samba-mirror/lib/talloc/talloc.3.xml

<?xml version="1.0"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<refentry>
  <refmeta>
    <refentrytitle>talloc</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>
  <refnamediv>
    <refname>talloc</refname>
<refpurpose>hierarchical reference counted memory pool system with destructors</refpurpose>
  </refnamediv>
  <refsynopsisdiv>
<synopsis>#include &lt;talloc.h&gt;</synopsis>
  </refsynopsisdiv>
  <refsect1><title>DESCRIPTION</title>
    <para>
      If you are used to talloc from Samba3 then please read this
      carefully, as talloc has changed a lot.
    </para>
    <para>
      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.
    </para>
    <para>
      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:
    </para>
    <programlisting>
    struct foo *X = talloc(mem_ctx, struct foo);
    X->name = talloc_strdup(X, "foo");
    </programlisting>
    <para>
      and the pointer <literal role="code">X-&gt;name</literal>
      would be a "child" of the talloc context <literal
      role="code">X</literal> which is itself a child of
      <literal role="code">mem_ctx</literal>.  So if you do
      <literal role="code">talloc_free(mem_ctx)</literal> then
      it is all destroyed, whereas if you do <literal
      role="code">talloc_free(X)</literal> then just <literal
      role="code">X</literal> and <literal
      role="code">X-&gt;name</literal> are destroyed, and if
      you do <literal
      role="code">talloc_free(X-&gt;name)</literal> then just
      the name element of <literal role="code">X</literal> is
      destroyed.
    </para>
    <para>
      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().
    </para>
    <para>
      If you find this confusing, then I suggest you run the <literal
      role="code">testsuite</literal> program to watch talloc
      in action.  You may also like to add your own tests to <literal
      role="code">testsuite.c</literal> to clarify how some
      particular situation is handled.
    </para>
  </refsect1>
  <refsect1><title>TALLOC API</title>
    <para>
      The following is a complete guide to the talloc API. Read it all at
      least twice.
    </para>
    <refsect2><title>(type *)talloc(const void *ctx, type);</title>
        <para>
	  The talloc() macro is the core of the talloc library.  It takes a
	  memory <emphasis role="italic">ctx</emphasis> and a <emphasis
	  role="italic">type</emphasis>, and returns a pointer to a new
	  area of memory of the given <emphasis
	  role="italic">type</emphasis>.
        </para>
        <para>
	  The returned pointer is itself a talloc context, so you can use
	  it as the <emphasis role="italic">ctx</emphasis> argument to more
	  calls to talloc() if you wish.
        </para>
        <para>
	  The returned pointer is a "child" of the supplied context.  This
	  means that if you talloc_free() the <emphasis
	  role="italic">ctx</emphasis> then the new child disappears as
	  well.  Alternatively you can free just the child.
        </para>
        <para>
	  The <emphasis role="italic">ctx</emphasis> argument to talloc()
	  can be NULL, in which case a new top level context is created.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_size(const void *ctx, size_t size);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>(typeof(ptr)) talloc_ptrtype(const void *ctx, ptr);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>int talloc_free(void *ptr);</title>
        <para>
	  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().
        </para>
        <para>
	  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 <emphasis
	  role="italic">ptr</emphasis> had a destructor attached to it and
	  the destructor returned -1.  See <link
	  linkend="talloc_set_destructor"><quote>talloc_set_destructor()</quote></link>
	  for details on destructors.
        </para>
        <para>
	  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 <link
	  linkend="talloc_reference"><quote>talloc_reference()</quote></link>
	  for details on establishing additional parents.
        </para>
        <para>
	  For more control on which parent is removed, see <link
	  linkend="talloc_unlink"><quote>talloc_unlink()</quote></link>.
        </para>
        <para>
	  talloc_free() operates recursively on its children.
        </para>
	<para>
	  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().
	</para>
	<para>
	  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:
	</para>
	<para>
	  <screen format="linespecific">
	    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
	  </screen>
	</para>
	<para>
	  Please see the documentation for talloc_set_log_fn() and
	  talloc_set_log_stderr() for more information on talloc logging
	  functions.
	</para>
    </refsect2>
    <refsect2 id="talloc_reference"><title>void *talloc_reference(const void *ctx, const void *ptr);</title>
        <para>
	  The talloc_reference() function makes <emphasis
	  role="italic">ctx</emphasis> an additional parent of <emphasis
	  role="italic">ptr</emphasis>.
