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

From: Pavel Emelyanov
Date: Thu Feb 21 2013 - 05:31:07 EST

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.

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