Re: [PATCH] ptrace: add ability to retrieve signals without removing them from a queue

[Pavel Emelyanov <xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On 02/21/2013 02:37 AM, Oleg Nesterov wrote:
> On 02/19, Pavel Emelyanov wrote:
>>
>> On 02/19/2013 11:34 PM, Oleg Nesterov wrote:
>>> But, given that every PEEK does list_for_each() until it finds the
>>> necessary sequence number, I am wondering how this O(n**2) will work
>>> if you want to dump 126065 signals ;)
>>
>> Isn't it the great reason for making the addr point to a structure, that
>> would look like
>>
>> struct siginfo_peek_arg {
>> 	unsigned flags; /* all bits but 0th, that selects between private/shared
>> 			   queues, should be zero */
>> 	unsigned int off; /* from which siginfo to start */
>> 	unsigned int nr; /* how may siginfos to take */
>> };
> 
> I am fine either way, to me everything looks better than signalfd
> hacks.
> 
> But if you meant "avoid n^2", this won't help? You can't do
> copy_siginfo_to_user() under ->siglock, so you need to restart
> list_for_each() anyway.

Or allocate intermediate buffer putting the siginfo's there.

> Oleg.

Thanks,
Pavel