// The kernel module's tools bundle (novox/hq to-be 42 Phase 1 row 11, issue 746).
//
// Served by the node's runtime over MCP on stdio through the Go SDK (ADR 0188, ADR 0193). It only reads:
// the transparent huge pages the kernel runs with, and which units hold file pages in huge folios, which
// is what a small write to a mapped file costs a whole huge page of writeback for (issue 746).
package main

import (
	"fmt"
	"os"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// binaryName is what the build names this bundle's executable: the manifest's `binary`.
const binaryName = "kernel-tools"

func main() {
	// An empty name serves as the module the runtime names (MESH_SERVED_MODULE): kernel.
	if err := stdio.Serve("", tools(ThisMachine())); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func tools(m *Machine) []stdio.Tool {
	return []stdio.Tool{
		{
			Name: "kernel_huge_pages",
			Description: "Transparent huge pages on this machine: the mode in force (always, madvise or never) and defrag, " +
				"each per-size control with what inherit resolves to, the machine's huge pages by kind (anonymous, " +
				"shared memory, file, file mapped at 2 MiB) from /proc/meminfo, and the units holding the most file " +
				"pages in huge folios (memory.stat file_thp) with their dirty and writeback bytes and the bytes their " +
				"cgroup has written (io.stat, the most any one device saw). A unit with file_thp that writes far more " +
				"than its files grow is paying a whole huge page of writeback per small write (novox/hq issue 746). " +
				"Replaces cat /sys/kernel/mm/transparent_hugepage/enabled, grep Huge /proc/meminfo and reading " +
				"memory.stat by hand. (r)",
			Input: schema(map[string]any{
				"units": map[string]any{"type": "integer", "description": "how many units to name, the most file_thp first (default 10, 0 for none, at most 100)"},
			}),
			Run: func(args map[string]any) (any, error) {
				n, err := whole(args, "units", 10, 0, 100)
				if err != nil {
					return nil, err
				}
				return m.HugePages(n)
			},
		},
	}
}