(what is probably the first in a plethora of silly questions as i
dig into the ugly details of various kernel features. you've been
warned.)
clawing my way through the kernel code for kthreads and i notice the
following. in kernel/kthread.c, we have:
===
struct kthread {
int should_stop;
void *data;
struct completion exited;
};
#define to_kthread(tsk) \
container_of((tsk)->vfork_done, struct kthread, exited)
===
in other words, the kthread to associated "task_struct" mapping is
based on the fact that this member field in task_struct:
struct completion *vfork_done; /* for vfork() */
will point at the "exited" completion object in the corresponding
"struct kthread".
is the above construct only true for kthreads, in the sense of,
unless you've specifically created a kthread, the vfork_done pointer
in task_struct is to a simple completion. but if the task is a
kthread, the vfork_done pointer is *still* to a completion, but it's a
completion that's encapsulated in a larger structure that's meant to
be manipulated by kthread routines, obviously.
as a test, i did this:
===
$ grep -r "container_of.*vfork_done" *
kernel/kthread.c: container_of((tsk)->vfork_done, struct kthread, exited)
$
===
so it appears that that vfork_done field is only ever "container_of"ed
with respect to kthreads and nowhere else.
thoughts?
rday
--
========================================================================
Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
LinkedIn: http://ca.linkedin.com/in/rpjday
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