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TALLOC(3)		  System Administration	tools		     TALLOC(3)

NAME
       talloc -	hierarchical reference counted memory pool system with
       destructors

SYNOPSIS
       #include	<talloc.h>

DESCRIPTION
       If you are used to talloc from Samba3 then please read this carefully,
       as talloc has changed a lot.

       The new talloc is a hierarchical, reference counted memory pool system
       with destructors. Quite a mouthful really, but not too bad once you get
       used to it.

       Perhaps the biggest change from Samba3 is that there is no distinction
       between a "talloc context" and a	"talloc	pointer". Any pointer returned
       from talloc() is	itself a valid talloc context. This means you can do
       this:

	       struct foo *X = talloc(mem_ctx, struct foo);
	       X->name = talloc_strdup(X, "foo");

       and the pointer X->name would be	a "child" of the talloc	context	X
       which is	itself a child of mem_ctx. So if you do	talloc_free(mem_ctx)
       then it is all destroyed, whereas if you	do talloc_free(X) then just X
       and X->name are destroyed, and if you do	talloc_free(X->name) then just
       the name	element	of X is	destroyed.

       If you think about this,	then what this effectively gives you is	an
       n-ary tree, where you can free any part of the tree with	talloc_free().

       If you find this	confusing, then	I suggest you run the testsuite
       program to watch	talloc in action. You may also like to add your	own
       tests to	testsuite.c to clarify how some	particular situation is
       handled.

TALLOC API
       The following is	a complete guide to the	talloc API. Read it all	at
       least twice.

   (type *)talloc(const	void *ctx, type);
       The talloc() macro is the core of the talloc library. It	takes a	memory
       ctx and a type, and returns a pointer to	a new area of memory of	the
       given type.

       The returned pointer is itself a	talloc context,	so you can use it as
       the ctx argument	to more	calls to talloc() if you wish.

       The returned pointer is a "child" of the	supplied context. This means
       that if you talloc_free() the ctx then the new child disappears as
       well. Alternatively you can free	just the child.

       The ctx argument	to talloc() can	be NULL, in which case a new top level
       context is created.

   void	*talloc_size(const void	*ctx, size_t size);
       The function talloc_size() should be used when you don't	have a
       convenient type to pass to talloc(). Unlike talloc(), it	is not type
       safe (as	it returns a void *), so you are on your own for type
       checking.

   (typeof(ptr)) talloc_ptrtype(const void *ctx, ptr);
       The talloc_ptrtype() macro should be used when you have a pointer and
       want to allocate	memory to point	at with	this pointer. When compiling
       with gcc	>= 3 it	is typesafe. Note this is a wrapper of talloc_size()
       and talloc_get_name() will return the current location in the source
       file. and not the type.

   int talloc_free(void	*ptr);
       The talloc_free() function frees	a piece	of talloc memory, and all its
       children. You can call talloc_free() on any pointer returned by
       talloc().

       The return value	of talloc_free() indicates success or failure, with 0
       returned	for success and	-1 for failure.	The only possible failure
       condition is if ptr had a destructor attached to	it and the destructor
       returned	-1. See	"talloc_set_destructor()" for details on destructors.

       If this pointer has an additional parent	when talloc_free() is called
       then the	memory is not actually released, but instead the most recently
       established parent is destroyed.	See "talloc_reference()" for details
       on establishing additional parents.

       For more	control	on which parent	is removed, see	"talloc_unlink()".

       talloc_free() operates recursively on its children.

       From the	2.0 version of talloc, as a special case, talloc_free()	is
       refused on pointers that	have more than one parent, as talloc would
       have no way of knowing which parent should be removed. To free a
       pointer that has	more than one parent please use	talloc_unlink().

       To help you find	problems in your code caused by	this behaviour,	if you
       do try and free a pointer with more than	one parent then	the talloc
       logging function	will be	called to give output like this:

		    ERROR: talloc_free with references at some_dir/source/foo.c:123
		     reference at some_dir/source/other.c:325
		     reference at some_dir/source/third.c:121

       Please see the documentation for	talloc_set_log_fn() and
       talloc_set_log_stderr() for more	information on talloc logging
       functions.

   void	*talloc_reference(const	void *ctx, const void *ptr);
       The talloc_reference() function makes ctx an additional parent of ptr.

       The return value	of talloc_reference() is always	the original pointer
       ptr, unless talloc ran out of memory in creating	the reference in which
       case it will return NULL	(each additional reference consumes around 48
       bytes of	memory on intel	x86 platforms).

