tools: ynltool: create skeleton for the C command

Based on past discussions it seems like integration of YNL into
iproute2 is unlikely. YNL itself is not great as a C library,
since it has no backward compat (we routinely change types).

Most of the operations can be performed with the generic Python
CLI directly. There is, however, a handful of operations where
summarization of kernel output is very useful (mostly related
to stats: page-pool, qstat).

Create a command (inspired by bpftool, I think it stood the test
of time reasonably well) to be able to plug the subcommands into.

Link: https://lore.kernel.org/1754895902-8790-1-git-send-email-ernis@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20251107162227.980672-2-kuba@kernel.org
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/tools/net/ynl/ynltool/json_writer.h b/tools/net/ynl/ynltool/json_writer.h
new file mode 100644
index 000000000000..0f1e63c88f6a
--- /dev/null
+++ b/tools/net/ynl/ynltool/json_writer.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
+/*
+ * Simple streaming JSON writer
+ *
+ * This takes care of the annoying bits of JSON syntax like the commas
+ * after elements
+ *
+ * Authors:	Stephen Hemminger <stephen@networkplumber.org>
+ */
+
+#ifndef _JSON_WRITER_H_
+#define _JSON_WRITER_H_
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include <stdio.h>
+
+/* Opaque class structure */
+typedef struct json_writer json_writer_t;
+
+/* Create a new JSON stream */
+json_writer_t *jsonw_new(FILE *f);
+/* End output to JSON stream */
+void jsonw_destroy(json_writer_t **self_p);
+
+/* Cause output to have pretty whitespace */
+void jsonw_pretty(json_writer_t *self, bool on);
+
+/* Reset separator to create new JSON */
+void jsonw_reset(json_writer_t *self);
+
+/* Add property name */
+void jsonw_name(json_writer_t *self, const char *name);
+
+/* Add value  */
+void __attribute__((format(printf, 2, 0))) jsonw_vprintf_enquote(json_writer_t *self,
+								 const char *fmt,
+								 va_list ap);
+void __attribute__((format(printf, 2, 3))) jsonw_printf(json_writer_t *self,
+							const char *fmt, ...);
+void jsonw_string(json_writer_t *self, const char *value);
+void jsonw_bool(json_writer_t *self, bool value);
+void jsonw_float(json_writer_t *self, double number);
+void jsonw_float_fmt(json_writer_t *self, const char *fmt, double num);
+void jsonw_uint(json_writer_t *self, uint64_t number);
+void jsonw_hu(json_writer_t *self, unsigned short number);
+void jsonw_int(json_writer_t *self, int64_t number);
+void jsonw_null(json_writer_t *self);
+void jsonw_lluint(json_writer_t *self, unsigned long long int num);
+
+/* Useful Combinations of name and value */
+void jsonw_string_field(json_writer_t *self, const char *prop, const char *val);
+void jsonw_bool_field(json_writer_t *self, const char *prop, bool value);
+void jsonw_float_field(json_writer_t *self, const char *prop, double num);
+void jsonw_uint_field(json_writer_t *self, const char *prop, uint64_t num);
+void jsonw_hu_field(json_writer_t *self, const char *prop, unsigned short num);
+void jsonw_int_field(json_writer_t *self, const char *prop, int64_t num);
+void jsonw_null_field(json_writer_t *self, const char *prop);
+void jsonw_lluint_field(json_writer_t *self, const char *prop,
+			unsigned long long int num);
+void jsonw_float_field_fmt(json_writer_t *self, const char *prop,
+			   const char *fmt, double val);
+
+/* Collections */
+void jsonw_start_object(json_writer_t *self);
+void jsonw_end_object(json_writer_t *self);
+
+void jsonw_start_array(json_writer_t *self);
+void jsonw_end_array(json_writer_t *self);
+
+/* Override default exception handling */
+typedef void (jsonw_err_handler_fn)(const char *);
+
+#endif /* _JSON_WRITER_H_ */