[sheepdog] [PATCH 06/10] sheep: decrement generational reference count on copy-on-write
MORITA Kazutaka
morita.kazutaka at gmail.com
Tue May 21 02:11:55 CEST 2013
From: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
This decrements a reference count of the old data object when
allocating a new data object on CoW.
Signed-off-by: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
---
sheep/gateway.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 102 insertions(+), 1 deletion(-)
diff --git a/sheep/gateway.c b/sheep/gateway.c
index 506cea5..fb7ed21 100644
--- a/sheep/gateway.c
+++ b/sheep/gateway.c
@@ -317,9 +317,88 @@ static int gateway_forward_request(struct request *req)
return err_ret;
}
+static int prepare_obj_refcnt(const struct sd_req *hdr, uint32_t *vids,
+ struct generation_reference *refs)
+{
+ int ret;
+ size_t nr_vids = hdr->data_length / sizeof(*vids);
+ uint64_t offset;
+ int start;
+
+ offset = hdr->obj.offset - offsetof(struct sd_inode, data_vdi_id);
+ start = offset / sizeof(*vids);
+
+ ret = read_object(hdr->obj.oid, (char *)vids, nr_vids * sizeof(vids[0]),
+ offsetof(struct sd_inode, data_vdi_id[start]));
+ if (ret != SD_RES_SUCCESS) {
+ sd_eprintf("failed to read vdi, %" PRIx64, hdr->obj.oid);
+ return ret;
+ }
+ ret = read_object(hdr->obj.oid, (char *)refs, nr_vids * sizeof(refs[0]),
+ offsetof(struct sd_inode, data_ref[start]));
+ if (ret != SD_RES_SUCCESS) {
+ sd_eprintf("failed to read vdi, %" PRIx64, hdr->obj.oid);
+ return ret;
+ }
+
+ return ret;
+}
+
+/*
+ * This function decreases a refcnt of vid_to_data_oid(old_vid, idx) and
+ * increases one of vid_to_data_oid(new_vid, idx)
+ */
+static int update_obj_refcnt(const struct sd_req *hdr, uint32_t *vids,
+ uint32_t *new_vids,
+ struct generation_reference *refs)
+{
+ int i, start, ret = SD_RES_SUCCESS;
+ size_t nr_vids = hdr->data_length / sizeof(*vids);
+ uint64_t offset;
+
+ offset = hdr->obj.offset - offsetof(struct sd_inode, data_vdi_id);
+ start = offset / sizeof(*vids);
+
+ for (i = 0; i < nr_vids; i++) {
+ if (vids[i] == 0 || vids[i] == new_vids[i])
+ continue;
+
+ ret = dec_object_refcnt(vid_to_data_oid(vids[i], i + start),
+ refs[i].generation, refs[i].count);
+ if (ret != SD_RES_SUCCESS)
+ sd_eprintf("fail, %d", ret);
+
+ refs[i].generation = 0;
+ refs[i].count = 0;
+ }
+
+ return write_object(hdr->obj.oid, (char *)refs, nr_vids * sizeof(*refs),
+ offsetof(struct sd_inode,
+ data_ref) + start * sizeof(*refs),
+ false);
+}
+
+/*
+ * return true if the request updates a data_vdi_id field of a vdi object
+ *
+ * XXX: we assume that VMs don't update the inode header and the data_vdi_id
+ * field at the same time.
+ */
+static bool is_data_vid_update(const struct sd_req *hdr)
+{
+ return is_vdi_obj(hdr->obj.oid) &&
+ SD_INODE_HEADER_SIZE <= hdr->obj.offset &&
+ hdr->obj.offset + hdr->data_length <=
+ offsetof(struct sd_inode, data_ref);
+}
+
int gateway_write_obj(struct request *req)
{
uint64_t oid = req->rq.obj.oid;
+ int ret;
+ struct sd_req *hdr = &req->rq;
+ uint32_t *vids = NULL, *new_vids = req->data;
+ struct generation_reference *refs = NULL;
if (oid_is_readonly(oid))
return SD_RES_READONLY;
@@ -327,7 +406,29 @@ int gateway_write_obj(struct request *req)
if (!bypass_object_cache(req))
return object_cache_handle_request(req);
- return gateway_forward_request(req);
+ if (is_data_vid_update(hdr)) {
+ size_t nr_vids = hdr->data_length / sizeof(*vids);
+
+ /* read the previous vids to discard their references later */
+ vids = xzalloc(sizeof(*vids) * nr_vids);
+ refs = xzalloc(sizeof(*refs) * nr_vids);
+ ret = prepare_obj_refcnt(hdr, vids, refs);
+ if (ret != SD_RES_SUCCESS)
+ goto out;
+ }
+
+ ret = gateway_forward_request(req);
+ if (ret != SD_RES_SUCCESS)
+ goto out;
+
+ if (is_data_vid_update(hdr)) {
+ sd_dprintf("udpate reference counts, %" PRIx64, hdr->obj.oid);
+ ret = update_obj_refcnt(hdr, vids, new_vids, refs);
+ }
+out:
+ free(vids);
+ free(refs);
+ return ret;
}
int gateway_create_and_write_obj(struct request *req)
--
1.7.9.5
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