On 8/13/06, Dinesh Ahuja <mdlinux7@xxxxxxxxxxx> wrote:
Hi Manish,
It is just a macro that expands to a for loop. It is
deffined in
sched.h
#define for_each_process(p) \
for (p = &init_task ; (p = next_task(p)) !=
&init_task ; )
Right this is a macro. On further investigation, I
found that init_task access init_task_union.task
{defined in include/asm-i386/processor.h} and
next_task is again a macro defined as
#define next_task(p) list_entry((p)->tasks.next,
struct task_struct, tasks)
list_entry is again a macro defined in
{include/linux/list.h} as
#define list_entry(ptr, type, member) \
((type *)((char *)(ptr)-(unsigned
long)(&((type *)0)->member)))
In this case, macro uses a init_task_union which is
exported by kernel and that should be sufficient for
module to iterate over list. But if macro is using an
kernel symbol i.e function or a global variable, then
these symbols should be exported otherwise use of
macro will give unresolved symbols. Please verfiy my
understanding.
correct.
I am trying to use read lock before iterating a task
list.
read_lock(&tasklist_lock);
for_each_process(p) {
printk ("<1> Iterating Task
List" );
}
read_unlock(&tasklist_lock);
But getting following error:
unresolved symbol __read_lock_failed
The tasklist_lock is a rw spinlock. It is again a macro defined in
<linux/spinlock.h>
regards
Manish Regmi
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