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[Qemu-devel] [PATCH v3 1/3] dmg: fix binary search
From: |
yuchenlin |
Subject: |
[Qemu-devel] [PATCH v3 1/3] dmg: fix binary search |
Date: |
Thu, 3 Jan 2019 19:46:58 +0800 |
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 <address@hidden>
---
block/dmg.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/block/dmg.c b/block/dmg.c
index 50e91aef6d..65a0140487 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -572,16 +572,20 @@ static inline uint32_t search_chunk(BDRVDMGState *s,
uint64_t sector_num)
{
/* binary search */
uint32_t chunk1 = 0, chunk2 = s->n_chunks, chunk3;
- while (chunk1 != chunk2) {
+ while (chunk1 <= chunk2) {
chunk3 = (chunk1 + chunk2) / 2;
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) {
return chunk3;
} else {
- chunk1 = chunk3;
+ chunk1 = chunk3 + 1;
}
}
+err:
return s->n_chunks; /* error */
}
--
2.17.1