       If ptr is NULL, then the	function is a no-op, and simply	returns	NULL.

       After creating a	reference you can free it in one of the	following
       ways:

       o   you can talloc_free() any parent of the original pointer. That will
	   reduce the number of	parents	of this	pointer	by 1, and will cause
	   this	pointer	to be freed if it runs out of parents.

       o   you can talloc_free() the pointer itself if it has at maximum one
	   parent. This	behaviour has been changed since the release of
	   version 2.0.	Further	informations in	the description	of
	   "talloc_free".

       For more	control	on which parent	to remove, see "talloc_unlink()".

   int talloc_unlink(const void	*ctx, void *ptr);
       The talloc_unlink() function removes a specific parent from ptr.	The
       ctx passed must either be a context used	in talloc_reference() with
       this pointer, or	must be	a direct parent	of ptr.

       Note that if the	parent has already been	removed	using talloc_free()
       then this function will fail and	will return -1.	Likewise, if ptr is
       NULL, then the function will make no modifications and return -1.

       Usually you can just use	talloc_free() instead of talloc_unlink(), but
       sometimes it is useful to have the additional control on	which parent
       is removed.

   void	talloc_set_destructor(const void *ptr, int (*destructor)(void *));
       The function talloc_set_destructor() sets the destructor	for the
       pointer ptr. A destructor is a function that is called when the memory
       used by a pointer is about to be	released. The destructor receives ptr
       as an argument, and should return 0 for success and -1 for failure.

       The destructor can do anything it wants to, including freeing other
       pieces of memory. A common use for destructors is to clean up operating
       system resources	(such as open file descriptors)	contained in the
       structure the destructor	is placed on.

       You can only place one destructor on a pointer. If you need more	than
       one destructor then you can create a zero-length	child of the pointer
       and place an additional destructor on that.

       To remove a destructor call talloc_set_destructor() with	NULL for the
       destructor.

       If your destructor attempts to talloc_free() the	pointer	that it	is the
       destructor for then talloc_free() will return -1	and the	free will be
       ignored.	This would be a	pointless operation anyway, as the destructor
       is only called when the memory is just about to go away.

   int talloc_increase_ref_count(const void *ptr);
       The talloc_increase_ref_count(ptr) function is exactly equivalent to:

	   talloc_reference(NULL, ptr);

       You can use either syntax, depending on which you think is clearer in
       your code.

       It returns 0 on success and -1 on failure.

   size_t talloc_reference_count(const void *ptr);
       Return the number of references to the pointer.

   void	talloc_set_name(const void *ptr, const char *fmt, ...);
       Each talloc pointer has a "name". The name is used principally for
       debugging purposes, although it is also possible	to set and get the
       name on a pointer in as a way of	"marking" pointers in your code.

       The main	use for	names on pointer is for	"talloc	reports". See
       "talloc_report_depth_cb()", "talloc_report_depth_file()",
       "talloc_report()" "talloc_report()" and "talloc_report_full()" for
       details.	Also see "talloc_enable_leak_report()" and
       "talloc_enable_leak_report_full()".

       The talloc_set_name() function allocates	memory as a child of the
       pointer.	It is logically	equivalent to:

	   talloc_set_name_const(ptr, talloc_asprintf(ptr, fmt,	...));

       Note that multiple calls	to talloc_set_name() will allocate more	memory
       without releasing the name. All of the memory is	released when the ptr
       is freed	using talloc_free().

   void	talloc_set_name_const(const void *ptr, const char *name);
       The function talloc_set_name_const() is just like talloc_set_name(),
       but it takes a string constant, and is much faster. It is extensively
       used by the "auto naming" macros, such as talloc_p().

       This function does not allocate any memory. It just copies the supplied
       pointer into the	internal representation	of the talloc ptr. This	means
       you must	not pass a name	pointer	to memory that will disappear before
       ptr is freed with talloc_free().

   void	*talloc_named(const void *ctx, size_t size, const char *fmt, ...);
       The talloc_named() function creates a named talloc pointer. It is
       equivalent to:

	   ptr = talloc_size(ctx, size);
	   talloc_set_name(ptr,	fmt, ....);

   void	*talloc_named_const(const void *ctx, size_t size, const	char *name);
       This is equivalent to:

	   ptr = talloc_size(ctx, size);
	   talloc_set_name_const(ptr, name);

   const char *talloc_get_name(const void *ptr);
       This returns the	current	name for the given talloc pointer, ptr.	See
       "talloc_set_name()" for details.

   void	*talloc_init(const char	*fmt, ...);
       This function creates a zero length named talloc	context	as a top level
       context.	It is equivalent to:

	   talloc_named(NULL, 0, fmt, ...);

   void	*talloc_new(void *ctx);
       This is a utility macro that creates a new memory context hanging off
       an existing context, automatically naming it "talloc_new: __location__"
       where __location__ is the source	line it	is called from.	It is
       particularly useful for creating	a new temporary	working	context.

