source: trunk/server/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_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 Lesser 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>