On Wed, Jan 15, 2014 at 12:06 PM, Joe Perches [off-list ref] wrote:

On Wed, 2014-01-15 at 10:06 +0100, Geert Uytterhoeven wrote:

quoted

drivers/md/bcache/btree.c: In function ‘insert_u64s_remaining’:
drivers/md/bcache/btree.c:1816: warning: comparison of distinct pointer types lacks a cast

[]

quoted

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c

[]

quoted

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

-     return max(ret, 0L);
+     return max_t(ssize_t, ret, 0L);

why not
        return max(ret, 0);

Indeed, that also works, on both 32-bit and 64-bit.
Will resend, now all the issues moved from -next to Linus' tree.

I think it odd that:

drivers/md/bcache/bset.h:static inline size_t bch_btree_keys_u64s_remaining(struct btree_keys *b)

and:

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

        /*
         * Might land in the middle of an existing extent and have to split it
         */
        if (b->keys.ops->is_extents)
                ret -= KEY_MAX_U64S;

        return max(ret, 0L);
}

so the only use of that size_t inline is cast to ssize_t

If the value returned by bch_btree_keys_u64s_remaining() is smaller
than KEY_MAX_U64S, it must stay negative after the subtraction,
instead of wrapping around to a big positive number. That's why ret is
ssize_t and not size_t.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds