talloc_tos in shadow_copy2_insert_string
clawsoon at yahoo.com
Tue Mar 27 11:03:17 MDT 2012
--- On Tue, 3/27/12, Volker Lendecke <Volker.Lendecke at SerNet.DE> wrote:
> From talloc_stackframe.h:
> * Implement a stack of talloc frames.
> * When a new talloc stackframe is allocated with
> * talloc_stackframe(), then
> * the TALLOC_CTX returned with talloc_tos() is reset to
> * that new
> * frame. Whenever that stack frame is TALLOC_FREE()'ed,
> * then the reverse
> * happens: The previous talloc_tos() is restored.
> * This API is designed to be robust in the sense that if
> * someone forgets to
> * TALLOC_FREE() a stackframe, then the next outer one
> * correctly cleans up and
> * resets the talloc_tos().
> The intended use is that talloc_tos() is used for anything
> within a function. Returning something on talloc_tos() is
> not the best style, because it means that this object will
> go away once the surrounding talloc_stackframe() goes. It
> will work okay if used in a controlled manner, but
> depending on local circumstances alternatives might be more
I read that code comment a few times but didn't fully understand it; thanks for the further explanation.
I've noticed this in my testing:
static void bar_alloc_string(char *barstring)
barstring = talloc_asprintf(talloc_tos(), "%s/%s", "foo", "bar");
static char *baz_alloc_string(void)
bazstring = talloc_asprintf(talloc_tos(), "%s/%s", "foo", "bar");
static int vfs_tallocfoobar_stat(vfs_handle_struct *handle,
struct smb_filename *smb_fname)
char *barstring = NULL;
DEBUG(0, ("bar string -> '%s'\n", barstring));
/* outputs "bar string -> '(null)'" */
/* Freed. */
DEBUG(0, ("baz string -> '%s'\n", baz_alloc_string()));
/* outputs "baz string -> 'foo/baz'" */
/* Not freed. */
I am right to guess based on this (before finding some proper documentation to read) that memory on a function's stack which is returned with "return" (rather than attached to a passed-in pointer) gets attached to the caller's stack, and that's why talloc isn't automatically freeing the baz result?
Thanks again for your help.
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