[RFC PATCH 03/10] btrfs: allow remapped chunks to have zero stripes

[Mark Harmstone <maharmstone@fb.com>]

When a chunk has been fully remapped, we are going to set its
num_stripes to 0, as it will no longer represent a physical location on
disk.

Change tree-checker to allow for this, and fix a couple of
divide-by-zeroes seen elsewhere.

Signed-off-by: Mark Harmstone <maharmstone@fb.com>
---
 fs/btrfs/tree-checker.c | 16 +++++++++-------
 fs/btrfs/volumes.c      |  8 +++++++-
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 0505f8d76581..fd83df06e3fb 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -829,7 +829,7 @@ int btrfs_check_chunk_valid(const struct btrfs_fs_info *fs_info,
 	u64 type;
 	u64 features;
 	u32 chunk_sector_size;
-	bool mixed = false;
+	bool mixed = false, remapped;
 	int raid_index;
 	int nparity;
 	int ncopies;
@@ -853,12 +853,14 @@ int btrfs_check_chunk_valid(const struct btrfs_fs_info *fs_info,
 	ncopies = btrfs_raid_array[raid_index].ncopies;
 	nparity = btrfs_raid_array[raid_index].nparity;
 
-	if (unlikely(!num_stripes)) {
+	remapped = type & BTRFS_BLOCK_GROUP_REMAPPED;
+
+	if (unlikely(!remapped && !num_stripes)) {
 		chunk_err(fs_info, leaf, chunk, logical,
 			  "invalid chunk num_stripes, have %u", num_stripes);
 		return -EUCLEAN;
 	}
-	if (unlikely(num_stripes < ncopies)) {
+	if (unlikely(!remapped && num_stripes < ncopies)) {
 		chunk_err(fs_info, leaf, chunk, logical,
 			  "invalid chunk num_stripes < ncopies, have %u < %d",
 			  num_stripes, ncopies);
@@ -960,7 +962,7 @@ int btrfs_check_chunk_valid(const struct btrfs_fs_info *fs_info,
 		}
 	}
 
-	if (unlikely((type & BTRFS_BLOCK_GROUP_RAID10 &&
+	if (unlikely(!remapped && ((type & BTRFS_BLOCK_GROUP_RAID10 &&
 		      sub_stripes != btrfs_raid_array[BTRFS_RAID_RAID10].sub_stripes) ||
 		     (type & BTRFS_BLOCK_GROUP_RAID1 &&
 		      num_stripes != btrfs_raid_array[BTRFS_RAID_RAID1].devs_min) ||
@@ -975,7 +977,7 @@ int btrfs_check_chunk_valid(const struct btrfs_fs_info *fs_info,
 		     (type & BTRFS_BLOCK_GROUP_DUP &&
 		      num_stripes != btrfs_raid_array[BTRFS_RAID_DUP].dev_stripes) ||
 		     ((type & BTRFS_BLOCK_GROUP_PROFILE_MASK) == 0 &&
-		      num_stripes != btrfs_raid_array[BTRFS_RAID_SINGLE].dev_stripes))) {
+		      num_stripes != btrfs_raid_array[BTRFS_RAID_SINGLE].dev_stripes)))) {
 		chunk_err(fs_info, leaf, chunk, logical,
 			"invalid num_stripes:sub_stripes %u:%u for profile %llu",
 			num_stripes, sub_stripes,
@@ -999,11 +1001,11 @@ static int check_leaf_chunk_item(struct extent_buffer *leaf,
 	struct btrfs_fs_info *fs_info = leaf->fs_info;
 	int num_stripes;
 
-	if (unlikely(btrfs_item_size(leaf, slot) < sizeof(struct btrfs_chunk))) {
+	if (unlikely(btrfs_item_size(leaf, slot) < offsetof(struct btrfs_chunk, stripe))) {
 		chunk_err(fs_info, leaf, chunk, key->offset,
 			"invalid chunk item size: have %u expect [%zu, %u)",
 			btrfs_item_size(leaf, slot),
-			sizeof(struct btrfs_chunk),
+			offsetof(struct btrfs_chunk, stripe),
 			BTRFS_LEAF_DATA_SIZE(fs_info));
 		return -EUCLEAN;
 	}
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 0698613276d9..77194bb46b40 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6133,6 +6133,12 @@ struct btrfs_discard_stripe *btrfs_map_discard(struct btrfs_fs_info *fs_info,
 		goto out_free_map;
 	}
 
+	/* avoid divide by zero on fully-remapped chunks */
+	if (map->num_stripes == 0) {
+		ret = -EOPNOTSUPP;
+		goto out_free_map;
+	}
+
 	offset = logical - map->start;
 	length = min_t(u64, map->start + map->chunk_len - logical, length);
 	*length_ret = length;
@@ -6953,7 +6959,7 @@ u64 btrfs_calc_stripe_length(const struct btrfs_chunk_map *map)
 {
 	const int data_stripes = calc_data_stripes(map->type, map->num_stripes);
 
-	return div_u64(map->chunk_len, data_stripes);
+	return data_stripes ? div_u64(map->chunk_len, data_stripes) : 0;
 }
 
 #if BITS_PER_LONG == 32
-- 
2.49.0