   (type *)talloc_realloc(const	void *ctx, void	*ptr, type, count);
       The talloc_realloc() macro changes the size of a	talloc pointer.	It has
       the following equivalences:

	   talloc_realloc(ctx, NULL, type, 1) ==> talloc(ctx, type);
	   talloc_realloc(ctx, ptr, type, 0)  ==> talloc_free(ptr);

       The ctx argument	is only	used if	ptr is not NULL, otherwise it is
       ignored.

       talloc_realloc()	returns	the new	pointer, or NULL on failure. The call
       will fail either	due to a lack of memory, or because the	pointer	has
       more than one parent (see "talloc_reference()").

   void	*talloc_realloc_size(const void	*ctx, void *ptr, size_t	size);
       the talloc_realloc_size() function is useful when the type is not known
       so the type-safe	talloc_realloc() cannot	be used.

   TYPE	*talloc_steal(const void *new_ctx, const TYPE *ptr);
       The talloc_steal() function changes the parent context of a talloc
       pointer.	It is typically	used when the context that the pointer is
       currently a child of is going to	be freed and you wish to keep the
       memory for a longer time.

       The talloc_steal() function returns the pointer that you	pass it. It
       does not	have any failure modes.

       It is possible to produce loops in the parent/child relationship	if you
       are not careful with talloc_steal(). No guarantees are provided as to
       your sanity or the safety of your data if you do	this.

       Note that if you	try and	call talloc_steal() on a pointer that has more
       than one	parent then the	result is ambiguous. Talloc will choose	to
       remove the parent that is currently indicated by	talloc_parent()	and
       replace it with the chosen parent. You will also	get a message like
       this via	the talloc logging functions:

		  WARNING: talloc_steal	with references	at some_dir/source/foo.c:123
		     reference at some_dir/source/other.c:325
		     reference at some_dir/source/third.c:121

       To unambiguously	change the parent of a pointer please see the function
       "talloc_reparent()". See	the talloc_set_log_fn()	documentation for more
       information on talloc logging.

   TYPE	*talloc_reparent(const void *old_parent, const void *new_parent, const
       TYPE *ptr);
       The talloc_reparent() function changes the parent context of a talloc
       pointer.	It is typically	used when the context that the pointer is
       currently a child of is going to	be freed and you wish to keep the
       memory for a longer time.

       The talloc_reparent() function returns the pointer that you pass	it. It
       does not	have any failure modes.

       The difference between talloc_reparent()	and talloc_steal() is that
       talloc_reparent() can specify which parent you wish to change. This is
       useful when a pointer has multiple parents via references.

   TYPE	*talloc_move(const void	*new_ctx, TYPE **ptr);
       The talloc_move() function is a wrapper around talloc_steal() which
       zeros the source	pointer	after the move.	This avoids a potential	source
       of bugs where a programmer leaves a pointer in two structures, and uses
       the pointer from	the old	structure after	it has been moved to a new
       one.

   size_t talloc_total_size(const void *ptr);
       The talloc_total_size() function	returns	the total size in bytes	used
       by this pointer and all child pointers. Mostly useful for debugging.

       Passing NULL is allowed,	but it will only give a	meaningful result if
       talloc_enable_leak_report() or talloc_enable_leak_report_full() has
       been called.

   size_t talloc_total_blocks(const void *ptr);
       The talloc_total_blocks() function returns the total memory block count
       used by this pointer and	all child pointers. Mostly useful for
       debugging.

       Passing NULL is allowed,	but it will only give a	meaningful result if
       talloc_enable_leak_report() or talloc_enable_leak_report_full() has
       been called.

   void	talloc_report(const void *ptr, FILE *f);
       The talloc_report() function prints a summary report of all memory used
       by ptr. One line	of report is printed for each immediate	child of ptr,
       showing the total memory	and number of blocks used by that child.

       You can pass NULL for the pointer, in which case	a report is printed
       for the top level memory	context, but only if
       talloc_enable_leak_report() or talloc_enable_leak_report_full() has
       been called.

   void	talloc_report_full(const void *ptr, FILE *f);
       This provides a more detailed report than talloc_report(). It will
       recursively print the entire tree of memory referenced by the pointer.
       References in the tree are shown	by giving the name of the pointer that
       is referenced.

