libceph: add ceph_osdc_call() single-page helper

Add a convenience function to osd_client to send Ceph OSD
'class' ops. The interface assumes that the request and
reply data each consist of single pages.
Signed-off-by: Douglas Fuller <dfuller@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Alex Elder <elder@linaro.org>

include/linux/ceph/osd_client.h

@@ -397,6 +397,14 @@ extern void ceph_osdc_sync(struct ceph_osd_client *osdc);
 extern void ceph_osdc_flush_notifies(struct ceph_osd_client *osdc);
 void ceph_osdc_maybe_request_map(struct ceph_osd_client *osdc);
 
+int ceph_osdc_call(struct ceph_osd_client *osdc,
+		   struct ceph_object_id *oid,
+		   struct ceph_object_locator *oloc,
+		   const char *class, const char *method,
+		   unsigned int flags,
+		   struct page *req_page, size_t req_len,
+		   struct page *resp_page, size_t *resp_len);
+
 extern int ceph_osdc_readpages(struct ceph_osd_client *osdc,
 			       struct ceph_vino vino,
 			       struct ceph_file_layout *layout,

net/ceph/osd_client.c

@@ -4026,6 +4026,57 @@ void ceph_osdc_maybe_request_map(struct ceph_osd_client *osdc)
 }
 EXPORT_SYMBOL(ceph_osdc_maybe_request_map);
 
+/*
+ * Execute an OSD class method on an object.
+ *
+ * @flags: CEPH_OSD_FLAG_*
+ * @resp_len: out param for reply length
+ */
+int ceph_osdc_call(struct ceph_osd_client *osdc,
+		   struct ceph_object_id *oid,
+		   struct ceph_object_locator *oloc,
+		   const char *class, const char *method,
+		   unsigned int flags,
+		   struct page *req_page, size_t req_len,
+		   struct page *resp_page, size_t *resp_len)
+{
+	struct ceph_osd_request *req;
+	int ret;
+
+	req = ceph_osdc_alloc_request(osdc, NULL, 1, false, GFP_NOIO);
+	if (!req)
+		return -ENOMEM;
+
+	ceph_oid_copy(&req->r_base_oid, oid);
+	ceph_oloc_copy(&req->r_base_oloc, oloc);
+	req->r_flags = flags;
+
+	ret = ceph_osdc_alloc_messages(req, GFP_NOIO);
+	if (ret)
+		goto out_put_req;
+
+	osd_req_op_cls_init(req, 0, CEPH_OSD_OP_CALL, class, method);
+	if (req_page)
+		osd_req_op_cls_request_data_pages(req, 0, &req_page, req_len,
+						  0, false, false);
+	if (resp_page)
+		osd_req_op_cls_response_data_pages(req, 0, &resp_page,
+						   PAGE_SIZE, 0, false, false);
+
+	ceph_osdc_start_request(osdc, req, false);
+	ret = ceph_osdc_wait_request(osdc, req);
+	if (ret >= 0) {
+		ret = req->r_ops[0].rval;
+		if (resp_page)
+			*resp_len = req->r_ops[0].outdata_len;
+	}
+
+out_put_req:
+	ceph_osdc_put_request(req);
+	return ret;
+}
+EXPORT_SYMBOL(ceph_osdc_call);
+
 /*
  * init, shutdown
  */