page-read: introduce dup_page_read

The dup_page_read performs a shallow copy of a page_read object. It is
required for implementation of fork event in lazy-pages daemon.
When a restored process fork()'s a child, the lazy-pages daemon will handle
page faults of the child process, and it will use the parent process memory
dump for that.

travis-ci: success for lazy-pages: add non-#PF events handling (rev2)
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/pagemap.h

@@ -112,6 +112,13 @@ int pagemap_enqueue_iovec(struct page_read *pr, void *buf,
 			      unsigned long len, struct list_head *to);
 int pagemap_render_iovec(struct list_head *from, struct task_restore_args *ta);
 
+/*
+ * Create a shallow copy of page_read object.
+ * The new object shares the pagemap structures with the original, but
+ * maintains its own set of references to those structures.
+ */
+extern void dup_page_read(struct page_read *src, struct page_read *dst);
+
 extern int dedup_one_iovec(struct page_read *pr, unsigned long base,
 			   unsigned long len);
 

criu/pagemap.c

@@ -819,3 +819,16 @@ int open_page_read(int pid, struct page_read *pr, int pr_flags)
 {
 	return open_page_read_at(get_service_fd(IMG_FD_OFF), pid, pr, pr_flags);
 }
+
+
+#define DUP_IDS_BASE 1000
+
+void dup_page_read(struct page_read *src, struct page_read *dst)
+{
+	static int dup_ids = 1;
+
+	memcpy(dst, src, sizeof(*dst));
+	INIT_LIST_HEAD(&dst->async);
+	dst->id = src->id + DUP_IDS_BASE * dup_ids++;
+	dst->reset(dst);
+}