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, 11 insertions, 6 deletions

diff --git a/fs/bcachefs/bkey.c b/fs/bcachefs/bkey.c
index 8b2befac95d4..a0379f980f7e 100644
--- a/fs/bcachefs/bkey.c
+++ b/fs/bcachefs/bkey.c
@@ -617,15 +617,19 @@ const char *bch2_bkey_format_validate(struct bkey_format *f)
 		return "incorrect number of fields";
 
 	for (i = 0; i < f->nr_fields; i++) {
+		unsigned unpacked_bits = bch2_bkey_format_current.bits_per_field[i];
+		u64 unpacked_mask = ~((~0ULL << 1) << (unpacked_bits - 1));
 		u64 field_offset = le64_to_cpu(f->field_offset[i]);
 
-		if (f->bits_per_field[i] > 64)
+		if (f->bits_per_field[i] > unpacked_bits)
 			return "field too large";
 
-		if (field_offset &&
-		    (f->bits_per_field[i] == 64 ||
-		    (field_offset + ((1ULL << f->bits_per_field[i]) - 1) <
-		     field_offset)))
+		if ((f->bits_per_field[i] == unpacked_bits) && field_offset)
+			return "offset + bits overflow";
+
+		if (((field_offset + ((1ULL << f->bits_per_field[i]) - 1)) &
+		     unpacked_mask) <
+		    field_offset)
 			return "offset + bits overflow";
 
 		bits += f->bits_per_field[i];
@@ -1126,11 +1130,12 @@ void bch2_bkey_pack_test(void)
 	struct bkey_packed p;
 
 	struct bkey_format test_format = {
-		.key_u64s	= 2,
+		.key_u64s	= 3,
 		.nr_fields	= BKEY_NR_FIELDS,
 		.bits_per_field = {
 			13,
 			64,
+			32,
 		},
 	};