criu: pagemap: introduce advance() helper for pagemap iteration

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/pagemap.c

@@ -137,26 +137,30 @@ int dedup_one_iovec(struct page_read *pr, struct iovec *iov)
 	return 0;
 }
 
-static int get_pagemap(struct page_read *pr, struct iovec *iov)
+static int advance(struct page_read *pr)
 {
-	PagemapEntry *pe;
-
 	pr->curr_pme++;
 	if (pr->curr_pme >= pr->nr_pmes)
 		return 0;
 
-	pe = pr->pmes[pr->curr_pme];
+	pr->pe = pr->pmes[pr->curr_pme];
+	pr->cvaddr = pr->pe->vaddr;
 
-	pagemap2iovec(pe, iov);
+	return 1;
+}
 
-	pr->pe = pe;
-	pr->cvaddr = (unsigned long)iov->iov_base;
+static int get_pagemap(struct page_read *pr, struct iovec *iov)
+{
+	if (!advance(pr))
+		return 0;
 
-	if (pe->in_parent && !pr->parent) {
+	if (pr->pe->in_parent && !pr->parent) {
 		pr_err("No parent for snapshot pagemap\n");
 		return -1;
 	}
 
+	pagemap2iovec(pr->pe, iov);
+
 	return 1;
 }
 
@@ -172,35 +176,23 @@ static void skip_pagemap_pages(struct page_read *pr, unsigned long len)
 
 static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr)
 {
-	int ret;
-	struct iovec iov;
-
-	if (pr->pe)
-		pagemap2iovec(pr->pe, &iov);
-	else
-		goto new_pagemap;
-
-	while (1) {
-		unsigned long iov_end;
-
-		if (vaddr < pr->cvaddr)
-			return 0;
+	pr->reset(pr);
 
-		iov_end = (unsigned long)iov.iov_base + iov.iov_len;
+	while (advance(pr)) {
+		unsigned long start = pr->pe->vaddr;
+		unsigned long len = pr->pe->nr_pages * PAGE_SIZE;
+		unsigned long end = start + len;
 
-		if (iov_end <= vaddr) {
-			skip_pagemap_pages(pr, iov_end - pr->cvaddr);
-new_pagemap:
-			ret = get_pagemap(pr, &iov);
-			if (ret <= 0)
-				return ret;
-
-			continue;
+		if (vaddr >= start && vaddr < end) {
+			skip_pagemap_pages(pr, vaddr - pr->cvaddr);
+			return 1;
 		}
 
-		skip_pagemap_pages(pr, vaddr - pr->cvaddr);
-		return 1;
+		if (end <= vaddr)
+			skip_pagemap_pages(pr, end - pr->cvaddr);
 	}
+
+	return 0;
 }
 
 static inline void pagemap_bound_check(PagemapEntry *pe, unsigned long vaddr, int nr)