#pragma once

#include "types.h"

// The kernel log that outlives the kernel.
//
// docs/plan/debugger.md milestone D1. Until this existed, `cprintf` wrote to a
// serial line and a screen and was then gone: a panic's report could be read
// only by whoever was watching at the time, and a triple fault left nothing at
// all. panic.c said so in its own header comment -- *"there is no core dump and
// no log to go back to"* -- and that sentence is what this deletes.
//
// The buffer is a byte ring in a region carved off physical memory *before*
// kalloc or the DMA arena are given anything, at a fixed distance below
// PHYSTOP, so its address is a property of the machine rather than of this
// boot. Nothing allocates it, nothing frees it, and a reboot that leaves DRAM
// alone leaves it intact -- which is what makes the last words of a crashed
// kernel readable from the one that comes after.

#define KLOG_BYTES   (128 * 1024)     // ring plus header
#define KLOG_MAGIC   0x676f4c6bu      // "kLog"
#define KLOG_VERSION 1

// Kept at the head of the region. Everything in it has to survive a reboot, so
// it is all fixed-width and there are no pointers: the only thing that says
// where the data is, is that it follows.
struct klog_hdr {
  uint32 magic;
  uint32 version;
  uint32 size;          // bytes of data[], = KLOG_BYTES - sizeof(struct klog_hdr)
  uint32 boot;          // how many kernels have written here
  uint64 head;          // total bytes ever written; the ring is head mod size
  uint64 mark;          // head as it stood when this boot started
  uint32 sum;           // over the fields above -- see klog.c
  uint32 pad;
  char   data[];
};

void   klog_init(void *base, uint64 bytes);
void   klog_putc(int c);
int    klog_read(uint64 off, char *dst, int n);
uint64 klog_len(void);
uint64 klog_prev_bytes(void);
int    klog_recovered(void);