bcachefs: Unwritten extents support

- bch2_extent_merge checks unwritten bit
- read path returns 0s for unwritten extents without actually reading
- reflink path skips over unwritten extents
- bch2_bkey_ptrs_invalid() checks for extents with both written and
unwritten extents, and non-normal extents (stripes, btree ptrs) with
unwritten ptrs
- fiemap checks for unwritten extents and returns
FIEMAP_EXTENT_UNWRITTEN

Signed-off-by: Kent Overstreet <[e-mail]>

fs/bcachefs/bcachefs_format.h

···
 	__u64			type:1,
 				cached:1,
 				unused:1,
-				reservation:1,
+				unwritten:1,
 				offset:44, /* 8 petabytes */
 				dev:8,
 				gen:8;
···
 	__u64			gen:8,
 				dev:8,
 				offset:44,
-				reservation:1,
+				unwritten:1,
 				unused:1,
 				cached:1,
 				type:1;

fs/bcachefs/extents.c

···
 		return -EIO;
 
 	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
+		/*
+		 * Unwritten extent: no need to actually read, treat it as a
+		 * hole and return 0s:
+		 */
+		if (p.ptr.unwritten)
+			return 0;
+
 		ca = bch_dev_bkey_exists(c, p.ptr.dev);
 
 		/*
···
 		    rp.ptr.offset + rp.crc.offset ||
 		    lp.ptr.dev			!= rp.ptr.dev ||
 		    lp.ptr.gen			!= rp.ptr.gen ||
+		    lp.ptr.unwritten		!= rp.ptr.unwritten ||
 		    lp.has_ec			!= rp.has_ec)
 			return false;
 
···
 	const union bch_extent_entry *entry1, *entry2;
 	struct extent_ptr_decoded p1, p2;
 
+	if (bkey_extent_is_unwritten(k1) != bkey_extent_is_unwritten(k2))
+		return false;
+
 	bkey_for_each_ptr_decode(k1.k, ptrs1, p1, entry1)
 		bkey_for_each_ptr_decode(k2.k, ptrs2, p2, entry2)
 			if (p1.ptr.dev		== p2.ptr.dev &&
···
 				u32 offset;
 				u64 b = sector_to_bucket_and_offset(ca, ptr->offset, &offset);
 
-				prt_printf(out, "ptr: %u:%llu:%u gen %u%s", ptr->dev,
-				       b, offset, ptr->gen,
-				       ptr->cached ? " cached" : "");
-
+				prt_printf(out, "ptr: %u:%llu:%u gen %u",
+					   ptr->dev, b, offset, ptr->gen);
+				if (ptr->cached)
+					prt_str(out, " cached");
+				if (ptr->unwritten)
+					prt_str(out, " unwritten");
 				if (ca && ptr_stale(ca, ptr))
 					prt_printf(out, " stale");
 			}
···
 	unsigned size_ondisk = k.k->size;
 	unsigned nonce = UINT_MAX;
 	unsigned nr_ptrs = 0;
+	bool unwritten = false;
 	int ret;
 
 	if (bkey_is_btree_ptr(k.k))
···
 						 false, err);
 			if (ret)
 				return ret;
+
+			if (nr_ptrs && unwritten != entry->ptr.unwritten) {
+				prt_printf(err, "extent with unwritten and written ptrs");
+				return -BCH_ERR_invalid_bkey;
+			}
+
+			if (k.k->type != KEY_TYPE_extent && entry->ptr.unwritten) {
+				prt_printf(err, "has unwritten ptrs");
+				return -BCH_ERR_invalid_bkey;
+			}
+
+			unwritten = entry->ptr.unwritten;
 			nr_ptrs++;
 			break;
 		case BCH_EXTENT_ENTRY_crc32:

fs/bcachefs/extents.h

···
 	}
 }
 
+static inline bool bkey_extent_is_unwritten(struct bkey_s_c k)
+{
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	const struct bch_extent_ptr *ptr;
+
+	bkey_for_each_ptr(ptrs, ptr)
+		if (ptr->unwritten)
+			return true;
+	return false;
+}
+
+static inline bool bkey_extent_is_reservation(struct bkey_s_c k)
+{
+	return k.k->type == KEY_TYPE_reservation ||
+		bkey_extent_is_unwritten(k);
+}
+
 static inline struct bch_devs_list bch2_bkey_devs(struct bkey_s_c k)
 {
 	struct bch_devs_list ret = (struct bch_devs_list) { 0 };

