qht: require a default comparison function

qht_lookup now uses the default cmp function. qht_lookup_custom is defined
to retain the old behaviour, that is a cmp function is explicitly provided.

qht_insert will gain use of the default cmp in the next patch.

Note that we move qht_lookup_custom's @func to be the last argument,
which makes the new qht_lookup as simple as possible.
Instead of this (i.e. keeping @func 2nd):
0000000000010750 <qht_lookup>:
   10750:       89 d1                   mov    %edx,%ecx
   10752:       48 89 f2                mov    %rsi,%rdx
   10755:       48 8b 77 08             mov    0x8(%rdi),%rsi
   10759:       e9 22 ff ff ff          jmpq   10680 <qht_lookup_custom>
   1075e:       66 90                   xchg   %ax,%ax

We get:
0000000000010740 <qht_lookup>:
   10740:       48 8b 4f 08             mov    0x8(%rdi),%rcx
   10744:       e9 37 ff ff ff          jmpq   10680 <qht_lookup_custom>
   10749:       0f 1f 80 00 00 00 00    nopl   0x0(%rax)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 20 insertions, 5 deletions

diff --git a/include/qemu/qht.h b/include/qemu/qht.h
index 531aa95325..5f03a0f4cb 100644
--- a/include/qemu/qht.h
+++ b/include/qemu/qht.h
@@ -11,8 +11,11 @@
 #include "qemu/thread.h"
 #include "qemu/qdist.h"
 
+typedef bool (*qht_cmp_func_t)(const void *a, const void *b);
+
 struct qht {
     struct qht_map *map;
+    qht_cmp_func_t cmp;
     QemuMutex lock; /* serializes setters of ht->map */
     unsigned int mode;
 };
@@ -47,10 +50,12 @@ typedef void (*qht_iter_func_t)(struct qht *ht, void *p, uint32_t h, void *up);
 /**
  * qht_init - Initialize a QHT
  * @ht: QHT to be initialized
+ * @cmp: default comparison function. Cannot be NULL.
  * @n_elems: number of entries the hash table should be optimized for.
  * @mode: bitmask with OR'ed QHT_MODE_*
  */
-void qht_init(struct qht *ht, size_t n_elems, unsigned int mode);
+void qht_init(struct qht *ht, qht_cmp_func_t cmp, size_t n_elems,
+              unsigned int mode);
 
 /**
  * qht_destroy - destroy a previously initialized QHT
@@ -78,11 +83,11 @@ void qht_destroy(struct qht *ht);
 bool qht_insert(struct qht *ht, void *p, uint32_t hash);
 
 /**
- * qht_lookup - Look up a pointer in a QHT
+ * qht_lookup_custom - Look up a pointer using a custom comparison function.
  * @ht: QHT to be looked up
- * @func: function to compare existing pointers against @userp
  * @userp: pointer to pass to @func
  * @hash: hash of the pointer to be looked up
+ * @func: function to compare existing pointers against @userp
  *
  * Needs to be called under an RCU read-critical section.
  *
@@ -94,8 +99,18 @@ bool qht_insert(struct qht *ht, void *p, uint32_t hash);
  * Returns the corresponding pointer when a match is found.
  * Returns NULL otherwise.
  */
-void *qht_lookup(struct qht *ht, qht_lookup_func_t func, const void *userp,
-                 uint32_t hash);
+void *qht_lookup_custom(struct qht *ht, const void *userp, uint32_t hash,
+                        qht_lookup_func_t func);
+
+/**
+ * qht_lookup - Look up a pointer in a QHT
+ * @ht: QHT to be looked up
+ * @userp: pointer to pass to the comparison function
+ * @hash: hash of the pointer to be looked up
+ *
+ * Calls qht_lookup_custom() using @ht's default comparison function.
+ */
+void *qht_lookup(struct qht *ht, const void *userp, uint32_t hash);
 
 /**
  * qht_remove - remove a pointer from the hash table