linux-kernel - Re: [patch 2/5] signalfd v2

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Date:	Thu, 8 Mar 2007 11:33:35 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"David M. Lloyd" <dmlloyd@...rg.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 2/5] signalfd v2 - signalfd core ...

On Thu, 8 Mar 2007, Linus Torvalds wrote:

> 
> 
> On Thu, 8 Mar 2007, Davide Libenzi wrote:
> >
> > So, to cut it short, I can do the pseudo-siginfo read(2), but I don't 
> > like it too much (little, actually). The siginfo, as bad as it is, is a 
> > standard used in many POSIX APIs (hence even in kernel), and IMO if we 
> > want to send that back, a struct siginfo should be.
> > No?
> 
> I think it's perfectly fine if you make it "struct siginfo" (even though I 
> think it's a singularly ugly struct). It's just that then you'd have to 
> make your read() know whether it's a compat-read or not, which you really 
> can't.
> 
> Which is why you introduced a new system call, but that leads to all the 
> problems with the file descriptor no longer being *usable*.
> 
> Think scripts. It's easy to do reads in perl scripts, and parse the 
> output. In contrast, making perl use a new system call is quite 
> challenging.
> 
> And *that* is why "everything is a stream of bytes" is so important. You 
> don't know where the file descriptor has been, or who uses it. Special 
> system calls for special file descriptors are just *wrong*.
> 
> After all, that's why we'd have a signalfd() in the first place: exactly 
> so that you do *not* have to use special system calls, but can just pass 
> it on to any event waiting mechanism like select, poll, epoll. The same is 
> just *even*more*true* when it comes to reading the data!

"Cheeseburger it is!" ;)
I'll revert back to read(2) with pseudo-siginfo and O_NONBLOCK handling...



- Davide


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