/*
  ISC License

  Copyright (c) 2022, Antonio SJ Musumeci <trapexit@spawn.link>
  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#include "fuse_msgbuf.hpp"

#include "fuse.h"
#include "fuse_kernel.h"

#include <unistd.h>

#include <cassert>
#include <atomic>
#include <cstdlib>
#include <mutex>
#include <vector>


static u32 g_PAGESIZE = 0;
static u64 g_BUFSIZE  = 0;

static std::atomic<std::uint_fast64_t> g_MSGBUF_ALLOC_COUNT = 0;

static std::mutex g_MUTEX;
static std::vector<fuse_msgbuf_t*> g_MSGBUF_STACK;

u64
msgbuf_get_bufsize()
{
  return g_BUFSIZE;
}

u32
msgbuf_get_pagesize()
{
  return g_PAGESIZE;
}

// +1 page so that it is used for the "header" of the allocation as
// well as to allow for offseting for write requests to be page
// aligned. +1 again for fuse header as the max_pages value is for the
// body.
void
msgbuf_set_bufsize(const u64 size_in_pages_)
{
  g_BUFSIZE = ((size_in_pages_ + 2) * g_PAGESIZE);
}

static
void
_msgbuf_page_align(fuse_msgbuf_t *msgbuf_)
{
  msgbuf_->mem   = (char*)msgbuf_;
  msgbuf_->mem  += g_PAGESIZE;
  msgbuf_->size  = (g_BUFSIZE - g_PAGESIZE);
}

static
void
_msgbuf_write_align(fuse_msgbuf_t *msgbuf_)
{
  msgbuf_->mem   = (char*)msgbuf_;
  msgbuf_->mem  += g_PAGESIZE;
  msgbuf_->mem  -= sizeof(struct fuse_in_header);
  msgbuf_->mem  -= sizeof(struct fuse_write_in);
  msgbuf_->size  = (g_BUFSIZE - g_PAGESIZE);
}

static
__attribute__((constructor))
void
_msgbuf_constructor()
{
  long pagesize = sysconf(_SC_PAGESIZE);

  assert(pagesize > 0);
  g_PAGESIZE = pagesize;

  // Ensure fuse headers fit within a single page for O_DIRECT alignment
  assert((sizeof(struct fuse_in_header) + sizeof(struct fuse_write_in))
         < g_PAGESIZE);

  msgbuf_set_bufsize(FUSE_DEFAULT_MAX_MAX_PAGES);
}

static
__attribute__((destructor))
void
_msgbuf_destructor()
{
  msgbuf_gc();
}

static
void*
_page_aligned_malloc(const u64 size_in_bytes_)
{
  int rv;
  void *buf = NULL;

  rv = posix_memalign(&buf,g_PAGESIZE,size_in_bytes_);
  if(rv != 0)
    return NULL;

  return buf;
}

typedef void (*msgbuf_setup_func_t)(fuse_msgbuf_t*);

static
fuse_msgbuf_t*
_msgbuf_alloc(msgbuf_setup_func_t setup_func_)
{
  fuse_msgbuf_t *msgbuf;

  g_MUTEX.lock();
  if(g_MSGBUF_STACK.empty())
    {
      g_MUTEX.unlock();

      msgbuf = (fuse_msgbuf_t*)_page_aligned_malloc(g_BUFSIZE);
      if(msgbuf == NULL)
        return NULL;

      g_MSGBUF_ALLOC_COUNT.fetch_add(1,std::memory_order_relaxed);
    }
  else
    {
      msgbuf = g_MSGBUF_STACK.back();
      g_MSGBUF_STACK.pop_back();
      g_MUTEX.unlock();
    }

  setup_func_(msgbuf);

  return msgbuf;
}

// Offset the memory so write request payload will be placed on page
// boundry so O_DIRECT can work. No impact on other message types
// except for `read` which will require using `msgbuf_page_align`.
fuse_msgbuf_t*
msgbuf_alloc()
{
  return _msgbuf_alloc(_msgbuf_write_align);
}

fuse_msgbuf_t*
msgbuf_alloc_page_aligned()
{
  return _msgbuf_alloc(_msgbuf_page_align);
}

static
void
msgbuf_destroy(fuse_msgbuf_t *msgbuf_)
{
  free(msgbuf_);
}

void
msgbuf_free(fuse_msgbuf_t *msgbuf_)
{
  bool destroy;

  {
    std::lock_guard<std::mutex> lck(g_MUTEX);

    destroy = (msgbuf_->size != (g_BUFSIZE - g_PAGESIZE));
    if(!destroy)
      g_MSGBUF_STACK.emplace_back(msgbuf_);
  }

  if(destroy)
    {
      msgbuf_destroy(msgbuf_);
      g_MSGBUF_ALLOC_COUNT.fetch_sub(1,std::memory_order_relaxed);
    }
}

u64
msgbuf_alloc_count()
{
  return g_MSGBUF_ALLOC_COUNT;
}

u64
msgbuf_avail_count()
{
  std::lock_guard<std::mutex> lck(g_MUTEX);

  return g_MSGBUF_STACK.size();
}

void
msgbuf_gc_10percent()
{
  std::vector<fuse_msgbuf_t*> togc;

  {
    std::size_t size;
    std::size_t ten_percent;

    std::lock_guard<std::mutex> lck(g_MUTEX);

    size        = g_MSGBUF_STACK.size();
    ten_percent = (size / 10);

    for(std::size_t i = 0; i < ten_percent; i++)
      {
        togc.push_back(g_MSGBUF_STACK.back());
        g_MSGBUF_STACK.pop_back();
      }
  }

  for(auto msgbuf : togc)
    {
      msgbuf_destroy(msgbuf);
      g_MSGBUF_ALLOC_COUNT.fetch_sub(1,std::memory_order_relaxed);
    }
}

void
msgbuf_gc()
{
  std::vector<fuse_msgbuf_t*> oldstack;

  {
    std::lock_guard<std::mutex> lck(g_MUTEX);
    oldstack.swap(g_MSGBUF_STACK);
  }

  for(auto msgbuf: oldstack)
    {
      msgbuf_destroy(msgbuf);
      g_MSGBUF_ALLOC_COUNT.fetch_sub(1,std::memory_order_relaxed);
    }
}