talloc.c

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/* 
   Samba Unix SMB/CIFS implementation.

   Samba trivial allocation library - new interface

   NOTE: Please read talloc_guide.txt for full documentation

   Copyright (C) Andrew Tridgell 2004
   Copyright (C) Stefan Metzmacher 2006
   
     ** NOTE! The following LGPL license applies to the talloc
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

/*
  inspired by http://swapped.cc/halloc/
*/

#ifdef _SAMBA_BUILD_
#include "version.h"
#if (SAMBA_VERSION_MAJOR<4)
#include "includes.h"
/* This is to circumvent SAMBA3's paranoid malloc checker. Here in this file
 * we trust ourselves... */
#ifdef malloc
#undef malloc
#endif
#ifdef realloc
#undef realloc
#endif
#define _TALLOC_SAMBA3
#endif /* (SAMBA_VERSION_MAJOR<4) */
#endif /* _SAMBA_BUILD_ */

#ifndef _TALLOC_SAMBA3
#include "replace.h"
#include "talloc.h"
#endif /* not _TALLOC_SAMBA3 */

/* use this to force every realloc to change the pointer, to stress test
   code that might not cope */
#define ALWAYS_REALLOC 0


#define MAX_TALLOC_SIZE 0x10000000
#define TALLOC_MAGIC 0xe814ec70
#define TALLOC_FLAG_FREE 0x01
#define TALLOC_FLAG_LOOP 0x02
#define TALLOC_FLAG_POOL 0x04		/* This is a talloc pool */
#define TALLOC_FLAG_POOLMEM 0x08	/* This is allocated in a pool */
#define TALLOC_MAGIC_REFERENCE ((const char *)1)

/* by default we abort when given a bad pointer (such as when talloc_free() is called 
   on a pointer that came from malloc() */
#ifndef TALLOC_ABORT
#define TALLOC_ABORT(reason) abort()
#endif

#ifndef discard_const_p
#if defined(__intptr_t_defined) || defined(HAVE_INTPTR_T)
# define discard_const_p(type, ptr) ((type *)((intptr_t)(ptr)))
#else
# define discard_const_p(type, ptr) ((type *)(ptr))
#endif
#endif

/* these macros gain us a few percent of speed on gcc */
#if (__GNUC__ >= 3)
/* the strange !! is to ensure that __builtin_expect() takes either 0 or 1
   as its first argument */
#define likely(x)   __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#else
#define likely(x) x
#define unlikely(x) x
#endif

/* this null_context is only used if talloc_enable_leak_report() or
   talloc_enable_leak_report_full() is called, otherwise it remains
   NULL
*/
static void *null_context;
static void *autofree_context;

struct talloc_reference_handle {
	struct talloc_reference_handle *next, *prev;
	void *ptr;
};

typedef int (*talloc_destructor_t)(void *);

struct talloc_chunk {
	struct talloc_chunk *next, *prev;
	struct talloc_chunk *parent, *child;
	struct talloc_reference_handle *refs;
	talloc_destructor_t destructor;
	const char *name;
	size_t size;
	unsigned flags;

	/*
	 * "pool" has dual use:
	 *
	 * For the talloc pool itself (i.e. TALLOC_FLAG_POOL is set), "pool"
	 * marks the end of the currently allocated area.
	 *
	 * For members of the pool (i.e. TALLOC_FLAG_POOLMEM is set), "pool"
	 * is a pointer to the struct talloc_chunk of the pool that it was
	 * allocated from. This way children can quickly find the pool to chew
	 * from.
	 */
	void *pool;
};

/* 16 byte alignment seems to keep everyone happy */
#define TC_HDR_SIZE ((sizeof(struct talloc_chunk)+15)&~15)
#define TC_PTR_FROM_CHUNK(tc) ((void *)(TC_HDR_SIZE + (char*)tc))

static void talloc_abort_double_free(void)
{
	TALLOC_ABORT("Bad talloc magic value - double free"); 
}

static void talloc_abort_unknown_value(void)
{
	TALLOC_ABORT("Bad talloc magic value - unknown value"); 
}

