bcachefs: Erasure coding fixes & refactoring

 - Originally bch_extent_stripe_ptr didn't contain the block index,
   instead we'd have to search through the stripe pointers to figure out
   which pointer matched. When the block field was added to
   bch_extent_stripe_ptr, not all of the code was updated to use it.
   This patch fixes that, and we also now verify that field where it
   makes sense.

 - The ec_stripe_buf_init/exit() functions have been improved, and are
   now used by the bch2_ec_read_extent() (recovery read) path.

 - get_stripe_key() is now used by bch2_ec_read_extent().

 - We now have a getter and setter for checksums within a stripe, like
   we had previously for block sector counts, and ec_generate_checksums
   and ec_validate_checksums are now quite a bit smaller and cleaner.

ec.c still needs a lot of work, but this patch is slowly moving things
in the right direction.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/buckets.c

@@ -1656,7 +1656,7 @@ static int bch2_trans_mark_pointer(struct btree_trans *trans,
 }
 
 static int bch2_trans_mark_stripe_ptr(struct btree_trans *trans,
-			struct bch_extent_stripe_ptr p,
+			struct extent_ptr_decoded p,
 			s64 sectors, enum bch_data_type data_type)
 {
 	struct bch_fs *c = trans->c;
@@ -1666,14 +1666,22 @@ static int bch2_trans_mark_stripe_ptr(struct btree_trans *trans,
 	struct bch_replicas_padded r;
 	int ret = 0;
 
-	ret = trans_get_key(trans, BTREE_ID_EC, POS(0, p.idx), &iter, &k);
+	ret = trans_get_key(trans, BTREE_ID_EC, POS(0, p.ec.idx), &iter, &k);
 	if (ret < 0)
 		return ret;
 
 	if (k.k->type != KEY_TYPE_stripe) {
 		bch2_fs_inconsistent(c,
 			"pointer to nonexistent stripe %llu",
-			(u64) p.idx);
+			(u64) p.ec.idx);
+		ret = -EIO;
+		goto out;
+	}
+
+	if (!bch2_ptr_matches_stripe(bkey_s_c_to_stripe(k).v, p)) {
+		bch2_fs_inconsistent(c,
+			"stripe pointer doesn't match stripe %llu",
+			(u64) p.ec.idx);
 		ret = -EIO;
 		goto out;
 	}
@@ -1684,8 +1692,8 @@ static int bch2_trans_mark_stripe_ptr(struct btree_trans *trans,
 		goto out;
 
 	bkey_reassemble(&s->k_i, k);
-	stripe_blockcount_set(&s->v, p.block,
-		stripe_blockcount_get(&s->v, p.block) +
+	stripe_blockcount_set(&s->v, p.ec.block,
+		stripe_blockcount_get(&s->v, p.ec.block) +
 		sectors);
 	bch2_trans_update(trans, iter, &s->k_i, 0);
 
@@ -1736,7 +1744,7 @@ static int bch2_trans_mark_extent(struct btree_trans *trans,
 			dirty_sectors	       += disk_sectors;
 			r.e.devs[r.e.nr_devs++]	= p.ptr.dev;
 		} else {
-			ret = bch2_trans_mark_stripe_ptr(trans, p.ec,
+			ret = bch2_trans_mark_stripe_ptr(trans, p,
 					disk_sectors, data_type);
 			if (ret)
 				return ret;

fs/bcachefs/ec.h

@@ -60,9 +60,51 @@ static inline unsigned stripe_val_u64s(const struct bch_stripe *s)
 }
 
 static inline void *stripe_csum(struct bch_stripe *s,
-				unsigned dev, unsigned csum_idx)
+				unsigned block, unsigned csum_idx)
 {
-	return (void *) s + stripe_csum_offset(s, dev, csum_idx);
+	EBUG_ON(block >= s->nr_blocks);
+	EBUG_ON(csum_idx >= stripe_csums_per_device(s));
+
+	return (void *) s + stripe_csum_offset(s, block, csum_idx);
+}
+
+static inline struct bch_csum stripe_csum_get(struct bch_stripe *s,
+				   unsigned block, unsigned csum_idx)
+{
+	struct bch_csum csum = { 0 };
+
+	memcpy(&csum, stripe_csum(s, block, csum_idx), bch_crc_bytes[s->csum_type]);
+	return csum;
+}
+
+static inline void stripe_csum_set(struct bch_stripe *s,
+				   unsigned block, unsigned csum_idx,
+				   struct bch_csum csum)
+{
+	memcpy(stripe_csum(s, block, csum_idx), &csum, bch_crc_bytes[s->csum_type]);
+}
+
+static inline bool __bch2_ptr_matches_stripe(const struct bch_stripe *s,
+					     const struct bch_extent_ptr *ptr,
+					     unsigned block)
+{
+	unsigned nr_data = s->nr_blocks - s->nr_redundant;
+
+	if (block >= nr_data)
+		return false;
+
+	return  ptr->dev    == s->ptrs[block].dev &&
+		ptr->gen    == s->ptrs[block].gen &&
+		ptr->offset >= s->ptrs[block].offset &&
+		ptr->offset  < s->ptrs[block].offset + le16_to_cpu(s->sectors);
+}
+
+static inline bool bch2_ptr_matches_stripe(const struct bch_stripe *s,
+					   struct extent_ptr_decoded p)
+{
+	BUG_ON(!p.has_ec);
+
+	return __bch2_ptr_matches_stripe(s, &p.ptr, p.ec.block);
 }
 
 struct bch_read_bio;