       You can pass NULL for the pointer, in which case	a report is printed
       for the top level memory	context, but only if
       talloc_enable_leak_report() or talloc_enable_leak_report_full() has
       been called.

       void talloc_report_depth_cb(const void *ptr, int	depth, int max_depth,
				   void	(*callback)(const void *ptr, int depth,	int max_depth, int is_ref, void	*priv),
				   void	*priv);

       This provides a more flexible reports than talloc_report(). It will
       recursively call	the callback for the entire tree of memory referenced
       by the pointer. References in the tree are passed with is_ref = 1 and
       the pointer that	is referenced.

       You can pass NULL for the pointer, in which case	a report is printed
       for the top level memory	context, but only if
       talloc_enable_leak_report() or talloc_enable_leak_report_full() has
       been called.

       The recursion is	stopped	when depth >= max_depth. max_depth = -1	means
       only stop at leaf nodes.

       void talloc_report_depth_file(const void	*ptr, int depth,
				     int max_depth, FILE *f);

       This provides a more flexible reports than talloc_report(). It will let
       you specify the depth and max_depth.

   void	talloc_enable_leak_report(void);
       This enables calling of talloc_report(NULL, stderr) when	the program
       exits. In Samba4	this is	enabled	by using the --leak-report command
       line option.

       For it to be useful, this function must be called before	any other
       talloc function as it establishes a "null context" that acts as the top
       of the tree. If you don't call this function first then passing NULL to
       talloc_report() or talloc_report_full() won't give you the full tree
       printout.

       Here is a typical talloc	report:

	   talloc report on 'null_context' (total 267 bytes in 15 blocks)
	   libcli/auth/spnego_parse.c:55  contains   31	bytes in   2 blocks
	   libcli/auth/spnego_parse.c:55  contains   31	bytes in   2 blocks
	   iconv(UTF8,CP850)		  contains   42	bytes in   2 blocks
	   libcli/auth/spnego_parse.c:55  contains   31	bytes in   2 blocks
	   iconv(CP850,UTF8)		  contains   42	bytes in   2 blocks
	   iconv(UTF8,UTF-16LE)		  contains   45	bytes in   2 blocks
	   iconv(UTF-16LE,UTF8)		  contains   45	bytes in   2 blocks

   void	talloc_enable_leak_report_full(void);
       This enables calling of talloc_report_full(NULL,	stderr)	when the
       program exits. In Samba4	this is	enabled	by using the
       --leak-report-full command line option.

       For it to be useful, this function must be called before	any other
       talloc function as it establishes a "null context" that acts as the top
       of the tree. If you don't call this function first then passing NULL to
       talloc_report() or talloc_report_full() won't give you the full tree
       printout.

       Here is a typical full report:

	   full	talloc report on 'root'	(total 18 bytes	in 8 blocks)
	   p1		    contains	 18 bytes in   7 blocks	(ref 0)
	       r1		contains     13	bytes in   2 blocks (ref 0)
		   reference to: p2
	       p2		contains      1	bytes in   1 blocks (ref 1)
	       x3		contains      1	bytes in   1 blocks (ref 0)
	       x2		contains      1	bytes in   1 blocks (ref 0)
	       x1		contains      1	bytes in   1 blocks (ref 0)

   (type *)talloc_zero(const void *ctx,	type);
       The talloc_zero() macro is equivalent to:

	   ptr = talloc(ctx, type);
	   if (ptr) memset(ptr,	0, sizeof(type));

   void	*talloc_zero_size(const	void *ctx, size_t size)
       The talloc_zero_size() function is useful when you don't	have a known
       type.

   void	*talloc_memdup(const void *ctx,	const void *p, size_t size);
       The talloc_memdup() function is equivalent to:

	   ptr = talloc_size(ctx, size);
	   if (ptr) memcpy(ptr,	p, size);

   char	*talloc_strdup(const void *ctx,	const char *p);
       The talloc_strdup() function is equivalent to:

	   ptr = talloc_size(ctx, strlen(p)+1);
	   if (ptr) memcpy(ptr,	p, strlen(p)+1);

       This function sets the name of the new pointer to the passed string.
       This is equivalent to:

	   talloc_set_name_const(ptr, ptr)

   char	*talloc_strndup(const void *t, const char *p, size_t n);
       The talloc_strndup() function is	the talloc equivalent of the C library
       function	strndup(3).

