[RFC PATCH 4/5] qmp: Added qemu-ebpf-rss-path command.

[Andrew Melnychenko <andrew@daynix.com>]

New qmp command to query ebpf helper.
It's crucial that qemu and helper are in sync and in touch.
Technically helper should pass eBPF fds that qemu may accept.
And different qemu's builds may have different eBPF programs and helpers.
Qemu returns helper that should "fit" to virtio-net.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
---
 monitor/qmp-cmds.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++
 qapi/misc.json     | 29 +++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
index f7d64a6457..5dd2a58ea2 100644
--- a/monitor/qmp-cmds.c
+++ b/monitor/qmp-cmds.c
@@ -351,3 +351,81 @@ void qmp_display_reload(DisplayReloadOptions *arg, Error **errp)
         abort();
     }
 }
+
+#ifdef CONFIG_LINUX
+
+static const char *get_dirname(char *path)
+{
+    char *sep;
+
+    sep = strrchr(path, '/');
+    if (sep == path) {
+        return "/";
+    } else if (sep) {
+        *sep = 0;
+        return path;
+    }
+    return ".";
+}
+
+static char *find_helper(const char *name)
+{
+    char qemu_exec[PATH_MAX];
+    const char *qemu_dir = NULL;
+    char *helper = NULL;
+
+    if (name == NULL) {
+        return NULL;
+    }
+
+    if (readlink("/proc/self/exe", qemu_exec, PATH_MAX) > 0) {
+        qemu_dir = get_dirname(qemu_exec);
+
+        helper = g_strdup_printf("%s/%s", qemu_dir, name);
+        if (access(helper, F_OK) == 0) {
+            return helper;
+        }
+        g_free(helper);
+    }
+
+    helper = g_strdup_printf("%s/%s", CONFIG_QEMU_HELPERDIR, name);
+    if (access(helper, F_OK) == 0) {
+        return helper;
+    }
+    g_free(helper);
+
+    return NULL;
+}
+
+HelperPathList *qmp_query_helper_paths(Error **errp)
+{
+    HelperPathList *ret = NULL;
+    const char *helpers_list[] = {
+#ifdef CONFIG_EBPF
+        "qemu-ebpf-rss-helper",
+#endif
+        NULL
+    };
+    const char **helper_iter = helpers_list;
+
+    for (; *helper_iter != NULL; ++helper_iter) {
+        char *path = find_helper(*helper_iter);
+        if (path) {
+            HelperPath *helper = g_new0(HelperPath, 1);
+            helper->name = g_strdup(*helper_iter);
+            helper->path = path;
+
+            QAPI_LIST_PREPEND(ret, helper);
+        }
+    }
+
+    return ret;
+}
+#else
+
+HelperPathList *qmp_query_helper_paths(Error **errp)
+{
+    return NULL;
+}
+
+#endif
diff --git a/qapi/misc.json b/qapi/misc.json
index 156f98203e..023bd2120d 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -519,3 +519,32 @@
  'data': { '*option': 'str' },
  'returns': ['CommandLineOptionInfo'],
  'allow-preconfig': true }
+
+##
+# @HelperPath:
+#
+# Name of the helper and binary location.
+##
+{ 'struct': 'HelperPath',
+  'data': {'name': 'str', 'path': 'str'} }
+
+##
+# @query-helper-paths:
+#
+# Query specific eBPF RSS helper for current qemu binary.
+#
+# Returns: list of object that contains name and path for helper.
+#
+# Example:
+#
+# -> { "execute": "query-helper-paths" }
+# <- { "return": [
+#        {
+#          "name": "qemu-ebpf-rss-helper",
+#          "path": "/usr/local/libexec/qemu-ebpf-rss-helper"
+#        }
+#      ]
+#    }
+#
+##
+{ 'command': 'query-helper-paths', 'returns': ['HelperPath'] }
-- 
2.31.1