[CRIU] [PATCH] compel: compel_emergency_sigframe() helper introduced

[Stanislav Kinsburskiy]

24.03.2017 11:14, Dmitry Safonov пишет:
> 2017-03-24 12:32 GMT+03:00 Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>:
>>
>> 24.03.2017 00:13, Andrei Vagin пишет:
>>
>>> On Fri, Mar 17, 2017 at 01:17:58PM +0300, Stanislav Kinsburskiy wrote:
>>>> This helper constructs sigframe, which can be used to resume process from
>>>> the
>>>> point where it was stopped.
>>>> Result has to be copied to the process manually and then used with
>>>> rt_sigreturn.
>>>>
>>>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
> [...]
>>>> --- a/compel/src/lib/infect.c
>>>> +++ b/compel/src/lib/infect.c
>>>> @@ -1162,6 +1162,20 @@ static int make_sigframe_plain(void *from, struct
>>>> rt_sigframe *f, struct rt_sigf
>>>>          return 0;
>>>>    }
>>>>    +int compel_emergency_sigframe(struct parasite_ctl *ctl, struct
>>>> rt_sigframe *f,
>>>> +                             struct rt_sigframe *rtf)
>>>> +{
>>>> +       pid_t pid = ctl->rpid;
>>>> +       struct thread_ctx *thread = &ctl->orig;
>>>> +       struct plain_regs_struct regs;
>>>> +
>>>> +       if (get_task_regs(pid, &thread->regs, save_regs_plain, &regs)) {
>>>> +               pr_err("Can't obtain regs for thread %d\n", pid);
>>>> +               return -1;
>>>> +       }
>>>> +       return make_sigframe_plain(&regs, f, rtf, &thread->sigmask);
>>> make_sigframe_plain is called from parasite_start_daemon(), why it
>>> doesn't work for you. Could you describe your usecase for these changes?
>>>
>> Because I don't have parasite plugin, on which parasite_start_daemon relies.
>> But it makes sense to use this new helper in parasite_start_daemon to make
>> sure it's tested.
> Maybe it worth not providing additional interfaces, but splitting the existing.
> If we can make non-parasite version of compel_infect() and reuse its code
> in parasite's one, so it'll suit criu's needs and needs of projects
> without parasite.
> Does it make sense?

Definitely.

> Also, this looks incomplete without curing part. How do you use
> prepared sigframe
> afterward? Calling rt_sigreturn() with the help of compel_syscall() or
> somehow alike?

Yes. Somehow alike.

> I guess, there should be also a patch to complement API.
> And (by @avagin's rules) - adding new API/features means adding tests for it,
> looks like it wouldn't take much time to write a test for this.

If this peace of code will be used by CRIU itself, then it looks like 
sufficient testing. No?