        </para>
        <para>
	  The return value of talloc_reference() is always the original
	  pointer <emphasis role="italic">ptr</emphasis>, 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).
        </para>
        <para>
	  If <emphasis role="italic">ptr</emphasis> is NULL, then the
	  function is a no-op, and simply returns NULL.
        </para>
        <para>
	  After creating a reference you can free it in one of the
	  following ways:
        </para>
      <para>
        <itemizedlist>
          <listitem>
            <para>
	      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.
            </para>
          </listitem>
          <listitem>
            <para>
	      you can talloc_free() the pointer itself.  That will destroy
	      the most recently established parent to the pointer and leave
	      the pointer as a child of its current parent.
            </para>
          </listitem>
        </itemizedlist>
      </para>
      <para>
	For more control on which parent to remove, see <link
	linkend="talloc_unlink"><quote>talloc_unlink()</quote></link>.
      </para>
    </refsect2>
    <refsect2 id="talloc_unlink"><title>int talloc_unlink(const void *ctx, const void *ptr);</title>
        <para>
	  The talloc_unlink() function removes a specific parent from
	  <emphasis role="italic">ptr</emphasis>. The <emphasis
	  role="italic">ctx</emphasis> passed must either be a context used
	  in talloc_reference() with this pointer, or must be a direct
	  parent of ptr.
        </para>
        <para>
	  Note that if the parent has already been removed using
	  talloc_free() then this function will fail and will return -1. 
	  Likewise, if <emphasis role="italic">ptr</emphasis> is NULL, then
	  the function will make no modifications and return -1.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2 id="talloc_set_destructor"><title>void talloc_set_destructor(const void *ptr, int (*destructor)(void *));</title>
        <para>
	  The function talloc_set_destructor() sets the <emphasis
	  role="italic">destructor</emphasis> for the pointer <emphasis
	  role="italic">ptr</emphasis>.  A <emphasis
	  role="italic">destructor</emphasis> is a function that is called
	  when the memory used by a pointer is about to be released.  The
	  destructor receives <emphasis role="italic">ptr</emphasis> as an
	  argument, and should return 0 for success and -1 for failure.
        </para>
        <para>
	  The <emphasis role="italic">destructor</emphasis> 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.
        </para>
        <para>
	  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.
        </para>
        <para>
	  To remove a destructor call talloc_set_destructor() with NULL for
	  the destructor.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>int talloc_increase_ref_count(const void *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  The talloc_increase_ref_count(<emphasis
	  role="italic">ptr</emphasis>) function is exactly equivalent to:
        </para>
        <programlisting>talloc_reference(NULL, ptr);</programlisting>
        <para>
	  You can use either syntax, depending on which you think is
	  clearer in your code.
        </para>
        <para>
	  It returns 0 on success and -1 on failure.
        </para>
    </refsect2>
    <refsect2><title>size_t talloc_reference_count(const void *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  Return the number of references to the pointer.
        </para>
    </refsect2>
    <refsect2 id="talloc_set_name"><title>void talloc_set_name(const void *ptr, const char *fmt, ...);</title>
        <para>
	  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.
        </para>
        <para>
	  The main use for names on pointer is for "talloc reports".  See
	  <link
	  linkend="talloc_report"><quote>talloc_report_depth_cb()</quote></link>,
	  <link
	  linkend="talloc_report"><quote>talloc_report_depth_file()</quote></link>,
	  <link
	  linkend="talloc_report"><quote>talloc_report()</quote></link>
	  <link
	  linkend="talloc_report"><quote>talloc_report()</quote></link>
	  and <link
	  linkend="talloc_report_full"><quote>talloc_report_full()</quote></link>
	  for details.	Also see <link
	  linkend="talloc_enable_leak_report"><quote>talloc_enable_leak_report()</quote></link>
	  and <link
	  linkend="talloc_enable_leak_report_full"><quote>talloc_enable_leak_report_full()</quote></link>.
        </para>
        <para>
	  The talloc_set_name() function allocates memory as a child of the
	  pointer.  It is logically equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, talloc_asprintf(ptr, fmt, ...));</programlisting>
        <para>
	  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().
        </para>
    </refsect2>
    <refsect2><title>void talloc_set_name_const(const void *<emphasis role="italic">ptr</emphasis>, const char *<emphasis role="italic">name</emphasis>);</title>
        <para>
	  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().
