linux-kernel - Re: Fix signalfd interaction with thread-private signals

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Message-Id: <1182578708.24740.95.camel@localhost.localdomain>
Date:	Sat, 23 Jun 2007 16:05:08 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Fix signalfd interaction with thread-private signals

On Fri, 2007-06-22 at 17:12 -0700, Davide Libenzi wrote:
> Wasn't it you that bitched (just a few days ago) because multiple
> threads 
> could not use the same signalfd and they (by your initial thought) had
> to 
> create one per thread?

He said multiple process and you say multiple threads...

If signalfd isn't attached to any context, it would then be useable by
all threads in a process, delivering them their private signals and the
process shared signals. Makes sense to me.

By removing that context thing, you lose the ability to listen to some
other -process- signals, which is probably a bad idea in the first place
anyway... if you're going to do that, use ptrace (yuck) :-)

Now, you -might- have valid uses for that later ability, but if not, it
then makes some sense to only "attach" when an actual read or poll is
done and only for the duration of that read/poll and only for that
reader/poller (not the whole signalfd instance).

I think that's what Nicholas means... and it may even simplify the code.

Ben.

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