fs/bcachefs/fs-io.c

···
 	return bch2_page_state(page) ?: __bch2_page_state_create(page, gfp);
 }
 
-static unsigned bkey_to_sector_state(const struct bkey *k)
+static unsigned bkey_to_sector_state(struct bkey_s_c k)
 {
-	if (k->type == KEY_TYPE_reservation)
+	if (bkey_extent_is_reservation(k))
 		return SECTOR_RESERVED;
-	if (bkey_extent_is_allocation(k))
+	if (bkey_extent_is_allocation(k.k))
 		return SECTOR_ALLOCATED;
 	return SECTOR_UNALLOCATED;
 }
···
 			   SPOS(inum.inum, offset, snapshot),
 			   BTREE_ITER_SLOTS, k, ret) {
 		unsigned nr_ptrs = bch2_bkey_nr_ptrs_fully_allocated(k);
-		unsigned state = bkey_to_sector_state(k.k);
+		unsigned state = bkey_to_sector_state(k);
 
 		while (pg_idx < nr_pages) {
 			struct page *page = pages[pg_idx];
···
 	struct bio_vec bv;
 	unsigned nr_ptrs = k.k->type == KEY_TYPE_reflink_v
 		? 0 : bch2_bkey_nr_ptrs_fully_allocated(k);
-	unsigned state = bkey_to_sector_state(k.k);
+	unsigned state = bkey_to_sector_state(k);
 
 	bio_for_each_segment(bv, bio, iter)
 		__bch2_page_state_set(bv.bv_page, bv.bv_offset >> 9,
···
 			goto bkey_err;
 
 		/* already reserved */
-		if (k.k->type == KEY_TYPE_reservation &&
-		    bkey_s_c_to_reservation(k).v->nr_replicas >= opts.data_replicas) {
+		if (bkey_extent_is_reservation(k) &&
+		    bch2_bkey_nr_ptrs_fully_allocated(k) >= opts.data_replicas) {
 			bch2_btree_iter_advance(&iter);
 			continue;
 		}

fs/bcachefs/fs.c

···
 			int flags2 = 0;
 			u64 offset = p.ptr.offset;
 
+			if (p.ptr.unwritten)
+				flags2 |= FIEMAP_EXTENT_UNWRITTEN;
+
 			if (p.crc.compression_type)
 				flags2 |= FIEMAP_EXTENT_ENCODED;
 			else

fs/bcachefs/fsck.c

···
 			continue;
 
 		if (fsck_err_on(!(i->inode.bi_flags & BCH_INODE_I_SIZE_DIRTY) &&
-				k.k->type != KEY_TYPE_reservation &&
-				k.k->p.offset > round_up(i->inode.bi_size, block_bytes(c)) >> 9, c,
+				k.k->p.offset > round_up(i->inode.bi_size, block_bytes(c)) >> 9 &&
+				!bkey_extent_is_reservation(k), c,
 				"extent type past end of inode %llu:%u, i_size %llu\n  %s",
 				i->inode.bi_inum, i->snapshot, i->inode.bi_size,
 				(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {

fs/bcachefs/io.c

···
 	if (bch2_bkey_has_target(c, k, opts.promote_target))
 		return false;
 
+	if (bkey_extent_is_unwritten(k))
+		return false;
+
 	if (bch2_target_congested(c, opts.promote_target)) {
 		/* XXX trace this */
 		return false;

fs/bcachefs/reflink.c

···
 	struct bkey_s_c k;
 	int ret;
 
-	for_each_btree_key_upto_continue_norestart(*iter, end, 0, k, ret)
+	for_each_btree_key_upto_continue_norestart(*iter, end, 0, k, ret) {
+		if (bkey_extent_is_unwritten(k))
+			continue;
+
 		if (bkey_extent_is_data(k.k))
 			return k;
+	}
 
 	if (bkey_ge(iter->pos, end))
 		bch2_btree_iter_set_pos(iter, end);