bcachefs: clean up some dead fallocate code

The have_reservation local variable in bch2_extent_fallocate() is
initialized to false and set to true further down in the function.
Between this two points, one branch of code checks for negative
value and one for positive, and nothing ever checks the variable
after it is set to true. Clean up some of the unnecessary logic and
code.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/io_misc.c

@@ -34,8 +34,7 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 	struct open_buckets open_buckets = { 0 };
 	struct bkey_s_c k;
 	struct bkey_buf old, new;
-	unsigned sectors_allocated = 0;
-	bool have_reservation = false;
+	unsigned sectors_allocated = 0, new_replicas;
 	bool unwritten = opts.nocow &&
 	    c->sb.version >= bcachefs_metadata_version_unwritten_extents;
 	int ret;
@@ -50,28 +49,20 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 		return ret;
 
 	sectors = min_t(u64, sectors, k.k->p.offset - iter->pos.offset);
+	new_replicas = max(0, (int) opts.data_replicas -
+			   (int) bch2_bkey_nr_ptrs_fully_allocated(k));
 
-	if (!have_reservation) {
-		unsigned new_replicas =
-			max(0, (int) opts.data_replicas -
-			    (int) bch2_bkey_nr_ptrs_fully_allocated(k));
-		/*
-		 * Get a disk reservation before (in the nocow case) calling
-		 * into the allocator:
-		 */
-		ret = bch2_disk_reservation_get(c, &disk_res, sectors, new_replicas, 0);
-		if (unlikely(ret))
-			goto err_noprint;
-
-		bch2_bkey_buf_reassemble(&old, c, k);
-	}
+	/*
+	 * Get a disk reservation before (in the nocow case) calling
+	 * into the allocator:
+	 */
+	ret = bch2_disk_reservation_get(c, &disk_res, sectors, new_replicas, 0);
+	if (unlikely(ret))
+		goto err_noprint;
 
-	if (have_reservation) {
-		if (!bch2_extents_match(k, bkey_i_to_s_c(old.k)))
-			goto err;
+	bch2_bkey_buf_reassemble(&old, c, k);
 
-		bch2_key_resize(&new.k->k, sectors);
-	} else if (!unwritten) {
+	if (!unwritten) {
 		struct bkey_i_reservation *reservation;
 
 		bch2_bkey_buf_realloc(&new, c, sizeof(*reservation) / sizeof(u64));
@@ -118,8 +109,6 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 			ptr->unwritten = true;
 	}
 
-	have_reservation = true;
-
 	ret = bch2_extent_update(trans, inum, iter, new.k, &disk_res,
 				 0, i_sectors_delta, true);
 err: