From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH] ptrace: add ability to retrieve signals without removing them from a queue Date: Wed, 20 Feb 2013 23:37:03 +0100 Message-ID: <20130220223703.GB16194@redhat.com> References: <1360768595-31943-1-git-send-email-avagin@openvz.org> <5123BC20.9040405@parallels.com> <20130219193424.GA9606@redhat.com> <5123D6D6.7010904@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <5123D6D6.7010904-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pavel Emelyanov Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Andrey Vagin , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, criu-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Roland McGrath , Andrew Morton , "Paul E. McKenney" , David Howells , Dave Jones , Linus Torvalds List-Id: linux-api@vger.kernel.org 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. Oleg.