[PATCH 09/11] tools/xenstore: add hashtable_replace() function

[Juergen Gross <jgross@xxxxxxxx>]

For an effective way to replace a hashtable entry add a new function
hashtable_replace().

While at it let hashtable_add() fail if an entry with the specified
key does already exist.

This is in preparation to replace TDB with a more simple data storage.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 tools/xenstore/hashtable.c | 52 ++++++++++++++++++++++++++++++--------
 tools/xenstore/hashtable.h | 16 ++++++++++++
 2 files changed, 58 insertions(+), 10 deletions(-)

diff --git a/tools/xenstore/hashtable.c b/tools/xenstore/hashtable.c
index 9daddd9782..f358bec5ae 100644
--- a/tools/xenstore/hashtable.c
+++ b/tools/xenstore/hashtable.c
@@ -141,11 +141,32 @@ static int hashtable_expand(struct hashtable *h)
     return 0;
 }
 
+static struct entry *hashtable_search_entry(const struct hashtable *h,
+                                           const void *k)
+{
+    struct entry *e;
+    unsigned int hashvalue, index;
+
+    hashvalue = hash(h, k);
+    index = indexFor(h->tablelength,hashvalue);
+    e = h->table[index];
+    while (NULL != e)
+    {
+        /* Check hash value to short circuit heavier comparison */
+        if ((hashvalue == e->h) && (h->eqfn(k, e->k))) return e;
+        e = e->next;
+    }
+    return NULL;
+}
+
 int hashtable_add(struct hashtable *h, const void *k, void *v)
 {
-    /* This method allows duplicate keys - but they shouldn't be used */
     unsigned int index;
     struct entry *e;
+
+    if (hashtable_search_entry(h, k))
+        return EEXIST;
+
     if (++(h->entrycount) > h->loadlimit)
     {
         /* Ignore the return value. If expand fails, we should
@@ -176,17 +197,28 @@ int hashtable_add(struct hashtable *h, const void *k, 
void *v)
 void *hashtable_search(const struct hashtable *h, const void *k)
 {
     struct entry *e;
-    unsigned int hashvalue, index;
-    hashvalue = hash(h,k);
-    index = indexFor(h->tablelength,hashvalue);
-    e = h->table[index];
-    while (NULL != e)
+
+    e = hashtable_search_entry(h, k);
+    return e ? e->v : NULL;
+}
+
+int hashtable_replace(struct hashtable *h, const void *k, void *v)
+{
+    struct entry *e;
+
+    e = hashtable_search_entry(h, k);
+    if (!e)
+        return ENOENT;
+
+    if (h->flags & HASHTABLE_FREE_VALUE)
     {
-        /* Check hash value to short circuit heavier comparison */
-        if ((hashvalue == e->h) && (h->eqfn(k, e->k))) return e->v;
-        e = e->next;
+        talloc_free(e->v);
+        talloc_steal(e, v);
     }
-    return NULL;
+
+    e->v = v;
+
+    return 0;
 }
 
 void
diff --git a/tools/xenstore/hashtable.h b/tools/xenstore/hashtable.h
index 792f6cda7b..214aea1b3d 100644
--- a/tools/xenstore/hashtable.h
+++ b/tools/xenstore/hashtable.h
@@ -51,6 +51,22 @@ create_hashtable(const void *ctx, const char *name,
 int
 hashtable_add(struct hashtable *h, const void *k, void *v);
 
+/*****************************************************************************
+ * hashtable_replace
+
+ * @name        hashtable_nsert
+ * @param   h   the hashtable to insert into
+ * @param   k   the key - hashtable claims ownership and will free on removal
+ * @param   v   the value - does not claim ownership
+ * @return      zero for successful insertion
+ *
+ * This function does check for an entry being present before replacing it
+ * with a new value.
+ */
+
+int
+hashtable_replace(struct hashtable *h, const void *k, void *v);
+
 /*****************************************************************************
  * hashtable_search
    
-- 
2.35.3