Examples

• Simple heap memory management
• Dynamic grow-only heap management

Simple heap memory management

// L4/L4Env includes
#include <l4/slab/slab.h>
#include <l4/dm_mem/dm_mem.h>
#include <l4/env/errno.h>

#define OBJ_SIZE 64

// grow callback
static void * 
__grow_simple(l4slab_cache_t * cache, void ** data)
{
  void * page;

  // allocate and map page
  page = l4dm_mem_allocate(L4_PAGESIZE,L4RM_MAP | L4RM_LOG2_ALIGNED);
  if (page == NULL)
    Error("__grow_simple: page allocation failed!\n");

  return page;
}

// release callback 
static void
__release_simple(l4slab_cache_t * cache, void * page, void * data)
{
  // free page
  l4dm_mem_release(page);
}

// Main
int
main(void)
{
  l4slab_cache_t slab;
  int ret;
  void * objp;

  // initialize slab
  ret = l4slab_cache_init(&slab,OBJ_SIZE,0,__grow_simple,__release_simple);
  if (ret < 0)
    {
      Error("slab cache initializstion failed: %s (%d)\n",
      l4env_errstr(ret),ret);
      return -1;
    }

  // allocate object
  objp = l4slab_alloc(&slab);

  // do something

  // release object
  l4slab_free(&slab,objp);
  
  // destroy slab
  l4slab_destroy(&slab);

  // done
  return 0;
}

Grow-only heap

This is an a bit more advanced example of how to build a grow-only heap for a slab cache. It avoids to create a new dataspace / vm-region for each page added to the slab cache, instead it resizes the heap dataspace to add a new page to the slab cache.

// L4/L4Env includes
#include <l4/slab/slab.h>
#include <l4/dm_mem/dm_mem.h>
#include <l4/l4rm/l4rm.h>
#include <l4/env/errno.h>
#include <l4/util/macros.h>

#define MAX_HEAP_SIZE  (64 * 1024)
#define INIT_HEAP_SIZE (16 * 1024)
 
l4dm_dataspace_t heap_ds;
l4_addr_t        heap_addr;
l4_size_t        heap_cur_size;

// grow callback
static void *
__grow(l4slab_cache_t * cache, void ** data)
{
  l4_addr_t addr;
  l4_size_t new_size; 
  int ret;

  if ((heap_cur_size + L4_PAGESIZE) > MAX_HEAP_SIZE)
    {
      printf("__grow: heap overflow!\n");
      return NULL;
    }

  // resize dataspace
  addr = heap_addr + heap_cur_size;
  new_size = heap_cur_size + L4_PAGESIZE;

  ret = l4dm_mem_resize(&heap_ds,new_size);
  if (ret < 0)
    {
      printf("__grow: resize heap dataspace failed: %s (%d)\n",
       l4env_errstr(ret),ret);
      return NULL;
    }
  heap_cur_size = new_size;

  // done
  return (void *)addr;
}

// Main
int
main(void)
{
  int ret;
  void * heap, * page;
  l4slab_cache_t slab;
  void * objp;

  // allocate heap dataspace
  ret = l4dm_mem_open(L4DM_DEFAULT_DSM, INIT_HEAP_SIZE, L4_PAGESIZE, 0,
          "Heap", &heap_ds);
  if (ret < 0)
    {
      Error("heap allocation failed: %s (%d)\n",l4env_errstr(ret),ret);
      return -1;
    }

  // attach heap dataspace, already reserve the whole vm area 
  ret = l4rm_attach(&heap_ds, MAX_HEAP_SIZE, 0, L4DM_RW, &heap);
  if (ret < 0)
    {
      Error("attach heap dataspace failed: %s (%d)\n",l4env_errstr(ret),ret);
      l4dm_close(&heap_ds);
      return -1;
    }
  heap_addr = (l4_addr_t)heap;
  heap_cur_size = INIT_HEAP_SIZE;

  // setup slab cache, no release callback
  ret = l4slab_cache_init(&slab,OBJ_SIZE,0,__grow,NULL);
  if (ret < 0)
    {
      Error("slab cache initialization failed: %s (%d)\n",
      l4env_errstr(ret),ret);
      return -1;
    }

  // add initial pages to the slab cache 
  page = heap;
  while (page < (heap + INIT_HEAP_SIZE))
    {
      l4slab_add_page(&slab,page,NULL);
      page += L4_PAGESIZE;
    }

  // allocate objects
  objp = l4slab_alloc(&slab);
 
  // do something 

  // release object
  l4slab_free(&slab,objp);
  
  // destroy slab
  l4slab_destroy(&slab);

  // release heap memory 
  l4rm_detach((void *)heap_addr);
  l4dm_close(&heap_ds);
}