[PoC PATCH 08/11] btrfs: scrub: use dedicated super block verification function to scrub one super block

[Qu Wenruo <wqu@suse.com>]

There is really no need to go through the super complex scrub_sectors()
to just handle super blocks.

This patch will introduce a dedicated function (less than 50 lines) to
handle super block scrubing.

This new function will introduce a behavior change, instead of using the
complex but concurrent scrub_bio system, here we just go
submit-and-wait.

There is really not much sense to care the performance of super block
scrubbing. It only has 3 super blocks at most, and they are all scattered
around the devices already.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 43 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 162f7e1dd378..9a9e706cba3e 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -5239,6 +5239,38 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 	return ret;
 }
 
+static int scrub2_one_super(struct scrub_ctx *sctx,
+			    struct btrfs_device *scrub_dev,
+			    struct page *page, u64 physical, u64 generation)
+{
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct bio_vec bvec;
+	struct bio bio;
+	struct btrfs_super_block *sb = page_address(page);
+	int ret;
+
+	bio_init(&bio, scrub_dev->bdev, &bvec, 1, REQ_OP_READ);
+	bio_add_page(&bio, page, BTRFS_SUPER_INFO_SIZE, 0);
+	ret = submit_bio_wait(&bio);
+	bio_uninit(&bio);
+
+	if (ret < 0)
+		return ret;
+	ret = btrfs_check_super_csum(fs_info, sb);
+	if (ret < 0)
+		return ret;
+	if (btrfs_super_generation(sb) != generation) {
+		btrfs_err_rl(fs_info,
+"super block at physical %llu devid %llu has bad generation, has %llu expect %llu",
+			     physical, scrub_dev->devid,
+			     btrfs_super_generation(sb), generation);
+		return -EUCLEAN;
+	}
+
+	ret = btrfs_validate_super(fs_info, sb, -1);
+	return ret;
+}
+
 static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
 					   struct btrfs_device *scrub_dev)
 {
@@ -5246,11 +5278,16 @@ static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
 	u64	bytenr;
 	u64	gen;
 	int	ret;
+	struct page *page;
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
 
 	if (BTRFS_FS_ERROR(fs_info))
 		return -EROFS;
 
+	page = alloc_page(GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+
 	/* Seed devices of a new filesystem has their own generation. */
 	if (scrub_dev->fs_devices != fs_info->fs_devices)
 		gen = scrub_dev->generation;
@@ -5265,13 +5302,11 @@ static noinline_for_stack int scrub_supers(struct scrub_ctx *sctx,
 		if (!btrfs_check_super_location(scrub_dev, bytenr))
 			continue;
 
-		ret = scrub_sectors(sctx, bytenr, BTRFS_SUPER_INFO_SIZE, bytenr,
-				    scrub_dev, BTRFS_EXTENT_FLAG_SUPER, gen, i,
-				    NULL, bytenr);
+		ret = scrub2_one_super(sctx, scrub_dev, page, bytenr, gen);
 		if (ret)
 			return ret;
 	}
-	wait_event(sctx->list_wait, atomic_read(&sctx->bios_in_flight) == 0);
+	__free_page(page);
 
 	return 0;
 }
-- 
2.38.1