[PATCH PoC v2 10/10] btrfs: scrub: implement the repair (writeback) functionality

[Qu Wenruo <wqu@suse.com>]

This adds the repair functionality for scrub_fs.

Since previous patch has implemented the final verification part, all
sectors that can be repaired will have SCRUB_FS_SECTOR_FLAG_RECOVERABLE,
we just need to submit write bios for them.

And just like the old scrub interface, we don't report writeback error.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 89735ff6143a..27d96778206c 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -5362,6 +5362,93 @@ static void scrub_fs_update_veritical(struct scrub_fs_ctx *sfctx,
 	}
 }
 
+static void scrub_fs_write_endio(struct bio *bio)
+{
+	struct scrub_fs_ctx *sfctx = bio->bi_private;
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+	unsigned int bio_size = 0;
+
+	bio_for_each_segment_all(bvec, bio, iter_all)
+		bio_size += bvec->bv_len;
+
+	/* Repair should be inside one stripe. */
+	ASSERT(bio_size <= BTRFS_STRIPE_LEN);
+
+	atomic_dec(&sfctx->bios_under_io);
+	wake_up(&sfctx->wait);
+	bio_put(bio);
+}
+
+static void scrub_fs_repair_mirror(struct scrub_fs_ctx *sfctx,
+				   struct btrfs_io_context *bioc, int mirror_nr)
+{
+	struct bio *bio = NULL;
+	int last_sector = -1;
+	int i;
+
+	ASSERT(mirror_nr < bioc->num_stripes);
+
+	for (i = 0; i < sfctx->sectors_per_stripe; i++) {
+		struct scrub_fs_sector *sector =
+			scrub_fs_get_sector(sfctx, i, mirror_nr);
+
+		if (sector->flags & SCRUB_FS_SECTOR_FLAG_DEV_MISSING ||
+		    sector->flags & SCRUB_FS_SECTOR_FLAG_GOOD ||
+		    !(sector->flags & SCRUB_FS_SECTOR_FLAG_RECOVERABLE))
+			continue;
+
+		/* No bio allocated, alloc a new one. */
+		if (!bio) {
+			blk_opf_t opf = REQ_OP_WRITE | REQ_BACKGROUND;
+
+			if (sector->flags & SCRUB_FS_SECTOR_FLAG_META)
+				opf |= REQ_META;
+
+			bio = bio_alloc(bioc->stripes[mirror_nr].dev->bdev,
+					sfctx->sectors_per_stripe, opf,
+					GFP_KERNEL);
+			/* It's backed up by mempool. */
+			ASSERT(bio);
+
+			bio->bi_iter.bi_sector =
+				(bioc->stripes[mirror_nr].physical +
+				 (i << sfctx->fs_info->sectorsize_bits)) >>
+				SECTOR_SHIFT;
+			bio->bi_private = sfctx;
+			bio->bi_end_io = scrub_fs_write_endio;
+
+			last_sector = i - 1;
+		}
+
+		/* Can merge into preivous bio.*/
+		if (last_sector == i - 1) {
+			struct page *page =
+				scrub_fs_get_page(sfctx, i, mirror_nr);
+			unsigned int page_off =
+				scrub_fs_get_page_offset(sfctx, i, mirror_nr);
+			int ret;
+
+			ret = bio_add_page(bio, page, sfctx->fs_info->sectorsize,
+					   page_off);
+			ASSERT(ret == sfctx->fs_info->sectorsize);
+			last_sector = i;
+			continue;
+		}
+
+		/* Can not merge, has to submit the current one and retry. */
+		ASSERT(bio);
+		atomic_inc(&sfctx->bios_under_io);
+		submit_bio(bio);
+		bio = NULL;
+		i--;
+	}
+	if (bio) {
+		atomic_inc(&sfctx->bios_under_io);
+		submit_bio(bio);
+	}
+}
+
 static int scrub_fs_one_stripe(struct scrub_fs_ctx *sfctx)
 {
 	struct btrfs_fs_info *fs_info = sfctx->fs_info;
@@ -5413,7 +5500,14 @@ static int scrub_fs_one_stripe(struct scrub_fs_ctx *sfctx)
 	for (i = 0; i < sfctx->sectors_per_stripe; i++)
 		scrub_fs_update_veritical(sfctx, i);
 
-	/* Place holder for repair write-back code */
+	/* Submit repair*/
+	if (!sfctx->readonly) {
+		for (i = 0; i < sfctx->nr_copies; i++)
+			scrub_fs_repair_mirror(sfctx, bioc, i);
+		wait_event(sfctx->wait, atomic_read(&sfctx->bios_under_io) == 0);
+	}
+	ASSERT(atomic_read(&sfctx->bios_under_io) == 0);
+
 out:
 	btrfs_put_bioc(bioc);
 	btrfs_bio_counter_dec(fs_info);
-- 
2.37.3