From 10f0f744c4b0f8ac5332effcd03b7438121ebf6e Mon Sep 17 00:00:00 2001
From: Daniel Milroy <daniel.milroy@gmail.com>
Date: Tue, 14 Jan 2025 18:23:56 -0800
Subject: [PATCH] reapi: add shrink function to C++ API

---
 resource/reapi/bindings/c++/reapi.hpp         | 16 +++++++
 resource/reapi/bindings/c++/reapi_cli.hpp     |  2 +
 .../reapi/bindings/c++/reapi_cli_impl.hpp     | 48 +++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/resource/reapi/bindings/c++/reapi.hpp b/resource/reapi/bindings/c++/reapi.hpp
index eee25b58b..5fd344033 100644
--- a/resource/reapi/bindings/c++/reapi.hpp
+++ b/resource/reapi/bindings/c++/reapi.hpp
@@ -204,6 +204,22 @@ class reapi_t {
         return -1;
     }
 
+    /*! Update the resource state with R.
+     *
+     *  \param h         Opaque handle. How it is used is an implementation
+     *                   detail. However, when it is used within a Flux's
+     *                   service module, it is expected to be a pointer
+     *                   to a flux_t object.
+     *  \param subgraph_path String representing the path from the cluster root
+     *                   to the root of the subgraph to be removed from
+     *                   the resource graph
+     *  \return          0 on success; -1 on error.
+     */
+    static int shrink (void *h, const std::string &subgraph_path)
+    {
+        return -1;
+    }
+
     /*! Cancel the allocation or reservation corresponding to jobid.
      *
      *  \param h         Opaque handle. How it is used is an implementation
diff --git a/resource/reapi/bindings/c++/reapi_cli.hpp b/resource/reapi/bindings/c++/reapi_cli.hpp
index 1892b0131..77e5fcee0 100644
--- a/resource/reapi/bindings/c++/reapi_cli.hpp
+++ b/resource/reapi/bindings/c++/reapi_cli.hpp
@@ -90,6 +90,7 @@ class resource_query_t {
     int remove_job (const uint64_t jobid);
     int remove_job (const uint64_t jobid, const std::string &R, bool &full_removal);
     int grow (const std::string &R_subgraph);
+    int shrink (const std::string &subgraph_path);
     void incr_job_counter ();
 
     /* Run the traverser to match the jobspec */
@@ -150,6 +151,7 @@ class reapi_cli_t : public reapi_t {
                                 double &ov,
                                 std::string &R_out);
     static int grow (void *h, const std::string &R_subgraph);
+    static int shrink (void *h, const std::string &subgraph_path);
     static int cancel (void *h, const uint64_t jobid, bool noent_ok);
     static int cancel (void *h,
                        const uint64_t jobid,
diff --git a/resource/reapi/bindings/c++/reapi_cli_impl.hpp b/resource/reapi/bindings/c++/reapi_cli_impl.hpp
index 5e3335a0d..57df3ebf3 100644
--- a/resource/reapi/bindings/c++/reapi_cli_impl.hpp
+++ b/resource/reapi/bindings/c++/reapi_cli_impl.hpp
@@ -178,6 +178,19 @@ int reapi_cli_t::grow (void *h, const std::string &R_subgraph)
     return rc;
 }
 
+int reapi_cli_t::shrink (void *h, const std::string &subgraph_path)
+{
+    resource_query_t *rq = static_cast<resource_query_t *> (h);
+    int rc = -1;
+
+    if ((rc = rq->shrink (subgraph_path)) != 0) {
+        m_err_msg += __FUNCTION__;
+        m_err_msg += ": ERROR: shrink error: " + std::string (strerror (errno)) + "\n";
+    }
+
+    return rc;
+}
+
 int reapi_cli_t::match_allocate_multi (void *h,
                                        bool orelse_reserve,
                                        const char *jobs,
@@ -769,6 +782,41 @@ int resource_query_t::grow (const std::string &R_subgraph)
     return rc;
 }
 
+int resource_query_t::shrink (const std::string &subgraph_path)
+{
+    int rc = -1;
+    std::shared_ptr<resource_reader_base_t> reader;
+
+    if (subgraph_path == "") {
+        errno = EINVAL;
+        return rc;
+    }
+    if (params.load_format != "jgf") {
+        m_err_msg = __FUNCTION__;
+        m_err_msg += ": ERROR: shrinking a resource graph not ";
+        m_err_msg += " initialized with JGF is unsupported\n";
+        errno = ENOTSUP;
+        return rc;
+    }
+    if ((reader = create_resource_reader ("jgf")) == nullptr) {
+        m_err_msg = __FUNCTION__;
+        m_err_msg += ": ERROR: can't create JGF reader\n";
+        return rc;
+    }
+    if ((rc = reader->remove_subgraph (db->resource_graph, db->metadata, subgraph_path)) != 0) {
+        m_err_msg = __FUNCTION__;
+        m_err_msg += ": ERROR: reader returned error: ";
+        m_err_msg += reader->err_message () + "\n";
+        return rc;
+    }
+    if ((rc = traverser->initialize (db, matcher)) != 0) {
+        m_err_msg = __FUNCTION__;
+        m_err_msg += ": ERROR: reinitialize traverser after shrink. ";
+        m_err_msg += reader->err_message () + "\n";
+    }
+    return rc;
+}
+
 void resource_query_t::incr_job_counter ()
 {
     jobid_counter++;