty_bitmap_frozen(bitmap) will always
> be false anyway (hence the assertion), but it would stand with this
> block dropped, too.
>
> Max
>

It's there for parity with the other bdrv helpers that perform a similar 
check. I am guarding against, in the future, any potential users from 
deciding to call this function directly for whichever reason.

Requesting an action on a drive that contains bitmaps that are not ready 
for the action is OK. Requesting an action on a bitmap that is not ready 
for the action should never happen, hence the 'documentation assert.'

My default action will be to leave it in.

--js


>> +        dirty_bitmap_truncate(bitmap, size);
>> +    }
>> +}
>> +
>>   void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap
>> *bitmap)
>>   {
>>       BdrvDirtyBitmap *bm, *next;
>> diff --git a/include/block/block.h b/include/block/block.h
>> index a8c6369..3a85690 100644
>> --- a/include/block/block.h
>> +++ b/include/block/block.h
>> @@ -454,6 +454,7 @@ BdrvDirtyBitmap
>> *bdrv_create_dirty_bitmap(BlockDriverState *bs,
>>                                             uint32_t granularity,
>>                                             const char *name,
>>                                             Error **errp);
>> +void bdrv_dirty_bitmap_truncate(BlockDriverState *bs);
>>   int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
>>                                          BdrvDirtyBitmap *bitmap,
>>                                          Error **errp);
>> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
>> index c19c1cb..a75157e 100644
>> --- a/include/qemu/hbitmap.h
>> +++ b/include/qemu/hbitmap.h
>> @@ -65,6 +65,16 @@ struct HBitmapIter {
>>   HBitmap *hbitmap_alloc(uint64_t size, int granularity);
>>   /**
>> + * hbitmap_truncate:
>> + * @hb: The bitmap to change the size of.
>> + * @size: The number of elements to change the bitmap to accommodate.
>> + *
>> + * truncate or grow an existing bitmap to accommodate a new number of
>> elements.
>> + * This may invalidate existing HBitmapIterators.
>> + */
>> +void hbitmap_truncate(HBitmap *hb, uint64_t size);
>> +
>> +/**
>>    * hbitmap_merge:
>>    * @a: The bitmap to store the result in.
>>    * @b: The bitmap to merge into @a.
>> diff --git a/util/hbitmap.c b/util/hbitmap.c
>> index 962ff29..dd8c2f3 100644
>> --- a/util/hbitmap.c
>> +++ b/util/hbitmap.c
>> @@ -90,6 +90,9 @@ struct HBitmap {
>>        * bitmap will still allocate HBITMAP_LEVELS arrays.
>>        */
>>       unsigned long *levels[HBITMAP_LEVELS];
>> +
>> +    /* The length of each levels[] array. */
>> +    uint64_t sizes[HBITMAP_LEVELS];
>>   };
>>   /* Advance hbi to the next nonzero word and return it.  hbi->pos
>> @@ -384,6 +387,7 @@ HBitmap *hbitmap_alloc(uint64_t size, int
>> granularity)
>>       hb->granularity = granularity;
>>       for (i = HBITMAP_LEVELS; i-- > 0; ) {
>>           size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
>> +        hb->sizes[i] = size;
>>           hb->levels[i] = g_new0(unsigned long, size);
>>       }
>> @@ -396,6 +400,57 @@ HBitmap *hbitmap_alloc(uint64_t size, int
>> granularity)
>>       return hb;
>>   }
>> +void hbitmap_truncate(HBitmap *hb, uint64_t size)
>> +{
>> +    bool truncate;
>> +    unsigned i;
>> +    uint64_t num_elements = size;
>> +    uint64_t old;
>> +
>> +    /* Size comes in as logical elements, adjust for granularity. */
>> +    size = (size + (1ULL << hb->granularity) - 1) >> hb->granularity;
>> +    assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
>> +    truncate = size < hb->size;
>> +
>> +    if (size == hb->size) {
>> +        /* A hard day's work */
>> +        return;
>> +    }
>> +
>> +    hb->size = size;
>> +    for (i = HBITMAP_LEVELS; i-- > 0; ) {
>> +        size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
>> +        if (hb->sizes[i] == size) {
>> +            continue;
>> +        }
>> +        old = hb->sizes[i];
>> +        hb->sizes[i] = size;
>> +        hb->levels[i] = g_realloc_n(hb->levels[i], size,
>> sizeof(unsigned long));
>> +        if (!truncate) {
>> +            memset(&hb->levels[i][old], 0x00,
>> +                   (size - old) * sizeof(*hb->levels[i]));
>> +        }
>> +    }
>> +    assert(size == 1);
>> +
>> +    /* Clear out any "extra space" we may have that the user didn't
>> request:
>> +     * It may have garbage data in it, now. */
>> +    if (truncate) {
>> +        /* Due to granularity fuzziness, we may accidentally reset
>> some of
>> +         * the last bits that are actually valid. So, record the
>> current value,
>> +         * reset the "dead range," then re-set the one element we
>> care about. */
>> +        uint64_t fix_count = (hb->size << hb->granularity) -
>> num_elements;
>> +        if (fix_count) {
>> +            bool set = hbitmap_get(hb, num_elements - 1);
>> +            hbitmap_reset(hb, num_elements, fix_count);
>> +            if (set) {
>> +                hbitmap_set(hb, num_elements - 1, 1);
>> +            }
>> +        }
>> +    }
>> +}
>> +
>> +
>>   /**
>>    * Given HBitmaps A and B, let A := A (BITOR) B.
>>    * Bitmap B will not be modified.
>