       This function sets the name of the new pointer to the passed string.
       This is equivalent to:

	   talloc_set_name_const(ptr, ptr)

   char	*talloc_vasprintf(const	void *t, const char *fmt, va_list ap);
       The talloc_vasprintf() function is the talloc equivalent	of the C
       library function	vasprintf(3).

       This function sets the name of the new pointer to the new string. This
       is equivalent to:

	   talloc_set_name_const(ptr, ptr)

   char	*talloc_asprintf(const void *t,	const char *fmt, ...);
       The talloc_asprintf() function is the talloc equivalent of the C
       library function	asprintf(3).

       This function sets the name of the new pointer to the passed string.
       This is equivalent to:

	   talloc_set_name_const(ptr, ptr)

   char	*talloc_asprintf_append(char *s, const char *fmt, ...);
       The talloc_asprintf_append() function appends the given formatted
       string to the given string.

       This function sets the name of the new pointer to the new string. This
       is equivalent to:

	   talloc_set_name_const(ptr, ptr)

   (type *)talloc_array(const void *ctx, type, unsigned	int count);
       The talloc_array() macro	is equivalent to:

	   (type *)talloc_size(ctx, sizeof(type) * count);

       except that it provides integer overflow	protection for the multiply,
       returning NULL if the multiply overflows.

   void	*talloc_array_size(const void *ctx, size_t size, unsigned int count);
       The talloc_array_size() function	is useful when the type	is not known.
       It operates in the same way as talloc_array(), but takes	a size instead
       of a type.

   (typeof(ptr)) talloc_array_ptrtype(const void *ctx, ptr, unsigned int
       count);
       The talloc_ptrtype() macro should be used when you have a pointer to an
       array and want to allocate memory of an array to	point at with this
       pointer.	When compiling with gcc	>= 3 it	is typesafe. Note this is a
       wrapper of talloc_array_size() and talloc_get_name() will return	the
       current location	in the source file. and	not the	type.

   void	*talloc_realloc_fn(const void *ctx, void *ptr, size_t size)
       This is a non-macro version of talloc_realloc(),	which is useful	as
       libraries sometimes want	a realloc function pointer. A realloc(3)
       implementation encapsulates the functionality of	malloc(3), free(3) and
       realloc(3) in one call, which is	why it is useful to be able to pass
       around a	single function	pointer.

   void	*talloc_autofree_context(void);
       This is a handy utility function	that returns a talloc context which
       will be automatically freed on program exit. This can be	used to	reduce
       the noise in memory leak	reports.

   void	*talloc_check_name(const void *ptr, const char *name);
       This function checks if a pointer has the specified name. If it does
       then the	pointer	is returned. It	it doesn't then	NULL is	returned.

   (type *)talloc_get_type(const void *ptr, type);
       This macro allows you to	do type	checking on talloc pointers. It	is
       particularly useful for void* private pointers. It is equivalent	to
       this:

	   (type *)talloc_check_name(ptr, #type)

   talloc_set_type(const void *ptr, type);
       This macro allows you to	force the name of a pointer to be a particular
       type. This can be used in conjunction with talloc_get_type() to do type
       checking	on void* pointers.

       It is equivalent	to this:

	   talloc_set_name_const(ptr, #type)

   talloc_set_log_fn(void (*log_fn)(const char *message));
       This function sets a logging function that talloc will use for warnings
       and errors. By default talloc will not print any	warnings or errors.

   talloc_set_log_stderr(void);
       This sets the talloc log	function to write log messages to stderr

PERFORMANCE
       All the additional features of talloc(3)	over malloc(3) do come at a
       price. We have a	simple performance test	in Samba4 that measures
       talloc()	versus malloc()	performance, and it seems that talloc()	is
       about 10% slower	than malloc() on my x86	Debian Linux box. For Samba,
       the great reduction in code complexity that we get by using talloc
       makes this worthwhile, especially as the	total overhead of
       talloc/malloc in	Samba is already quite small.

SEE ALSO
       malloc(3), strndup(3), vasprintf(3), asprintf(3),
       http://talloc.samba.org/

AUTHOR
       The original Samba software and related utilities were created by
       Andrew Tridgell.	Samba is now developed by the Samba Team as an Open
       Source project similar to the way the Linux kernel is developed.

COPYRIGHT/LICENSE
       Copyright (C) Andrew Tridgell 2004

       This program 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 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/.

Samba 4.0			  2015-04-10			     TALLOC(3)

NAME | SYNOPSIS | DESCRIPTION | TALLOC API | PERFORMANCE | SEE ALSO | AUTHOR | COPYRIGHT/LICENSE

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