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

[Dmitry Safonov]

2017-03-27 18:13 GMT+03:00 Dmitry Safonov <0x7f454c46 at gmail.com>:
> 2017-03-27 17:25 GMT+03:00 Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>:
>>
>>
>> 27.03.2017 16:07, Dmitry Safonov пишет:
>>>
>>> Yes, but fini_sigreturn() at this moment is called only for parasite-based
>>> infection. While the patch exports API for non-parasite case of infection.
>>> So, as I've asked before, can we complement it with usage of the formed
>>> sigframe in the case of non-parasite infection?
>>> It may be just a helper that has inside compel_syscall() with
>>> rt_sigreturn.
>>> I mean, if anyone is going to use API for forming sigframe, he will
>>> have to write such helper. Maybe it's better to provide one for integrity?
>>>
>>
>> It's not that simple.
>> User has to provide address *within* process address space, where sigframe
>> must be placed, *to* sigframe creation routine.
>> IOW, one need:
>> 1) Some service mapping within process (doesn't exist in non-parasite case
>> of infection), which he can use to store sigframe
>> 2) Some way to call sigreturn from *within* the process (doesn't exist in
>> non-parasite case of infection)
>> 3) Calling to "rt_sigreturn" needs this sigframe address.
>>
>> Thus, from my POW, libcompel can to provide this helper "as is".
>> Or this facility has to be significantly improved by hiding all this remote
>> mapping creation, sigrame construction and rt_sigreturn call to some kind of
>> helpers like below:
>>
>> int compel_put_some_straw(struct parasite_ctl *ctl);
>>
>> and paired (static, inlined, whatever else to prevent linking with
>> libcompel):
>>
>> int compel_fall_from_the tree(void);
>>
>
> Well, I would vote for something like:
>
> compel_remote_mmap(struct parasite_ctl *ctl, unsigned long addr)
> /* actually renamed compel_unmap() */

Oh, actually, not renamed, but reworked :-/
Also, need to add `unsigned long size' to parameters list.

> compel_remote_unmap(struct parasite_ctl *ctl, unsigned long addr)
> compel_sigframe_prepare(struct rt_sigframe *raddr,
>    user_regs_struct_t *regs, k_rtsigset_t* sig)
> compel_sigframe_sigreturn(struct rt_sigframe *raddr)
>
> Maybe the naming could be improved.
> This way we would have complete API for preparing sigframes for any
> register set, blocked signals mask and for sigreturning to constructed
> frames. All without parasite's help.
>
> Otherwise the original patch exports API for preparing sigframe only
> at the point where an application was stopped and leaves reader's
> exercise what to do with this sigframe afterward.
>
> What do you think, is it convenient API for your project?
> I don't insist, but that looks logical to me avoiding inchoate APIs.
>
> --
>              Dmitry



-- 
             Dmitry