bcachefs: Start using bpos.snapshot field

This patch starts treating the bpos.snapshot field like part of the key
in the btree code:

* bpos_successor() and bpos_predecessor() now include the snapshot field
* Keys in btrees that will be using snapshots (extents, inodes, dirents
  and xattrs) now always have their snapshot field set to U32_MAX

The btree iterator code gets a new flag, BTREE_ITER_ALL_SNAPSHOTS, that
determines whether we're iterating over keys in all snapshots or not -
internally, this controlls whether bkey_(successor|predecessor)
increment/decrement the snapshot field, or only the higher bits of the
key.

We add a new member to struct btree_iter, iter->snapshot: when
BTREE_ITER_ALL_SNAPSHOTS is not set, iter->pos.snapshot should always
equal iter->snapshot, which will be 0 for btrees that don't use
snapshots, and alsways U32_MAX for btrees that will use snapshots
(until we enable snapshot creation).

This patch also introduces a new metadata version number, and compat
code for reading from/writing to older versions - this isn't a forced
upgrade (yet).

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 32 insertions, 10 deletions

diff --git a/fs/bcachefs/bkey.h b/fs/bcachefs/bkey.h
index df23c5b48969..72b4267031d8 100644
--- a/fs/bcachefs/bkey.h
+++ b/fs/bcachefs/bkey.h
@@ -258,24 +258,46 @@ static inline unsigned bkey_format_key_bits(const struct bkey_format *format)
 		format->bits_per_field[BKEY_FIELD_SNAPSHOT];
 }
 
-static inline struct bpos bkey_successor(struct bpos p)
+static inline struct bpos bpos_successor(struct bpos p)
 {
-	struct bpos ret = p;
+	if (!++p.snapshot &&
+	    !++p.offset &&
+	    !++p.inode)
+		BUG();
 
-	if (!++ret.offset)
-		BUG_ON(!++ret.inode);
+	return p;
+}
 
-	return ret;
+static inline struct bpos bpos_predecessor(struct bpos p)
+{
+	if (!p.snapshot-- &&
+	    !p.offset-- &&
+	    !p.inode--)
+		BUG();
+
+	return p;
 }
 
-static inline struct bpos bkey_predecessor(struct bpos p)
+static inline struct bpos bpos_nosnap_successor(struct bpos p)
 {
-	struct bpos ret = p;
+	p.snapshot = 0;
 
-	if (!ret.offset--)
-		BUG_ON(!ret.inode--);
+	if (!++p.offset &&
+	    !++p.inode)
+		BUG();
 
-	return ret;
+	return p;
+}
+
+static inline struct bpos bpos_nosnap_predecessor(struct bpos p)
+{
+	p.snapshot = 0;
+
+	if (!p.offset-- &&
+	    !p.inode--)
+		BUG();
+
+	return p;
 }
 
 static inline u64 bkey_start_offset(const struct bkey *k)