bcachefs: BCH_SB_MEMBER_INVALID

Create a sentinal value for "invalid device".

This is needed for removing devices that have stripes on them (force
removing, without evacuating); we need a sentinal value for the stripe
pointers to the device being removed.

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

fs/bcachefs/replicas.c

@@ -82,7 +82,8 @@ int bch2_replicas_entry_validate(struct bch_replicas_entry_v1 *r,
 	}
 
 	for (unsigned i = 0; i < r->nr_devs; i++)
-		if (!bch2_member_exists(sb, r->devs[i])) {
+		if (r->devs[i] != BCH_SB_MEMBER_INVALID &&
+		    !bch2_member_exists(sb, r->devs[i])) {
 			prt_printf(err, "invalid device %u in entry ", r->devs[i]);
 			goto bad;
 		}

fs/bcachefs/sb-members.c

@@ -11,7 +11,8 @@
 
 void bch2_dev_missing(struct bch_fs *c, unsigned dev)
 {
-	bch2_fs_inconsistent(c, "pointer to nonexistent device %u", dev);
+	if (dev != BCH_SB_MEMBER_INVALID)
+		bch2_fs_inconsistent(c, "pointer to nonexistent device %u", dev);
 }
 
 void bch2_dev_bucket_missing(struct bch_fs *c, struct bpos bucket)

fs/bcachefs/sb-members_format.h

@@ -8,6 +8,11 @@
  */
 #define BCH_SB_MEMBERS_MAX		64
 
+/*
+ * Sentinal value - indicates a device that does not exist
+ */
+#define BCH_SB_MEMBER_INVALID		255
+
 #define BCH_MIN_NR_NBUCKETS	(1 << 6)
 
 #define BCH_IOPS_MEASUREMENTS()			\