On 3/17/20 1:16 PM, Alberto Garcia wrote:
The L2 bitmap needs to be updated after each write to indicate what new subclusters are now allocated.This needs to happen even if the cluster was already allocated and the L2 entry was otherwise valid. Signed-off-by: Alberto Garcia <be...@igalia.com> Reviewed-by: Max Reitz <mre...@redhat.com> --- block/qcow2-cluster.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index ceacd91ea3..dfd8b66958 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1006,6 +1006,23 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m) assert((offset & L2E_OFFSET_MASK) == offset);set_l2_entry(s, l2_slice, l2_index + i, offset | QCOW_OFLAG_COPIED);+ + /* Update bitmap with the subclusters that were just written */ + if (has_subclusters(s)) { + unsigned written_from = m->cow_start.offset; + unsigned written_to = m->cow_end.offset + m->cow_end.nb_bytes ?: + m->nb_clusters << s->cluster_bits; + uint64_t l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i); + int sc; + for (sc = 0; sc < s->subclusters_per_cluster; sc++) { + int sc_off = i * s->cluster_size + sc * s->subcluster_size; + if (sc_off >= written_from && sc_off < written_to) { + l2_bitmap |= QCOW_OFLAG_SUB_ALLOC(sc); + l2_bitmap &= ~QCOW_OFLAG_SUB_ZERO(sc); + } + }
Are there more efficient ways to set this series of bits than iterating one bit at a time, while still remaining legible? For example, what if we had something like:
l2_bitmap = get_l2_bitmap(...); int sc_from = OFFSET_TO_SC(written_from); int sc_to = OFFSET_TO_SC(written_to - 1); l2_bitmap |= QCOW_OFLAG_SUB_ALLOC_RANGE(sc_from, sc_to); l2_bitmap &= ~QCOW_OFLAG_SUB_ZERO_RANGE(sc_from, sc_to); which would require macros: #define OFFSET_TO_SC(offset) (offset >> (s->cluster_bits - 6)) #define QCOW_OFLAG_SUB_ALLOC_RANGE(from, to) \ deposit64(0, (from), (len) - (from), -1) #define QCOW_OFLAG_SUB_ZERO_RANGE(from, to) \ deposit64(0, (from) + 32, (len) - (from) + 32, -1)
+ set_l2_bitmap(s, l2_slice, l2_index + i, l2_bitmap);
I'm hoping this function doesn't cause redundant I/O if the L2 entry didn't actually change. But that's not the concern for this patch.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
