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qcow2: Fix Coverity warning when calculating the refcount cache size 

MIN_REFCOUNT_CACHE_SIZE is 4 and the cluster size is guaranteed to be
at most 2MB, so the minimum refcount cache size (in bytes) is always
going to fit in a 32-bit integer.

Coverity doesn't know that, and since we're storing the result in a
uint64_t (*refcount_cache_size) it thinks that we need the 64 bits and
that we probably want to do a 64-bit multiplication to prevent the
result from being truncated.

This is a false positive in this case, but it's a fair warning.
We could do a 64-bit multiplication to get rid of it, but since we
know that a 32-bit variable is enough to store this value let's simply
reuse min_refcount_cache, make it a normal int and stop doing casts.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
master
Alberto Garcia 2018-05-28 17:01:28 +02:00 committed by Kevin Wolf
parent e609fa71e8
commit 7af5eea9b3
1 changed files with 2 additions and 3 deletions
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5
block/qcow2.c
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@ -768,6 +768,7 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
BDRVQcow2State *s = bs->opaque;
uint64_t combined_cache_size;
bool l2_cache_size_set, refcount_cache_size_set, combined_cache_size_set;
int min_refcount_cache = MIN_REFCOUNT_CACHE_SIZE * s->cluster_size;
combined_cache_size_set = qemu_opt_get(opts, QCOW2_OPT_CACHE_SIZE);
l2_cache_size_set = qemu_opt_get(opts, QCOW2_OPT_L2_CACHE_SIZE);
@ -804,8 +805,6 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
} else {
uint64_t virtual_disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
uint64_t max_l2_cache = virtual_disk_size / (s->cluster_size / 8);
uint64_t min_refcount_cache =
(uint64_t) MIN_REFCOUNT_CACHE_SIZE * s->cluster_size;
/* Assign as much memory as possible to the L2 cache, and
* use the remainder for the refcount cache */
@ -825,7 +824,7 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
* s->cluster_size);
}
if (!refcount_cache_size_set) {
*refcount_cache_size = MIN_REFCOUNT_CACHE_SIZE * s->cluster_size;
*refcount_cache_size = min_refcount_cache;
}
}