        </para>
        <para>
	  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 <emphasis
	  role="italic">name</emphasis> pointer to memory that will
	  disappear before <emphasis role="italic">ptr</emphasis> is freed
	  with talloc_free().
        </para>
    </refsect2>
    <refsect2><title>void *talloc_named(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, ...);</title>
        <para>
	  The talloc_named() function creates a named talloc pointer.  It
	  is equivalent to:
        </para>
        <programlisting>ptr = talloc_size(ctx, size);
talloc_set_name(ptr, fmt, ....);</programlisting>
    </refsect2>
    <refsect2><title>void *talloc_named_const(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>, const char *<emphasis role="italic">name</emphasis>);</title>
        <para>
	  This is equivalent to:
        </para>
        <programlisting>ptr = talloc_size(ctx, size);
talloc_set_name_const(ptr, name);</programlisting>
    </refsect2>
    <refsect2><title>const char *talloc_get_name(const void *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  This returns the current name for the given talloc pointer,
	  <emphasis role="italic">ptr</emphasis>. See <link
	  linkend="talloc_set_name"><quote>talloc_set_name()</quote></link>
	  for details.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_init(const char *<emphasis role="italic">fmt</emphasis>, ...);</title>
        <para>
	  This function creates a zero length named talloc context as a top
	  level context.  It is equivalent to:
        </para>
        <programlisting>talloc_named(NULL, 0, fmt, ...);</programlisting>
    </refsect2>
    <refsect2><title>void *talloc_new(void *<emphasis role="italic">ctx</emphasis>);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>(<emphasis role="italic">type</emphasis> *)talloc_realloc(const void *<emphasis role="italic">ctx</emphasis>, void *<emphasis role="italic">ptr</emphasis>, <emphasis role="italic">type</emphasis>, <emphasis role="italic">count</emphasis>);</title>
        <para>
	  The talloc_realloc() macro changes the size of a talloc pointer. 
	  It has the following equivalences:
        </para>
        <programlisting>talloc_realloc(ctx, NULL, type, 1) ==> talloc(ctx, type);
talloc_realloc(ctx, ptr, type, 0)  ==> talloc_free(ptr);</programlisting>
        <para>
	  The <emphasis role="italic">ctx</emphasis> argument is only used
	  if <emphasis role="italic">ptr</emphasis> is not NULL, otherwise
	  it is ignored.
        </para>
        <para>
	  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 <link
	  linkend="talloc_reference"><quote>talloc_reference()</quote></link>).
        </para>
    </refsect2>
    <refsect2><title>void *talloc_realloc_size(const void *ctx, void *ptr, size_t size);</title>
        <para>
	  the talloc_realloc_size() function is useful when the type is not
	  known so the type-safe talloc_realloc() cannot be used.
        </para>
    </refsect2>
    <refsect2><title>TYPE *talloc_steal(const void *<emphasis role="italic">new_ctx</emphasis>, const TYPE *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  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.
        </para>
        <para>
	  The talloc_steal() function returns the pointer that you pass it.
	   It does not have any failure modes.
        </para>
        <para>
	  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.
        </para>
        <para>
	  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:
        </para>
        <para>
	  <screen format="linespecific">
	  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
	  </screen>
        </para>
        <para>
	  To unambiguously change the parent of a pointer please see
	  the
	  function <link linkend="talloc_reference"><quote>talloc_reparent()</quote></link>. See
	  the talloc_set_log_fn() documentation for more information
	  on talloc logging.  
	</para>
    </refsect2>
    <refsect2><title>TYPE *talloc_reparent(const void *<emphasis role="italic">old_parent</emphasis>, const void *<emphasis role="italic">new_parent</emphasis>, const TYPE *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  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.
