shash: New "smap" functions for working with string-to-string maps.

An shash always has string keys and sometimes it hash string values as
well.  Usually the general-purpose shash functions are fine for working
with string-to-string maps, but this commit introduces a few more
specialized functions that only work with string-to-string maps.  It's not
clear yet to me whether this should actually be a new data structure, so
for now the new functions just work on shashes.

This commit also converts one user of shash_destroy() to use smap_destroy().
This is the only existing user of these functions that I spotted as a
trivial conversion candidate while grepping.

These new functions will see more use in the following commit.

Reviewed by Justin Pettit.

3 files changed, 61 insertions, 5 deletions

diff --git a/lib/shash.c b/lib/shash.c
index 82791e31f..3269a4108 100644
--- a/lib/shash.c
+++ b/lib/shash.c
@@ -303,3 +303,57 @@ shash_random_node(struct shash *sh)
 {
     return CONTAINER_OF(hmap_random_node(&sh->map), struct shash_node, node);
 }
+
+/* String-to-string maps (smaps). */
+
+/* Frees 'smap', including its keys and string values. */
+void
+smap_destroy(struct shash *smap)
+{
+    shash_destroy_free_data(smap);
+}
+
+/* Returns true if string-to-string maps 'a' and 'b' contain the same keys and
+ * values, false otherwise. */
+bool
+smap_equal(const struct shash *a, const struct shash *b)
+{
+    struct shash_node *a_node;
+
+    if (shash_count(a) != shash_count(b)) {
+        return false;
+    }
+
+    SHASH_FOR_EACH (a_node, a) {
+        uint32_t hash = a_node->node.hash;
+        struct shash_node *b_node = shash_find__(b, a_node->name, hash);
+        if (!b_node || strcmp(a_node->data, b_node->data)) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+/* Initializes 'dst' as a clone of 'src'. */
+void
+smap_clone(struct shash *dst, const struct shash *src)
+{
+    struct shash_node *node;
+
+    shash_init(dst);
+    SHASH_FOR_EACH (node, src) {
+        shash_add_nocopy__(dst, xstrdup(node->name), xstrdup(node->data),
+                           node->node.hash);
+    }
+}
+
+/* Adds 'key' with string 'value' to 'smap', making a copy of each.
+ *
+ * It is the caller's responsibility to avoid duplicate names, if that is
+ * desirable. */
+void
+smap_add(struct shash *smap, const char *key, const char *value)
+{
+    shash_add(smap, key, xstrdup(value));
+}
diff --git a/lib/shash.h b/lib/shash.h
index dfb10e2cc..1210772ef 100644
--- a/lib/shash.h
+++ b/lib/shash.h
@@ -66,6 +66,12 @@ const struct shash_node **shash_sort(const struct shash *);
 bool shash_equal_keys(const struct shash *, const struct shash *);
 struct shash_node *shash_random_node(struct shash *);
 
+/* Working with "smaps": shashes used as string-to-string maps. */
+void smap_destroy(struct shash *);
+bool smap_equal(const struct shash *, const struct shash *);
+void smap_clone(struct shash *, const struct shash *);
+void smap_add(struct shash *, const char *key, const char *value);
+
 #ifdef  __cplusplus
 }
 #endif
diff --git a/utilities/ovs-vsctl.c b/utilities/ovs-vsctl.c
index 8df033087..c2c67ad8b 100644
--- a/utilities/ovs-vsctl.c
+++ b/utilities/ovs-vsctl.c
@@ -3180,7 +3180,6 @@ do_vsctl(const char *args, struct vsctl_command *commands, size_t n_commands,
 
     for (c = commands; c < &commands[n_commands]; c++) {
         struct ds *ds = &c->output;
-        struct shash_node *node;
 
         if (oneline) {
             size_t j;
@@ -3207,10 +3206,7 @@ do_vsctl(const char *args, struct vsctl_command *commands, size_t n_commands,
         }
         ds_destroy(&c->output);
 
-        SHASH_FOR_EACH (node, &c->options) {
-            free(node->data);
-        }
-        shash_destroy(&c->options);
+        smap_destroy(&c->options);
     }
     free(commands);