/* panic if we get a bad magic value */
static inline struct talloc_chunk *talloc_chunk_from_ptr(const void *ptr)
{
	const char *pp = (const char *)ptr;
	struct talloc_chunk *tc = discard_const_p(struct talloc_chunk, pp - TC_HDR_SIZE);
	if (unlikely((tc->flags & (TALLOC_FLAG_FREE | ~0xF)) != TALLOC_MAGIC)) { 
		if (tc->flags & TALLOC_FLAG_FREE) {
			talloc_abort_double_free();
		} else {
			talloc_abort_unknown_value();
		}
	}
	return tc;
}

/* hook into the front of the list */
#define _TLIST_ADD(list, p) \
do { \
        if (!(list)) { \
		(list) = (p); \
		(p)->next = (p)->prev = NULL; \
	} else { \
		(list)->prev = (p); \
		(p)->next = (list); \
		(p)->prev = NULL; \
		(list) = (p); \
	}\
} while (0)

/* remove an element from a list - element doesn't have to be in list. */
#define _TLIST_REMOVE(list, p) \
do { \
	if ((p) == (list)) { \
		(list) = (p)->next; \
		if (list) (list)->prev = NULL; \
	} else { \
		if ((p)->prev) (p)->prev->next = (p)->next; \
		if ((p)->next) (p)->next->prev = (p)->prev; \
	} \
	if ((p) && ((p) != (list))) (p)->next = (p)->prev = NULL; \
} while (0)


/*
  return the parent chunk of a pointer
*/
static inline struct talloc_chunk *talloc_parent_chunk(const void *ptr)
{
	struct talloc_chunk *tc;

	if (unlikely(ptr == NULL)) {
		return NULL;
	}

	tc = talloc_chunk_from_ptr(ptr);
	while (tc->prev) tc=tc->prev;

	return tc->parent;
}

void *talloc_parent(const void *ptr)
{
	struct talloc_chunk *tc = talloc_parent_chunk(ptr);
	return tc? TC_PTR_FROM_CHUNK(tc) : NULL;
}

/*
  find parents name
*/
const char *talloc_parent_name(const void *ptr)
{
	struct talloc_chunk *tc = talloc_parent_chunk(ptr);
	return tc? tc->name : NULL;
}

/*
  A pool carries an in-pool object count count in the first 16 bytes.
  bytes. This is done to support talloc_steal() to a parent outside of the
  pool. The count includes the pool itself, so a talloc_free() on a pool will
  only destroy the pool if the count has dropped to zero. A talloc_free() of a
  pool member will reduce the count, and eventually also call free(3) on the
  pool memory.

  The object count is not put into "struct talloc_chunk" because it is only
  relevant for talloc pools and the alignment to 16 bytes would increase the
  memory footprint of each talloc chunk by those 16 bytes.
*/

#define TALLOC_POOL_HDR_SIZE 16

static unsigned int *talloc_pool_objectcount(struct talloc_chunk *tc)
{
	return (unsigned int *)((char *)tc + sizeof(struct talloc_chunk));
}

/*
  Allocate from a pool
*/

static struct talloc_chunk *talloc_alloc_pool(struct talloc_chunk *parent,
					      size_t size)
{
	struct talloc_chunk *pool_ctx = NULL;
	size_t space_left;
	struct talloc_chunk *result;
	size_t chunk_size;

	if (parent == NULL) {
		return NULL;
	}

	if (parent->flags & TALLOC_FLAG_POOL) {
		pool_ctx = parent;
	}
	else if (parent->flags & TALLOC_FLAG_POOLMEM) {
		pool_ctx = (struct talloc_chunk *)parent->pool;
	}

	if (pool_ctx == NULL) {
		return NULL;
	}

	space_left = ((char *)pool_ctx + TC_HDR_SIZE + pool_ctx->size)
		- ((char *)pool_ctx->pool);

	/*
	 * Align size to 16 bytes
	 */
	chunk_size = ((size + 15) & ~15);

	if (space_left < chunk_size) {
		return NULL;
	}

	result = (struct talloc_chunk *)pool_ctx->pool;