        </para>
        <para>
	  The talloc_reparent() function returns the pointer that you pass it. It
	  does not have any failure modes.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>TYPE *talloc_move(const void *<emphasis role="italic">new_ctx</emphasis>, TYPE **<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>size_t talloc_total_size(const void *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  The talloc_total_size() function returns the total size in bytes
	  used by this pointer and all child pointers.	Mostly useful for
	  debugging.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>size_t talloc_total_blocks(const void *<emphasis role="italic">ptr</emphasis>);</title>
        <para>
	  The talloc_total_blocks() function returns the total memory block
	  count used by this pointer and all child pointers.  Mostly useful
	  for debugging.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2 id="talloc_report"><title>void talloc_report(const void *ptr, FILE *f);</title>
        <para>
	  The talloc_report() function prints a summary report of all
	  memory used by <emphasis role="italic">ptr</emphasis>.  One line
	  of report is printed for each immediate child of ptr, showing the
	  total memory and number of blocks used by that child.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2 id="talloc_report_full"><title>void talloc_report_full(const void *<emphasis role="italic">ptr</emphasis>, FILE *<emphasis role="italic">f</emphasis>);</title>
        <para>
	  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.
        </para>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2 id="talloc_report_depth_cb">
     <funcsynopsis><funcprototype>
      <funcdef>void <function>talloc_report_depth_cb</function></funcdef>
      <paramdef><parameter>const void *ptr</parameter></paramdef>
      <paramdef><parameter>int depth</parameter></paramdef>
      <paramdef><parameter>int max_depth</parameter></paramdef>
      <paramdef><parameter>void (*callback)(const void *ptr, int depth, int max_depth, int is_ref, void *priv)</parameter></paramdef>
      <paramdef><parameter>void *priv</parameter></paramdef>
     </funcprototype></funcsynopsis>
        <para>
	  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
	  <emphasis role="italic">is_ref = 1</emphasis> and the pointer that is referenced.
        </para>
        <para>
	  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.
        </para>
        <para>
	  The recursion is stopped when depth >= max_depth.
	  max_depth = -1 means only stop at leaf nodes.
        </para>
    </refsect2>
    <refsect2 id="talloc_report_depth_file">
     <funcsynopsis><funcprototype>
      <funcdef>void <function>talloc_report_depth_file</function></funcdef>
      <paramdef><parameter>const void *ptr</parameter></paramdef>
      <paramdef><parameter>int depth</parameter></paramdef>
      <paramdef><parameter>int max_depth</parameter></paramdef>
      <paramdef><parameter>FILE *f</parameter></paramdef>
     </funcprototype></funcsynopsis>
        <para>
	  This provides a more flexible reports than talloc_report(). It
	  will let you specify the depth and max_depth.
        </para>
    </refsect2>
    <refsect2 id="talloc_enable_leak_report"><title>void talloc_enable_leak_report(void);</title>
        <para>
	  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.
        </para>
        <para>
	  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.
        </para>
        <para>
	  Here is a typical talloc report:
        </para>
        <screen format="linespecific">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
      </screen>
    </refsect2>
    <refsect2 id="talloc_enable_leak_report_full"><title>void talloc_enable_leak_report_full(void);</title>
        <para>
	  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.
        </para>
        <para>
	  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.
        </para>
        <para>
	  Here is a typical full report:
        </para>
        <screen format="linespecific">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)
      </screen>
    </refsect2>
    <refsect2><title>(<emphasis role="italic">type</emphasis> *)talloc_zero(const void *<emphasis role="italic">ctx</emphasis>, <emphasis role="italic">type</emphasis>);</title>
        <para>
	  The talloc_zero() macro is equivalent to:
        </para>
        <programlisting>ptr = talloc(ctx, type);
if (ptr) memset(ptr, 0, sizeof(type));</programlisting>
    </refsect2>
    <refsect2><title>void *talloc_zero_size(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>)</title>
        <para>
	  The talloc_zero_size() function is useful when you don't have a
	  known type.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_memdup(const void *<emphasis role="italic">ctx</emphasis>, const void *<emphasis role="italic">p</emphasis>, size_t size);</title>
        <para>
	  The talloc_memdup() function is equivalent to:
        </para>
        <programlisting>ptr = talloc_size(ctx, size);
if (ptr) memcpy(ptr, p, size);</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_strdup(const void *<emphasis role="italic">ctx</emphasis>, const char *<emphasis role="italic">p</emphasis>);</title>
        <para>
	  The talloc_strdup() function is equivalent to:
        </para>
        <programlisting>ptr = talloc_size(ctx, strlen(p)+1);
if (ptr) memcpy(ptr, p, strlen(p)+1);</programlisting>
        <para>
	  This function sets the name of the new pointer to the passed
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_strndup(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">p</emphasis>, size_t <emphasis role="italic">n</emphasis>);</title>
        <para>
	  The talloc_strndup() function is the talloc equivalent of the C
	  library function strndup(3).
