page-server: Merge async and sync read API calls

Now these two look exactly the same and we can have
only one call with additional sync/async (flags) arg.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/page-xfer.h

@@ -57,9 +57,7 @@ extern int check_parent_page_xfer(int fd_type, long id);
 extern int request_remote_pages(int pid, unsigned long addr, int nr_pages);
 
 typedef int (*ps_async_read_complete)(int pid, unsigned long vaddr, int nr_pages, void *);
-extern int page_server_start_async_read(void *buf, int nr_pages,
-		ps_async_read_complete complete, void *priv);
-extern int page_server_start_sync_read(void *buf, int nr_pages,
-		ps_async_read_complete complete, void *priv);
+extern int page_server_start_read(void *buf, int nr_pages,
+		ps_async_read_complete complete, void *priv, unsigned flags);
 
 #endif /* __CR_PAGE_XFER__H__ */

criu/page-xfer.c

@@ -1069,7 +1069,7 @@ struct ps_async_read {
 
 static LIST_HEAD(async_reads);
 
-int page_server_start_async_read(void *buf, int nr_pages,
+static int page_server_start_async_read(void *buf, int nr_pages,
 		ps_async_read_complete complete, void *priv)
 {
 	struct ps_async_read *ar;
@@ -1201,7 +1201,7 @@ static int receive_remote_pages(int len, void *buf)
 	return 0;
 }
 
-int page_server_start_sync_read(void *buf, int nr,
+static int page_server_start_sync_read(void *buf, int nr,
 		ps_async_read_complete complete, void *priv)
 {
 	int ret, pid, new_nr;
@@ -1223,3 +1223,12 @@ int page_server_start_sync_read(void *buf, int nr,
 
 	return ret;
 }
+
+int page_server_start_read(void *buf, int nr,
+		ps_async_read_complete complete, void *priv, unsigned flags)
+{
+	if (flags & PR_ASYNC)
+		return page_server_start_async_read(buf, nr, complete, priv);
+	else
+		return page_server_start_sync_read(buf, nr, complete, priv);
+}

criu/pagemap.c

@@ -438,12 +438,10 @@ static int maybe_read_page_remote(struct page_read *pr, unsigned long vaddr,
 
 	/* We always do PR_ASAP mode here (FIXME?) */
 	ret = request_remote_pages(pr->pid, vaddr, nr);
-	if (ret < 0)
-		return ret;
-	if (flags & PR_ASYNC)
-		return page_server_start_async_read(buf, nr, read_page_complete, pr);
-	else
-		return page_server_start_sync_read(buf, nr, read_page_complete, pr);
+	if (!ret)
+		ret = page_server_start_read(buf, nr,
+				read_page_complete, pr, flags);
+	return ret;
 }
 
 static int read_pagemap_page(struct page_read *pr, unsigned long vaddr, int nr,