Re: dereferencing pointer to incomplete type ‘struct workqueue_struct’

[Arkady <arkady dot miasnikov at gmail dot com>]

The simplest way to resolve the problem is top copy the struct to the
inline C code

http://lxr.free-electrons.com/source/kernel/workqueue.c#L239

On Wed, Apr 26, 2017 at 6:20 PM, John Busch <jbusch175@gmail.com> wrote:
> Hello,
>
> I’m new to SystemTap, and trying to print information about kernel
> work queues.  I’ve used the example code in section 4.3 [1] of the
> tutorial as my starting point, and I’m working on an up-to-date Fedora
> 25 system.
>
> The example code in the tutorial works just fine.  However, when I
> essentially swap out variable and struct names to modify the example
> to walk through workqueue_structs (instead of task_structs), I get a
> “dereferencing pointer to incomplete type ‘struct workqueue_struct’”
> compilation error on the line containing list_for_each_safe.  Code
> sample below.
>
> workqueue_struct is defined in workqueue.h [2] and workqueue.c [4],
> and I’m trying to access the global variable system_wq [3, 5].  How
> would I gain access to these objects in systemtap?  I must be doing
> something wrong, but can't figure out what it is.
>
> Thanks!
>
> [1] https://sourceware.org/systemtap/tutorial/Tapsets.html
> [2] http://lxr.free-electrons.com/source/include/linux/workqueue.h#L16
> [3] http://lxr.free-electrons.com/source/include/linux/workqueue.h#L365
> [4] http://lxr.free-electrons.com/source/kernel/workqueue.c#L239
> [5] http://lxr.free-electrons.com/source/kernel/workqueue.c#L338
>
> %{
> #include <linux/workqueue.h>
> #include <linux/list.h>
> %}
>
> function read_wq_list:long ()
> %{
>    int ret = 0;
>    struct workqueue_struct *wq;
>    struct list_head *p, *n;
>
>    list_for_each_safe(p, n, system_wq->list) {
>        wq = list_entry(p, struct workqueue_struct, list);
>        _stp_printf("workqueue struct %s\n", wq->name);
>    }
>
>    STAP_RETURN(ret);
> %}
>
> probe begin
> {
> printf("reading list of workqueues\n")
> read_wq_list()
> exit()
> }