Typically, data for unallocated clusters is filled with zeros, so it makes no
sense to store it in the cache.
Signed-off-by: Pavel Butsykin <pbutsy...@virtuozzo.com>
---
block/pcache.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/block/pcache.c b/block/pcache.c
index 3717037..1f3800d 100644
--- a/block/pcache.c
+++ b/block/pcache.c
@@ -223,6 +223,28 @@ static RBCacheNode *pcache_node_alloc(uint64_t offset,
uint64_t bytes,
return &node->common;
}
+static bool check_allocated_clusters(BlockDriverState *bs, uint64_t offset,
+ uint64_t bytes)
+{
+ int64_t sector_num = offset >> BDRV_SECTOR_BITS;
+ int32_t nb_sectors = bytes >> BDRV_SECTOR_BITS;
+
+ assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
+ assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
+
+ do {
+ int num, ret = bdrv_is_allocated(bs, sector_num, nb_sectors, &num);
+ if (ret <= 0) {
+ return false;
+ }
+ sector_num += num;
+ nb_sectors -= num;
+
+ } while (nb_sectors);
+
+ return true;
+}
+
#define PCACHE_STEPS_FORWARD 2
static PCacheNode *get_readahead_node(BlockDriverState *bs, RBCache *rbcache,
@@ -242,6 +264,10 @@ static PCacheNode *get_readahead_node(BlockDriverState
*bs, RBCache *rbcache,
break;
}
+ if (!check_allocated_clusters(bs, offset, bytes)) {
+ break;
+ }
+
node = rbcache_search_and_insert(rbcache, offset, bytes);
if (node->status == NODE_STATUS_NEW) {
return node;
--
2.10.1
