[PATCH v4 2/5] drm: Add private data field to trace control block

[Mike Frysinger]

On 24 Aug 2015 14:42, Patrik Jakobsson wrote:
> We need to be able to store private data in the tcb across it's
> lifetime. To ensure proper destruction of the data a free_priv_data
> callback must be provided if an allocation is stored in priv_data. The
> callback is executed automatically when the life of the tcb ends.
> 
> * defs.h: Add extern declaration of free_tcb_priv_data.
>  (struct tcb): Add priv_data and free_priv_data.
> * strace.c (free_tcb_priv_data): New function
> (drop_tcb): Execute free_tcb_priv_data callback
> * syscall.c (trace_syscall_exiting): Execute free_tcb_priv_data callback
> 
> Signed-off-by: Patrik Jakobsson <patrik.jakobsson at linux.intel.com>
> ---
>  defs.h    |  6 ++++++
>  strace.c  | 14 ++++++++++++++
>  syscall.c |  1 +
>  3 files changed, 21 insertions(+)
> 
> diff --git a/defs.h b/defs.h
> index 9059026..bc3bd83 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -266,6 +266,10 @@ struct tcb {
>  	int u_error;		/* Error code */
>  	long scno;		/* System call number */
>  	long u_arg[MAX_ARGS];	/* System call arguments */
> +
> +	void *priv_data;	/* Private data for syscall decoding functions */
> +	void (*free_priv_data)(void *); /* Callback for freeing priv_data */

should we name these _priv_data and _free_priv_data and provides accessor
functions ?  i worry that code paths might stomp on each other by accident
and we don't end up noticing.

static void set_tcb_priv_data(struct tcb *tcp, void *data, void (*free_data)(void *))
{
	assert(tcp->_priv_data == NULL && tcp->_free_priv_data == NULL);
	...
}
-mike
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