criu: pagemap: add reset method

Rather than do open/close to reset pagemap, just update it's state.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/pagemap.h

@@ -52,6 +52,7 @@ struct page_read {
 	void (*skip_pages)(struct page_read *, unsigned long len);
 	int (*sync)(struct page_read *pr);
 	int (*seek_pagemap)(struct page_read *pr, unsigned long vaddr);
+	void (*reset)(struct page_read *pr);
 
 	/* Whether or not pages can be read in PIE code */
 	bool pieok;

criu/pagemap.c

@@ -547,6 +547,19 @@ static void close_page_read(struct page_read *pr)
 		free_pagemaps(pr);
 }
 
+static void reset_pagemap(struct page_read *pr)
+{
+	pr->cvaddr = 0;
+	pr->pi_off = 0;
+	pr->curr_pme = -1;
+	pr->pe = NULL;
+
+	/* FIXME: take care of bunch */
+
+	if (pr->parent)
+		reset_pagemap(pr->parent);
+}
+
 static int try_open_parent(int dfd, int pid, struct page_read *pr, int pr_flags)
 {
 	int pfd, ret;
@@ -701,6 +714,7 @@ int open_page_read_at(int dfd, int pid, struct page_read *pr, int pr_flags)
 	pr->skip_pages = skip_pagemap_pages;
 	pr->sync = process_async_reads;
 	pr->seek_pagemap = seek_pagemap;
+	pr->reset = reset_pagemap;
 	pr->id = ids++;
 	if (!pr->parent)
 		pr->pieok = true;