        </para>
        <para>
	  This function sets the name of the new pointer to the passed
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_append_string(const void *<emphasis role="italic">t</emphasis>, char *<emphasis role="italic">orig</emphasis>, const char *<emphasis role="italic">append</emphasis>);</title>
        <para>
	  The talloc_append_string() function appends the given formatted
	  string to the given string.
        </para>
        <para>
	  This function sets the name of the new pointer to the new
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_vasprintf(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, va_list <emphasis role="italic">ap</emphasis>);</title>
        <para>
	  The talloc_vasprintf() function is the talloc equivalent of the C
	  library function vasprintf(3).
        </para>
        <para>
	  This function sets the name of the new pointer to the new
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_asprintf(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, ...);</title>
        <para>
	  The talloc_asprintf() function is the talloc equivalent of the C
	  library function asprintf(3).
        </para>
        <para>
	  This function sets the name of the new pointer to the passed
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>char *talloc_asprintf_append(char *s, const char *fmt, ...);</title>
        <para>
	  The talloc_asprintf_append() function appends the given formatted
	  string to the given string.
        </para>
        <para>
	  This function sets the name of the new pointer to the new
	  string. This is equivalent to:
        </para>
        <programlisting>talloc_set_name_const(ptr, ptr)</programlisting>
    </refsect2>
    <refsect2><title>(type *)talloc_array(const void *ctx, type, unsigned int count);</title>
        <para>
	  The talloc_array() macro is equivalent to:
        </para>
        <programlisting>(type *)talloc_size(ctx, sizeof(type) * count);</programlisting>
        <para>
	  except that it provides integer overflow protection for the
	  multiply, returning NULL if the multiply overflows.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_array_size(const void *ctx, size_t size, unsigned int count);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>(typeof(ptr)) talloc_array_ptrtype(const void *ctx, ptr, unsigned int count);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_realloc_fn(const void *ctx, void *ptr, size_t size)</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_autofree_context(void);</title>
        <para>
	  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.
        </para>
    </refsect2>
    <refsect2><title>void *talloc_check_name(const void *ptr, const char *name);</title>
        <para>
	  This function checks if a pointer has the specified <emphasis
	  role="italic">name</emphasis>.  If it does then the pointer is
	  returned.  It it doesn't then NULL is returned.
        </para>
    </refsect2>
    <refsect2><title>(type *)talloc_get_type(const void *ptr, type);</title>
        <para>
	  This macro allows you to do type checking on talloc pointers.  It
	  is particularly useful for void* private pointers.  It is
	  equivalent to this:
        </para>
        <programlisting>(type *)talloc_check_name(ptr, #type)</programlisting>
    </refsect2>
    <refsect2><title>talloc_set_type(const void *ptr, type);</title>
        <para>
	  This macro allows you to force the name of a pointer to be a
	  particular <emphasis>type</emphasis>.  This can be
	  used in conjunction with talloc_get_type() to do type checking on
	  void* pointers.
        </para>
        <para>
	  It is equivalent to this:
        </para>
        <programlisting>talloc_set_name_const(ptr, #type)</programlisting>
    </refsect2>
    <refsect2><title>talloc_set_log_fn(void (*log_fn)(const char *message));</title>
        <para>
	  This function sets a logging function that talloc will use for
	  warnings and errors. By default talloc will not print any warnings or
	  errors.
	</para>
    </refsect2>
    <refsect2><title>talloc_set_log_stderr(void);</title>
        <para>
	  This sets the talloc log function to write log messages to stderr
	</para>
    </refsect2>
  </refsect1>
  <refsect1><title>PERFORMANCE</title>
    <para>
      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.
    </para>
  </refsect1>
  <refsect1><title>SEE ALSO</title>
    <para>
      malloc(3), strndup(3), vasprintf(3), asprintf(3), 
      <ulink url="http://talloc.samba.org/"/>
    </para>
  </refsect1>
  <refsect1><title>COPYRIGHT/LICENSE</title>
    <para>
      Copyright (C) Andrew Tridgell 2004
    </para>
    <para>
      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.
    </para>
    <para>
      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.
    </para>
    <para>
      You should have received a copy of the GNU General Public License
      along with this program; if not, see http://www.gnu.org/licenses/.
    </para>
  </refsect1>
</refentry>