Thank you for your reply!
My words is a little confused:)
to simplify it, we assume fork1() is invoked by PT. In your words,"The kernel
thread stack is not copied
or shared between PT and CT" , but forklwp() invokes lwp_forkregs(lwp, clwp)
which to copy struct regs in kernel stack frame from PT to CT.
It means that CT will be dispatched to execute lwp_rtt_initial() in kernel
mode,which invoke IRET instruction to translate from kernel mode to userland.
because CT's kernel stack frame is copied from PT, it will execute the code
after fork() in PT.
*USER CODE AS FOLLOWS:*
////////////////////////////////
int ret = fork();
if (ret > 0) {
// in parent process
} else if (ret == 0) {
// in child process
}
////////////////////////////////
Yesterday I think that CT has no user thread struct named ulwpt_t, how it is to
control userland exuction flow?
Now It seems that the as struct is copied from PP to CP.PP and CP share the
same process address space this time.When CT to execute the text code,because
of copy on write(COW),the page frames involving ulwp_t struct will copied for
CP.Now CT has its own ulwp_t struct, it conforms to that a process's thread has
an ulwp_t struct, a klwp_t struct and a kthread_t struct.
Oh,Is That right?
> Date: Mon, 28 Sep 2009 09:24:35 -0700
> From: jonathan.adams at sun.com
> To: mydino_vi at hotmail.com
> CC: on-discuss at opensolaris.org
> Subject: Re: [on-discuss] question about cfort
>
> On Mon, Sep 28, 2009 at 09:09:42PM +0800, ?? ? wrote:
> >
> > For example,
> >
> > the some thread maked by PT in parent process marked by PP
> > invoked syscall fork(), cfork() is invoked in the kernel
> > state which create child process marked by CP, CP's proc
> > struct(as,p_exec,p_user,klwp_t/kthread pairs) is duplicated by PP's
> > proc.
>
> To re-write:
>
> Some thread (PT) in a process (PP) invoked the "fork" syscall, which
> causes the kernel function cfork() to be called. This creates a child
> process (CP), whose state is a duplicate of PP's.
>
> > Besides the kernel stack of CP's kthread is equal to the kernel
> > statck of PT,so CP's current thread is dispatched by cpu to execute
> > the code after fork() in PT thread code.
> >
> > Question:CP has no any user thread(ulwp_t), why not duplicate ulwp_t?
> >
> > Is PT's ulwp_t shared by PP and CP? if so, it is not conform
> > ulwp_t:klwp_t:kthread_t=1:1:1?!
>
> I'm not sure exactly what you're asking here. Assuming we're talking
> about fork1() (which only creates one thread in CP), cfork() will
> create a single thread (CT) in the child, using the "forklwp()"
> call, which creates threads and associated LWPs, and duplicates the
> *userland* thread state from PT. The kernel thread stack is not copied
> or shared between PT and CT; the CT starts out with an empty stack in
> lwp_rtt_initial(), an assembly routine which sets up the stack, does some
> initial dtrace probes, and returns to userland.
>
> Does that answer your question?
>
> Cheers,
> - jonathan
>
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