x15/kern/mbuf.c

/*
 * Copyright (c) 2018-2019 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Upstream site with license notes :
 * http://git.sceen.net/rbraun/librbraun.git/
 */

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

#include <kern/macros.h>
#include <kern/mbuf.h>

/*
 * Message header.
 *
 * The size denotes the size of the data, without the header.
 */
union mbuf_hdr
{
  uint8_t size1;
  uint16_t size2;
  uint32_t size4;
#ifdef __LP64__
  uint64_t size8;
#endif
};

static size_t
mbuf_compute_hdr_size (unsigned int order)
{
  return (order / CHAR_BIT);
}

static void*
mbuf_hdr_get_msg_size_addr (union mbuf_hdr *hdr, unsigned int order)
{
  switch (order)
    {
      case 8:
        return (&hdr->size1);
      case 16:
        return (&hdr->size2);
      default:
#ifdef __LP64__
        return (&hdr->size8);
      case 32:
#endif
        return (&hdr->size4);
    }
}

static size_t
mbuf_hdr_get_msg_size (const union mbuf_hdr *hdr, unsigned int order)
{
  switch (order)
    {
      case 8:
        return (hdr->size1);
      case 16:
        return (hdr->size2);
      default:
#ifdef __LP64__
        return (hdr->size8);
      case 32:
#endif
        return (hdr->size4);
    }
}

static void
mbuf_hdr_init (union mbuf_hdr *hdr, unsigned int order, size_t size)
{
  switch (order)
    {
      case 8:
        assert (size <= UINT8_MAX);
        hdr->size1 = size;
        break;
      case 16:
        assert (size <= UINT16_MAX);
        hdr->size2 = size;
        break;
      default:
#ifdef __LP64__
        hdr->size8 = size;
        break;
      case 32:
        assert (size <= UINT32_MAX);
#endif
        hdr->size4 = size;
    }
}

static size_t
mbuf_hdr_get_total_msg_size (const union mbuf_hdr *hdr, unsigned int order)
{
  return (mbuf_compute_hdr_size (order) + mbuf_hdr_get_msg_size (hdr, order));
}

static unsigned int
mbuf_compute_order (size_t max_msg_size)
{
  assert (max_msg_size);
  unsigned int order = (sizeof (max_msg_size) * CHAR_BIT) -
                       __builtin_clzl (max_msg_size);
  return (P2ROUND (order, CHAR_BIT));
}

void
mbuf_init (struct mbuf *mbuf, void *buf, size_t capacity, size_t max_msg_size)
{
  cbuf_init (&mbuf->cbuf, buf, capacity);
  mbuf->max_msg_size = max_msg_size;
  mbuf->order = mbuf_compute_order (max_msg_size);
}

void
mbuf_clear (struct mbuf *mbuf)
{
  return (cbuf_clear (&mbuf->cbuf));
}

static void
mbuf_clear_old_msgs (struct mbuf *mbuf, size_t total_size)
{
  union mbuf_hdr hdr;

  size_t hdr_size = mbuf_compute_hdr_size (mbuf->order);
  void *msg_size_addr = mbuf_hdr_get_msg_size_addr (&hdr, mbuf->order);

  do
    {
      size_t size = hdr_size;
      int error = cbuf_pop (&mbuf->cbuf, msg_size_addr, &size);
      assert (! error);

      if (! size)
        break;

      size_t msg_size = mbuf_hdr_get_msg_size (&hdr, mbuf->order);
      size = msg_size;
      error = cbuf_pop (&mbuf->cbuf, NULL, &size);
      assert (!error && size == msg_size);
    }
  while (cbuf_avail_size (&mbuf->cbuf) < total_size);
}

int
mbuf_push (struct mbuf *mbuf, const void *buf, size_t size, bool erase)
{
  if (size > mbuf->max_msg_size)
    return (EINVAL);

  union mbuf_hdr hdr;
  mbuf_hdr_init (&hdr, mbuf->order, size);

  size_t total_size = mbuf_hdr_get_total_msg_size (&hdr, mbuf->order);

  if (total_size > cbuf_avail_size (&mbuf->cbuf))
    {
      if (!erase || total_size > cbuf_capacity (&mbuf->cbuf))
        return (EMSGSIZE);

      mbuf_clear_old_msgs (mbuf, total_size);
    }

  size_t hdr_size = mbuf_compute_hdr_size (mbuf->order);
  void *msg_size_addr = mbuf_hdr_get_msg_size_addr (&hdr, mbuf->order);

  int error = cbuf_push (&mbuf->cbuf, msg_size_addr, hdr_size, erase);
  assert (! error);
  error = cbuf_push (&mbuf->cbuf, buf, size, erase);
  assert (! error);

  return (0);
}

int
mbuf_pop (struct mbuf *mbuf, void *buf, size_t *sizep)
{
  size_t start = cbuf_start (&mbuf->cbuf);
  int error = mbuf_read (mbuf, &start, buf, sizep);

  if (! error)
    cbuf_set_start (&mbuf->cbuf, start);

  return (error);
}

int
mbuf_read (const struct mbuf *mbuf, size_t *indexp, void *buf, size_t *sizep)
{
  union mbuf_hdr hdr;
  size_t hdr_size = mbuf_compute_hdr_size (mbuf->order);
  void *msg_size_addr = mbuf_hdr_get_msg_size_addr (&hdr, mbuf->order);

  size_t size = hdr_size;
  int error = cbuf_read (&mbuf->cbuf, *indexp, msg_size_addr, &size);

  if (error)
    return (error);
  else if (size == 0)
    return (EAGAIN);

  assert (size == hdr_size);

  size_t msg_size = mbuf_hdr_get_msg_size (&hdr, mbuf->order);

  if (msg_size > *sizep)
    {
      error = EMSGSIZE;
      goto out;
    }

  size = msg_size;
  error = cbuf_read (&mbuf->cbuf, *indexp + hdr_size, buf, &size);

  if (error)
    goto out;

  assert (size == msg_size);
  *indexp += hdr_size + size;

out:
  *sizep = msg_size;
  return (error);
}