Re: [PATCH -next 2/2] bcache: Use max_t() when comparing different types

On Thu, 6 Feb 2014 21:45:36 +0100 Geert Uytterhoeven [off-list ref] wrote:

quoted

--- a/drivers/md/bcache/btree.c~bcache-drop-l-suffix-when-comparing-ssize_t-with-0-fix
+++ a/drivers/md/bcache/btree.c

@@ -1805,7 +1805,7 @@ static bool btree_insert_key(struct btre

 static size_t insert_u64s_remaining(struct btree *b)
 {
-       ssize_t ret = bch_btree_keys_u64s_remaining(&b->keys);
+       size_t ret = bch_btree_keys_u64s_remaining(&b->keys);

        /*
         * Might land in the middle of an existing extent and have to split it

@@ -1813,7 +1813,7 @@ static size_t insert_u64s_remaining(stru
        if (b->keys.ops->is_extents)
                ret -= KEY_MAX_U64S;

I think the reason is the line above: with size_t, ret may become a big
positive number when the subtraction wraps below zero.

Well, I assumed that case would be a bug - otherwise the programmer
would have commented such a subtlety.  Wouldn't he?

quoted

-       return max(ret, 0);
+       return max_t(size_t, ret, 0);

That part is OK, cfr. my v1 (which I had planned to send out as v3 again).

It needs to be ssize_t.