libkvs: Support flux_kvs_namespace_create_with()

Problem: libkvs does not support a way to initialize a namespace
to a specific rootref.

Solution: Add a new function flux_kvs_namespace_create_with().

doc/man3/flux_kvs_namespace_create.rst

@@ -17,6 +17,14 @@ SYNOPSIS
                                              uint32_t owner,
                                              int flags);
 
+::
+
+   flux_future_t *flux_kvs_namespace_create_with (flux_t *h,
+                                                  const char *namespace,
+                                                  const char *rootref,
+                                                  uint32_t owner,
+                                                  int flags);
+
 ::
 
    flux_future_t *flux_kvs_namespace_remove (flux_t *h,
@@ -32,6 +40,11 @@ other KVS namespaces. An owner of the namespace other than the
 instance owner can be chosen by setting *owner*. Otherwise, *owner*
 can be set to FLUX_USERID_UNKNOWN.
 
+``flux_kvs_namespace_create_with()`` is identical to
+``flux_kvs_namespace_create()`` but will initialize the namespace to
+the specified *rootref*.  This may be useful in several circumstances,
+such as initializing a namespace to an earlier checkpoint.
+
 ``flux_kvs_namespace_remove()`` removes a KVS namespace.
 
 

src/common/libkvs/kvs.c

@@ -65,6 +65,24 @@ flux_future_t *flux_kvs_namespace_create (flux_t *h, const char *ns,
     return rv;
 }
 
+flux_future_t *flux_kvs_namespace_create_with (flux_t *h, const char *ns,
+                                               const char *rootref,
+                                               uint32_t owner, int flags)
+{
+    if (!ns || !rootref || flags) {
+        errno = EINVAL;
+        return NULL;
+    }
+
+    /* N.B. owner cast to int */
+    return flux_rpc_pack (h, "kvs.namespace-create", 0, 0,
+                          "{ s:s s:s s:i s:i }",
+                          "namespace", ns,
+                          "rootref", rootref,
+                          "owner", owner,
+                          "flags", flags);
+}
+
 flux_future_t *flux_kvs_namespace_remove (flux_t *h, const char *ns)
 {
     if (!ns) {

src/common/libkvs/kvs.h

@@ -49,6 +49,9 @@ enum kvs_op {
  */
 flux_future_t *flux_kvs_namespace_create (flux_t *h, const char *ns,
                                           uint32_t owner, int flags);
+flux_future_t *flux_kvs_namespace_create_with (flux_t *h, const char *ns,
+                                               const char *rootref,
+                                               uint32_t owner, int flags);
 flux_future_t *flux_kvs_namespace_remove (flux_t *h, const char *ns);
 
 /* Synchronization:

src/common/libkvs/test/kvs.c

@@ -27,6 +27,11 @@ void errors (void)
     ok (flux_kvs_namespace_create (NULL, NULL, 0, 5) == NULL && errno == EINVAL,
         "flux_kvs_namespace_create fails on bad input");
 
+    errno = 0;
+    ok (flux_kvs_namespace_create_with (NULL, NULL, NULL, 0, 5) == NULL
+        && errno == EINVAL,
+        "flux_kvs_namespace_create_with fails on bad input");
+
     errno = 0;
     ok (flux_kvs_namespace_remove (NULL, NULL) == NULL && errno == EINVAL,
         "flux_kvs_namespace_remove fails on bad input");