On Wed, Aug 26, 2015 at 03:26:08PM +0200, Patrik Jakobsson wrote:
> On Tue, Aug 25, 2015 at 11:12 PM, Mike Frysinger <vapier@xxxxxxxxxx> wrote:
> > 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@xxxxxxxxxxxxxxx>
> >> ---
> >> 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
>
> Yes, that's a good idea. My use case is pretty simple but usage can easliy grow.
>
> I'll resend this patch and take it out of the drm/i915 series.
>
> -Patrik
Here's my take on it (I assume it needs some discussion):
int
set_tcb_priv_data(struct tcb *tcp, void *priv_data)
{
/* A free callback is required before setting private data and private
* data must be set back to NULL before being set again.
*/
if (tcp->_free_priv_data == NULL ||
(tcp->_priv_data && priv_data != NULL))
return -1;
tcp->_priv_data = priv_data;
return 0;
}
void *
get_tcb_priv_data(struct tcb *tcp)
{
return tcp->_priv_data;
}
int
set_tcb_free_priv_data(struct tcb *tcp, void (*free_priv_data)(void *))
{
/* _free_priv_data must be set back to NULL before being set again. */
if (tcp->_free_priv_data && free_priv_data != NULL)
return -1;
tcp->_free_priv_data = free_priv_data;
return 0;
}
void
free_tcb_priv_data(struct tcb *tcp)
{
if (tcp->_priv_data) {
if (tcp->_free_priv_data) {
tcp->_free_priv_data(tcp->_priv_data);
tcp->_free_priv_data = NULL;
}
tcp->_priv_data = NULL;
}
}
Cheers
Patrik
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