From 70d1cbae03b54995fdc99f9934c847a87125e4f5 Mon Sep 17 00:00:00 2001 From: Alberto Garcia Date: Fri, 10 Jul 2020 18:12:57 +0200 Subject: [PATCH] qcow2: Add qcow2_get_subcluster_range_type() There are situations in which we want to know how many contiguous subclusters of the same type there are in a given cluster. This can be done by simply iterating over the subclusters and repeatedly calling qcow2_get_subcluster_type() for each one of them. However once we determined the type of a subcluster we can check the rest efficiently by counting the number of adjacent ones (or zeroes) in the bitmap. This is what this function does. Signed-off-by: Alberto Garcia Reviewed-by: Eric Blake Reviewed-by: Max Reitz Message-Id: Signed-off-by: Max Reitz --- block/qcow2-cluster.c | 51 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 0b762502f6..2fe7a0f79c 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -375,6 +375,57 @@ fail: return ret; } +/* + * For a given L2 entry, count the number of contiguous subclusters of + * the same type starting from @sc_from. Compressed clusters are + * treated as if they were divided into subclusters of size + * s->subcluster_size. + * + * Return the number of contiguous subclusters and set @type to the + * subcluster type. + * + * If the L2 entry is invalid return -errno and set @type to + * QCOW2_SUBCLUSTER_INVALID. + */ +G_GNUC_UNUSED +static int qcow2_get_subcluster_range_type(BlockDriverState *bs, + uint64_t l2_entry, + uint64_t l2_bitmap, + unsigned sc_from, + QCow2SubclusterType *type) +{ + BDRVQcow2State *s = bs->opaque; + uint32_t val; + + *type = qcow2_get_subcluster_type(bs, l2_entry, l2_bitmap, sc_from); + + if (*type == QCOW2_SUBCLUSTER_INVALID) { + return -EINVAL; + } else if (!has_subclusters(s) || *type == QCOW2_SUBCLUSTER_COMPRESSED) { + return s->subclusters_per_cluster - sc_from; + } + + switch (*type) { + case QCOW2_SUBCLUSTER_NORMAL: + val = l2_bitmap | QCOW_OFLAG_SUB_ALLOC_RANGE(0, sc_from); + return cto32(val) - sc_from; + + case QCOW2_SUBCLUSTER_ZERO_PLAIN: + case QCOW2_SUBCLUSTER_ZERO_ALLOC: + val = (l2_bitmap | QCOW_OFLAG_SUB_ZERO_RANGE(0, sc_from)) >> 32; + return cto32(val) - sc_from; + + case QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN: + case QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC: + val = ((l2_bitmap >> 32) | l2_bitmap) + & ~QCOW_OFLAG_SUB_ALLOC_RANGE(0, sc_from); + return ctz32(val) - sc_from; + + default: + g_assert_not_reached(); + } +} + /* * Checks how many clusters in a given L2 slice are contiguous in the image * file. As soon as one of the flags in the bitmask stop_flags changes compared