From 4f5791ebd03eaec1c7da0865a383175b05102712 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 5 May 2024 19:47:29 +0200 Subject: Adding upstream version 2:4.17.12+dfsg. Signed-off-by: Daniel Baumann --- lib/talloc/doc/tutorial_stealing.dox | 55 ++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 lib/talloc/doc/tutorial_stealing.dox (limited to 'lib/talloc/doc/tutorial_stealing.dox') diff --git a/lib/talloc/doc/tutorial_stealing.dox b/lib/talloc/doc/tutorial_stealing.dox new file mode 100644 index 0000000..67eae1d --- /dev/null +++ b/lib/talloc/doc/tutorial_stealing.dox @@ -0,0 +1,55 @@ +/** +@page libtalloc_stealing Chapter 2: Stealing a context + +@section stealing Stealing a context + +Talloc has the ability to change the parent of a talloc context to another +one. This operation is commonly referred to as stealing and it is one of +the most important actions performed with talloc contexts. + +Stealing a context is necessary if we want the pointer to outlive the context it +is created on. This has many possible use cases, for instance stealing a result +of a database search to an in-memory cache context, changing the parent of a +field of a generic structure to a more specific one or vice-versa. The most +common scenario, at least in Samba, is to steal output data from a function-specific +context to the output context given as an argument of that function. + +@code +struct foo { + char *a1; + char *a2; + char *a3; +}; + +struct bar { + char *wurst; + struct foo *foo; +}; + +struct foo *foo = talloc_zero(ctx, struct foo); +foo->a1 = talloc_strdup(foo, "a1"); +foo->a2 = talloc_strdup(foo, "a2"); +foo->a3 = talloc_strdup(foo, "a3"); + +struct bar *bar = talloc_zero(NULL, struct bar); +/* change parent of foo from ctx to bar */ +bar->foo = talloc_steal(bar, foo); + +/* or do the same but assign foo = NULL */ +bar->foo = talloc_move(bar, &foo); +@endcode + +The talloc_move() function is similar to the talloc_steal() function but +additionally sets the source pointer to NULL. + +In general, the source pointer itself is not changed (it only replaces the +parent in the meta data). But the common usage is that the result is +assigned to another variable, thus further accessing the pointer from the +original variable should be avoided unless it is necessary. In this case +talloc_move() is the preferred way of stealing a context. Additionally sets the +source pointer to NULL, thus.protects the pointer from being accidentally freed +and accessed using the old variable after its parent has been changed. + +@image html stealing.png + +*/ -- cgit v1.2.3