// SPDX-License-Identifier: Apache-2.0
//
// Counters for the filesystem and block paths, read through /proc/fsstat.
//
// These exist because "the system feels slow" is not a bug report anyone can
// act on, and every guess about where the time goes in a filesystem is wrong
// until it is measured. `ls /bin` taking three seconds could be the directory
// walk, the tree descents, the copy path, or the disk -- and those four call
// for completely different fixes.
//
// Deliberately plain `uint64` with no locking. A counter that is off by one
// because two CPUs raced tells you the same thing as one that is exact, and a
// lock here would change the very timings it is meant to report.
#pragma once

struct fsstat {
  // Buffer cache. `bread_miss` is the one that matters: a miss is a real
  // transfer, a hit is a memcpy.
  uint64 bread_calls;
  uint64 bread_miss;
  uint64 bget_evict_dirty;   // had to write a buffer out to make room

  // Actual device transfers, and the cycles spent inside them.
  uint64 disk_reads;
  uint64 disk_writes;
  uint64 disk_cycles;

  // The VFS read path: one call is one read(2) reaching a SchFS file.
  uint64 read_calls;
  uint64 read_bytes;
  uint64 read_cycles;

  // Directory listing.
  uint64 getdents_calls;
  uint64 getdents_cycles;
  uint64 getdents_walked;    // entries stepped over, including ones re-walked

  // B-tree descents from the root, and the block reads they cost.
  uint64 descents;

  // exec(2), which on this system means reading an 800 KB multicall binary.
  uint64 exec_calls;
  uint64 exec_cycles;
};

extern struct fsstat fsstat;