deduplication: make it recursively deduplicate all parent snapshots

If we write a page into image and punch it from parnet, checking
only one level down is not enough -- the iovec can reside deeper.

That said, make the hole punching be recursive.
Signed-off-by: Tikhomirov Pavel <snorcht@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dedup.c

@@ -113,6 +113,9 @@ int dedup_one_iovec(struct page_read *pr, struct iovec *iov)
 		int ret;
 		struct iovec piov;
 		unsigned long  piov_end;
+		struct iovec tiov;
+		struct page_read * prp;
+
 		ret = seek_pagemap_page(pr, off, false);
 		if (ret == -1)
 			return -1;
@@ -138,6 +141,16 @@ int dedup_one_iovec(struct page_read *pr, struct iovec *iov)
 				return -1;
 			}
 		}
+		prp = pr->parent;
+		if (prp) {
+			/* recursively */
+			pr_debug("Go to next parent level");
+			tiov.iov_base = (void*)off;
+			tiov.iov_len = min(piov_end, iov_end) - off;
+			ret = dedup_one_iovec(prp, &tiov);
+			if (ret != 0)
+				return -1;
+		}
 
 		if (piov_end < iov_end) {
 			off = piov_end;