pagemap: replace seek_page with seek_pagemap method

The only external users of ->seek_page method are page-xfer and uffd and
both of them are anyway interested in the entire pagemap rather than a
particular page.
The added 'skip_zero' parameter allows proper detection of zero pagemaps by
uffd.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/pagemap.h

@@ -53,8 +53,8 @@ struct page_read {
 	/* Advance page_read to the next entry (including zero pagemaps) */
 	int (*advance)(struct page_read *pr);
 	void (*close)(struct page_read *);
-	int (*seek_page)(struct page_read *pr, unsigned long vaddr);
 	int (*sync)(struct page_read *pr);
+	int (*seek_pagemap)(struct page_read *pr, unsigned long vaddr);
 
 	/* Private data of reader */
 	struct cr_img *pmi;

criu/page-xfer.c

@@ -202,7 +202,7 @@ static int check_pagehole_in_parent(struct page_read *p, struct iovec *iov)
 		struct iovec piov;
 		unsigned long pend;
 
-		ret = p->seek_page(p, off);
+		ret = p->seek_pagemap(p, off);
 		if (ret <= 0 || !p->pe) {
 			pr_err("Missing %lx in parent pagemap\n", off);
 			return -1;

criu/pagemap.c

@@ -82,6 +82,8 @@ static int punch_hole(struct page_read *pr, unsigned long off,
 	return 0;
 }
 
+static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr);
+
 int dedup_one_iovec(struct page_read *pr, struct iovec *iov)
 {
 	unsigned long off;
@@ -96,7 +98,7 @@ int dedup_one_iovec(struct page_read *pr, struct iovec *iov)
 		struct iovec tiov;
 		struct page_read * prp;
 
-		ret = pr->seek_page(pr, off);
+		ret = seek_pagemap_page(pr, off);
 		if (ret == 0) {
 			pr_warn("Missing %lx in parent pagemap\n", off);
 			if (off < pr->cvaddr && pr->cvaddr < iov_end)
@@ -172,7 +174,7 @@ static void skip_pagemap_pages(struct page_read *pr, unsigned long len)
 	pr->cvaddr += len;
 }
 
-static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr)
+static int seek_pagemap(struct page_read *pr, unsigned long vaddr)
 {
 	if (!pr->pe)
 		advance(pr);
@@ -186,7 +188,7 @@ static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr)
 			break;
 
 		if (vaddr >= start && vaddr < end) {
-			skip_pagemap_pages(pr, vaddr - pr->cvaddr);
+			skip_pagemap_pages(pr, start - pr->cvaddr);
 			return 1;
 		}
 
@@ -197,6 +199,16 @@ static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr)
 	return 0;
 }
 
+static int seek_pagemap_page(struct page_read *pr, unsigned long vaddr)
+{
+	if (seek_pagemap(pr, vaddr)) {
+		skip_pagemap_pages(pr, vaddr - pr->cvaddr);
+		return 1;
+	}
+
+	return 0;
+}
+
 static inline void pagemap_bound_check(PagemapEntry *pe, unsigned long vaddr, int nr)
 {
 	if (vaddr < pe->vaddr || (vaddr - pe->vaddr) / PAGE_SIZE + nr > pe->nr_pages) {
@@ -620,8 +632,8 @@ int open_page_read_at(int dfd, int pid, struct page_read *pr, int pr_flags)
 	pr->read_pages = read_pagemap_page;
 	pr->advance = advance;
 	pr->close = close_page_read;
-	pr->seek_page = seek_pagemap_page;
 	pr->sync = process_async_reads;
+	pr->seek_pagemap = seek_pagemap;
 	pr->id = ids++;
 
 	pr_debug("Opened page read %u (parent %u)\n",