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hbitmap: Add hbitmap_is_serializable()

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Bitmaps with a granularity of 58 or above can be neither serialized nor
deserialized (see the comment in the function added in this series for
an explanation). This patch adds a function so that we can check whether
a bitmap actually can be (de-)serialized at all, thus avoiding failing
the necessary assertion in hbitmap_serialization_granularity().

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20161115225746.3590-2-mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
This commit is contained in:
Max Reitz 2016-11-15 23:57:45 +01:00 • committed by Fam Zheng
parent c7f1cf01b8
commit 20a579de84
2 changed files with 32 additions and 3 deletions
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22
util/hbitmap.c
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@ -387,6 +387,24 @@ void hbitmap_reset_all(HBitmap *hb)
hb->count = 0;
}
bool hbitmap_is_serializable(const HBitmap *hb)
{
/* Every serialized chunk must be aligned to 64 bits so that endianness
* requirements can be fulfilled on both 64 bit and 32 bit hosts.
* We have hbitmap_serialization_granularity() which converts this
* alignment requirement from bitmap bits to items covered (e.g. sectors).
* That value is:
* 64 << hb->granularity
* Since this value must not exceed UINT64_MAX, hb->granularity must be
* less than 58 (== 64 - 6, where 6 is ld(64), i.e. 1 << 6 == 64).
*
* In order for hbitmap_serialization_granularity() to always return a
* meaningful value, bitmaps that are to be serialized must have a
* granularity of less than 58. */
return hb->granularity < 58;
}
bool hbitmap_get(const HBitmap *hb, uint64_t item)
{
/* Compute position and bit in the last layer. */
@ -399,9 +417,7 @@ bool hbitmap_get(const HBitmap *hb, uint64_t item)
uint64_t hbitmap_serialization_granularity(const HBitmap *hb)
{
/* Must hold true so that the shift below is defined
* (ld(64) == 6, i.e. 1 << 6 == 64) */
assert(hb->granularity < 64 - 6);
assert(hbitmap_is_serializable(hb));
/* Require at least 64 bit granularity to be safe on both 64 bit and 32 bit
* hosts. */