bcachefs: Add option for completely disabling nocow

This adds an option for completely disabling nocow mode, including the
locking in the data move path.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/data_update.c

@@ -327,8 +327,9 @@ void bch2_data_update_exit(struct data_update *update)
 	const struct bch_extent_ptr *ptr;
 
 	bkey_for_each_ptr(ptrs, ptr) {
-		bch2_bucket_nocow_unlock(&c->nocow_locks,
-					 PTR_BUCKET_POS(c, ptr), 0);
+		if (c->opts.nocow_enabled)
+			bch2_bucket_nocow_unlock(&c->nocow_locks,
+						 PTR_BUCKET_POS(c, ptr), 0);
 		percpu_ref_put(&bch_dev_bkey_exists(c, ptr->dev)->ref);
 	}
 
@@ -488,23 +489,26 @@ int bch2_data_update_init(struct btree_trans *trans,
 		if (p.crc.compression_type == BCH_COMPRESSION_TYPE_incompressible)
 			m->op.incompressible = true;
 
-		if (ctxt) {
-			move_ctxt_wait_event(ctxt, trans,
-					(locked = bch2_bucket_nocow_trylock(&c->nocow_locks,
-								  PTR_BUCKET_POS(c, &p.ptr), 0)) ||
-					!atomic_read(&ctxt->read_sectors));
-
-			if (!locked)
-				bch2_bucket_nocow_lock(&c->nocow_locks,
-						       PTR_BUCKET_POS(c, &p.ptr), 0);
-		} else {
-			if (!bch2_bucket_nocow_trylock(&c->nocow_locks,
-						       PTR_BUCKET_POS(c, &p.ptr), 0)) {
-				ret = -BCH_ERR_nocow_lock_blocked;
-				goto err;
+		if (c->opts.nocow_enabled) {
+			if (ctxt) {
+				move_ctxt_wait_event(ctxt, trans,
+						(locked = bch2_bucket_nocow_trylock(&c->nocow_locks,
+									  PTR_BUCKET_POS(c, &p.ptr), 0)) ||
+						!atomic_read(&ctxt->read_sectors));
+
+				if (!locked)
+					bch2_bucket_nocow_lock(&c->nocow_locks,
+							       PTR_BUCKET_POS(c, &p.ptr), 0);
+			} else {
+				if (!bch2_bucket_nocow_trylock(&c->nocow_locks,
+							       PTR_BUCKET_POS(c, &p.ptr), 0)) {
+					ret = -BCH_ERR_nocow_lock_blocked;
+					goto err;
+				}
 			}
+			ptrs_locked |= (1U << i);
 		}
-		ptrs_locked |= (1U << i);
+
 		i++;
 	}
 

fs/bcachefs/io.c

@@ -1649,7 +1649,7 @@ static void __bch2_write(struct bch_write_op *op)
 
 	nofs_flags = memalloc_nofs_save();
 
-	if (unlikely(op->opts.nocow)) {
+	if (unlikely(op->opts.nocow && c->opts.nocow_enabled)) {
 		bch2_nocow_write(op);
 		if (op->flags & BCH_WRITE_DONE)
 			goto out_nofs_restore;

fs/bcachefs/opts.h

@@ -404,6 +404,12 @@ enum opt_type {
 	  NULL,		"Nocow mode: Writes will be done in place when possible.\n"\
 			"Snapshots and reflink will still caused writes to be COW\n"\
 			"Implicitly disables data checksumming, compression and encryption")\
+	x(nocow_enabled,		u8,				\
+	  OPT_FS|OPT_MOUNT,						\
+	  OPT_BOOL(),							\
+	  BCH2_NO_SB_OPT,			true,			\
+	  NULL,		"Enable nocow mode: enables runtime locking in\n"\
+			"data move path needed if nocow will ever be in use\n")\
 	x(no_data_io,			u8,				\
 	  OPT_MOUNT,							\
 	  OPT_BOOL(),							\