On Tue, Jun 18, 2019 at 02:14:40PM -0700, Matthias Kaehlcke wrote: > empty_child_inc/dec() use the ternary operator for conditional > operations. The conditions involve the post/pre in/decrement > operator and the operation is only performed when the condition > is *not* true. This is hard to parse for humans, use a regular > 'if' construct instead and perform the in/decrement separately. > > This also fixes two warnings that are emitted about the value > of the ternary expression being unused, when building the kernel > with clang + "kbuild: Remove unnecessary -Wno-unused-value" > (https://lore.kernel.org/patchwork/patch/1089869/): > > CC net/ipv4/fib_trie.o > net/ipv4/fib_trie.c:351:2: error: expression result unused > [-Werror,-Wunused-value] > ++tn_info(n)->empty_children ? : ++tn_info(n)->full_children; >
As an FYI, this is also being fixed in clang: https://bugs.llvm.org/show_bug.cgi?id=42239 https://reviews.llvm.org/D63369 > Signed-off-by: Matthias Kaehlcke <[email protected]> > --- > I have no good understanding of the fib_trie code, but the > disentangled code looks wrong, and it should be equivalent to the > cryptic version, unless I messed it up. In empty_child_inc() > 'full_children' is only incremented when 'empty_children' is -1. I > suspect a bug in the cryptic code, but am surprised why it hasn't > blown up yet. Or is it intended behavior that is just > super-counterintuitive? > > For now I'm leaving it at disentangling the cryptic expressions, > if there is a bug we can discuss what action to take. > --- > net/ipv4/fib_trie.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c > index 868c74771fa9..cf7788e336b7 100644 > --- a/net/ipv4/fib_trie.c > +++ b/net/ipv4/fib_trie.c > @@ -338,12 +338,18 @@ static struct tnode *tnode_alloc(int bits) > > static inline void empty_child_inc(struct key_vector *n) > { > - ++tn_info(n)->empty_children ? : ++tn_info(n)->full_children; > + tn_info(n)->empty_children++; > + > + if (!tn_info(n)->empty_children) > + tn_info(n)->full_children++; > } > > static inline void empty_child_dec(struct key_vector *n) > { > - tn_info(n)->empty_children-- ? : tn_info(n)->full_children--; > + if (!tn_info(n)->empty_children) > + tn_info(n)->full_children--; > + > + tn_info(n)->empty_children--; > } > > static struct key_vector *leaf_new(t_key key, struct fib_alias *fa) > -- > 2.22.0.410.gd8fdbe21b5-goog >
