Btrfs: Combine per-page recover in dev-replace and scrub

The code are similar, combine them to make code clean and easy to maintenance.
Some lost condition are also completed with benefit of this combination.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/scrub.c

@@ -1107,54 +1107,10 @@ nodatasum_case:
 		}
 	}
 
-	/*
-	 * for dev_replace, pick good pages and write to the target device.
-	 */
-	if (sctx->is_dev_replace) {
-		success = 1;
-		for (page_num = 0; page_num < sblock_bad->page_count;
-		     page_num++) {
-			struct scrub_block *sblock_other = NULL;
-
-			for (mirror_index = 0;
-			     mirror_index < BTRFS_MAX_MIRRORS &&
-			     sblocks_for_recheck[mirror_index].page_count > 0;
-			     mirror_index++) {
-				if (!sblocks_for_recheck[mirror_index].
-				    pagev[page_num]->io_error) {
-					sblock_other = sblocks_for_recheck +
-						       mirror_index;
-					break;
-				}
-			}
-
-			if (!sblock_other) {
-				/*
-				 * did not find a mirror to fetch the page
-				 * from. scrub_write_page_to_dev_replace()
-				 * handles this case (page->io_error), by
-				 * filling the block with zeros before
-				 * submitting the write request
-				 */
-				sblock_other = sblock_bad;
-				success = 0;
-			}
-
-			if (scrub_write_page_to_dev_replace(sblock_other,
-							    page_num) != 0) {
-				btrfs_dev_replace_stats_inc(
-					&sctx->dev_root->
-					fs_info->dev_replace.
-					num_write_errors);
-				success = 0;
-			}
-		}
-
-		goto out;
-	}
+	if (sblock_bad->no_io_error_seen && !sctx->is_dev_replace)
+		goto did_not_correct_error;
 
 	/*
-	 * for regular scrub, repair those pages that are errored.
 	 * In case of I/O errors in the area that is supposed to be
 	 * repaired, continue by picking good copies of those pages.
 	 * Select the good pages from mirrors to rewrite bad pages from
@@ -1178,44 +1134,64 @@ nodatasum_case:
 	 * mirror, even if other 512 byte sectors in the same PAGE_SIZE
 	 * area are unreadable.
 	 */
-
-	/* can only fix I/O errors from here on */
-	if (sblock_bad->no_io_error_seen)
-		goto did_not_correct_error;
-
 	success = 1;
-	for (page_num = 0; page_num < sblock_bad->page_count; page_num++) {
+	for (page_num = 0; page_num < sblock_bad->page_count;
+	     page_num++) {
 		struct scrub_page *page_bad = sblock_bad->pagev[page_num];
+		struct scrub_block *sblock_other = NULL;
 
-		if (!page_bad->io_error)
+		/* skip no-io-error page in scrub */
+		if (!page_bad->io_error && !sctx->is_dev_replace)
 			continue;
 
-		for (mirror_index = 0;
-		     mirror_index < BTRFS_MAX_MIRRORS &&
-		     sblocks_for_recheck[mirror_index].page_count > 0;
-		     mirror_index++) {
-			struct scrub_block *sblock_other = sblocks_for_recheck +
-							   mirror_index;
-			struct scrub_page *page_other = sblock_other->pagev[
-							page_num];
-
-			if (!page_other->io_error) {
-				ret = scrub_repair_page_from_good_copy(
-					sblock_bad, sblock_other, page_num, 0);
-				if (0 == ret) {
-					page_bad->io_error = 0;
-					break; /* succeeded for this page */
+		/* try to find no-io-error page in mirrors */
+		if (page_bad->io_error) {
+			for (mirror_index = 0;
+			     mirror_index < BTRFS_MAX_MIRRORS &&
+			     sblocks_for_recheck[mirror_index].page_count > 0;
+			     mirror_index++) {
+				if (!sblocks_for_recheck[mirror_index].
+				    pagev[page_num]->io_error) {
+					sblock_other = sblocks_for_recheck +
+						       mirror_index;
+					break;
 				}
 			}
+			if (!sblock_other)
+				success = 0;
 		}
 
-		if (page_bad->io_error) {
-			/* did not find a mirror to copy the page from */
-			success = 0;
+		if (sctx->is_dev_replace) {
+			/*
+			 * did not find a mirror to fetch the page
+			 * from. scrub_write_page_to_dev_replace()
+			 * handles this case (page->io_error), by
+			 * filling the block with zeros before
+			 * submitting the write request
+			 */
+			if (!sblock_other)
+				sblock_other = sblock_bad;
+
+			if (scrub_write_page_to_dev_replace(sblock_other,
+							    page_num) != 0) {
+				btrfs_dev_replace_stats_inc(
+					&sctx->dev_root->
+					fs_info->dev_replace.
+					num_write_errors);
+				success = 0;
+			}
+		} else if (sblock_other) {
+			ret = scrub_repair_page_from_good_copy(sblock_bad,
+							       sblock_other,
+							       page_num, 0);
+			if (0 == ret)
+				page_bad->io_error = 0;
+			else
+				success = 0;
 		}
 	}
 
-	if (success) {
+	if (success && !sctx->is_dev_replace) {
 		if (is_metadata || have_csum) {
 			/*
 			 * need to verify the checksum now that all