#if defined(DEVELOPER) && defined(VALGRIND_MAKE_MEM_UNDEFINED)
	VALGRIND_MAKE_MEM_UNDEFINED(result, size);
#endif

	pool_ctx->pool = (void *)((char *)result + chunk_size);

	result->flags = TALLOC_MAGIC | TALLOC_FLAG_POOLMEM;
	result->pool = pool_ctx;

	*talloc_pool_objectcount(pool_ctx) += 1;

	return result;
}

/* 
   Allocate a bit of memory as a child of an existing pointer
*/
static inline void *__talloc(const void *context, size_t size)
{
	struct talloc_chunk *tc = NULL;

	if (unlikely(context == NULL)) {
		context = null_context;
	}

	if (unlikely(size >= MAX_TALLOC_SIZE)) {
		return NULL;
	}

	if (context != NULL) {
		tc = talloc_alloc_pool(talloc_chunk_from_ptr(context),
				       TC_HDR_SIZE+size);
	}

	if (tc == NULL) {
		tc = (struct talloc_chunk *)malloc(TC_HDR_SIZE+size);
		if (unlikely(tc == NULL)) return NULL;
		tc->flags = TALLOC_MAGIC;
		tc->pool  = NULL;
	}

	tc->size = size;
	tc->destructor = NULL;
	tc->child = NULL;
	tc->name = NULL;
	tc->refs = NULL;

	if (likely(context)) {
		struct talloc_chunk *parent = talloc_chunk_from_ptr(context);

		if (parent->child) {
			parent->child->parent = NULL;
			tc->next = parent->child;
			tc->next->prev = tc;
		} else {
			tc->next = NULL;
		}
		tc->parent = parent;
		tc->prev = NULL;
		parent->child = tc;
	} else {
		tc->next = tc->prev = tc->parent = NULL;
	}

	return TC_PTR_FROM_CHUNK(tc);
}

/*
 * Create a talloc pool
 */

void *talloc_pool(const void *context, size_t size)
{
	void *result = __talloc(context, size + TALLOC_POOL_HDR_SIZE);
	struct talloc_chunk *tc;

	if (unlikely(result == NULL)) {
		return NULL;
	}

	tc = talloc_chunk_from_ptr(result);

	tc->flags |= TALLOC_FLAG_POOL;
	tc->pool = (char *)result + TALLOC_POOL_HDR_SIZE;

	*talloc_pool_objectcount(tc) = 1;

#if defined(DEVELOPER) && defined(VALGRIND_MAKE_MEM_NOACCESS)
	VALGRIND_MAKE_MEM_NOACCESS(tc->pool, size);
#endif

	return result;
}

/*
  setup a destructor to be called on free of a pointer
  the destructor should return 0 on success, or -1 on failure.
  if the destructor fails then the free is failed, and the memory can
  be continued to be used
*/
void _talloc_set_destructor(const void *ptr, int (*destructor)(void *))
{
	struct talloc_chunk *tc = talloc_chunk_from_ptr(ptr);
	tc->destructor = destructor;
}

/*
  increase the reference count on a piece of memory. 
*/
int talloc_increase_ref_count(const void *ptr)
{
	if (unlikely(!talloc_reference(null_context, ptr))) {
		return -1;
	}
	return 0;
}

/*
  helper for talloc_reference()

  this is referenced by a function pointer and should not be inline
*/
static int talloc_reference_destructor(struct talloc_reference_handle *handle)
{
	struct talloc_chunk *ptr_tc = talloc_chunk_from_ptr(handle->ptr);
	_TLIST_REMOVE(ptr_tc->refs, handle);
	return 0;
}

/*
   more efficient way to add a name to a pointer - the name must point to a 
   true string constant
*/
static inline void _talloc_set_name_const(const void *ptr, const char *name)
{
	struct talloc_chunk *tc = talloc_chunk_from_ptr(ptr);
	tc->name = name;
}

/*
  internal talloc_named_const()
*/
static inline void *_talloc_named_const(const void *context, size_t size, const char *name)
{
	void *ptr;

	ptr = __talloc(context, size);
	if (unlikely(ptr == NULL)) {
		return NULL;
	}

	_talloc_set_name_const(ptr, name);

	return ptr;
}

/*
  make a secondary reference to a pointer, hanging off the given context.
  the pointer remains valid until both the original caller and this given
  context are freed.
  
