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dmg: fix binary search

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There is a possible hang in original binary search implementation. That is
if chunk1 = 4, chunk2 = 5, chunk3 = 4, and we go else case.

The chunk1 will be still 4, and so on.

Signed-off-by: yuchenlin <npes87184@gmail.com>
Message-id: 20190103114700.9686-2-npes87184@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
yuchenlin 2019-01-03 19:46:58 +08:00 committed by Stefan Hajnoczi
parent b47c7d5325
commit 5ef40828ba
1 changed files with 7 additions and 3 deletions
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10
block/dmg.c
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@ -572,16 +572,20 @@ static inline uint32_t search_chunk(BDRVDMGState *s, uint64_t sector_num)
{ {
/* binary search */ /* binary search */
uint32_t chunk1 = 0, chunk2 = s->n_chunks, chunk3; uint32_t chunk1 = 0, chunk2 = s->n_chunks, chunk3;
while (chunk1 != chunk2) { while (chunk1 <= chunk2) {
chunk3 = (chunk1 + chunk2) / 2; chunk3 = (chunk1 + chunk2) / 2;
if (s->sectors[chunk3] > sector_num) { if (s->sectors[chunk3] > sector_num) {
chunk2 = chunk3; if (chunk3 == 0) {
goto err;
}
chunk2 = chunk3 - 1;
} else if (s->sectors[chunk3] + s->sectorcounts[chunk3] > sector_num) { } else if (s->sectors[chunk3] + s->sectorcounts[chunk3] > sector_num) {
return chunk3; return chunk3;
} else { } else {
chunk1 = chunk3; chunk1 = chunk3 + 1;
} }
} }
err:
return s->n_chunks; /* error */ return s->n_chunks; /* error */
} }