  the major use for this is when two different structures need to reference the 
  same underlying data, and you want to be able to free the two instances separately,
  and in either order
*/
void *_talloc_reference(const void *context, const void *ptr)
{
	struct talloc_chunk *tc;
	struct talloc_reference_handle *handle;
	if (unlikely(ptr == NULL)) return NULL;

	tc = talloc_chunk_from_ptr(ptr);
	handle = (struct talloc_reference_handle *)_talloc_named_const(context,
						   sizeof(struct talloc_reference_handle),
						   TALLOC_MAGIC_REFERENCE);
	if (unlikely(handle == NULL)) return NULL;

	/* note that we hang the destructor off the handle, not the
	   main context as that allows the caller to still setup their
	   own destructor on the context if they want to */
	talloc_set_destructor(handle, talloc_reference_destructor);
	handle->ptr = discard_const_p(void, ptr);
	_TLIST_ADD(tc->refs, handle);
	return handle->ptr;
}


/* 
   internal talloc_free call
*/
static inline int _talloc_free(void *ptr)
{
	struct talloc_chunk *tc;

	if (unlikely(ptr == NULL)) {
		return -1;
	}

	tc = talloc_chunk_from_ptr(ptr);

	if (unlikely(tc->refs)) {
		int is_child;
		/* check this is a reference from a child or grantchild
		 * back to it's parent or grantparent
		 *
		 * in that case we need to remove the reference and
		 * call another instance of talloc_free() on the current
		 * pointer.
		 */
		is_child = talloc_is_parent(tc->refs, ptr);
		_talloc_free(tc->refs);
		if (is_child) {
			return _talloc_free(ptr);
		}
		return -1;
	}

	if (unlikely(tc->flags & TALLOC_FLAG_LOOP)) {
		/* we have a free loop - stop looping */
		return 0;
	}

	if (unlikely(tc->destructor)) {
		talloc_destructor_t d = tc->destructor;
		if (d == (talloc_destructor_t)-1) {
			return -1;
		}
		tc->destructor = (talloc_destructor_t)-1;
		if (d(ptr) == -1) {
			tc->destructor = d;
			return -1;
		}
		tc->destructor = NULL;
	}

	if (tc->parent) {
		_TLIST_REMOVE(tc->parent->child, tc);
		if (tc->parent->child) {
			tc->parent->child->parent = tc->parent;
		}
	} else {
		if (tc->prev) tc->prev->next = tc->next;
		if (tc->next) tc->next->prev = tc->prev;
	}

	tc->flags |= TALLOC_FLAG_LOOP;

	while (tc->child) {
		/* we need to work out who will own an abandoned child
		   if it cannot be freed. In priority order, the first
		   choice is owner of any remaining reference to this
		   pointer, the second choice is our parent, and the
		   final choice is the null context. */
		void *child = TC_PTR_FROM_CHUNK(tc->child);
		const void *new_parent = null_context;
		if (unlikely(tc->child->refs)) {
			struct talloc_chunk *p = talloc_parent_chunk(tc->child->refs);
			if (p) new_parent = TC_PTR_FROM_CHUNK(p);
		}
		if (unlikely(_talloc_free(child) == -1)) {
			if (new_parent == null_context) {
				struct talloc_chunk *p = talloc_parent_chunk(ptr);
				if (p) new_parent = TC_PTR_FROM_CHUNK(p);
			}
			talloc_steal(new_parent, child);
		}
	}

	tc->flags |= TALLOC_FLAG_FREE;

	if (tc->flags & (TALLOC_FLAG_POOL|TALLOC_FLAG_POOLMEM)) {
		struct talloc_chunk *pool;
		unsigned int *pool_object_count;

		pool = (tc->flags & TALLOC_FLAG_POOL)
			? tc : (struct talloc_chunk *)tc->pool;

		pool_object_count = talloc_pool_objectcount(pool);

		if (*pool_object_count == 0) {
			TALLOC_ABORT("Pool object count zero!");
		}

		*pool_object_count -= 1;

		if (*pool_object_count == 0) {
			free(pool);
		}
	}
	else {
		free(tc);
	}
	return 0;
}

/* 
   move a lump of memory from one talloc context to another return the