linux-kernel - Re: [patch 7/8] fdmap v2

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Date:	Thu, 7 Jun 2007 19:25:03 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Matt Mackall <mpm@...enic.com>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Thu, 7 Jun 2007, Matt Mackall wrote:
> 
> First, how does this work in-kernel? Does it set a flag in the thread
> struct that magically gets used in the actual syscall? Or do we pass
> flags down to the sys_foo() function in some manner?

Set a flag in the thread-struct.

In fact, that's how "access()" already works.

And yes, syslets would need to have their own thread-structs and/or 
save/restore the thing.

> Second, I think we're likely to run out of flag bits really quickly as
> this is a good dumping spot for patching up our many slightly
> brain-damaged APIs (be they POSIX or Linux-specific).

Well, I do suspect that we'd need to basically make the flags be 
per-system call. With "common features" (ie a system call that doesn't 
return a file descriptor would re-use the bit for "nonlinear-fd" for 
something else, while a system call that doesn't do path lookup would use 
all the LOOKUP_xyzzy bits for something else).

I agree that if we kept flags _totally_ separate, we'd run out of them 
really quickly. But I don't think we want to ever be in the situation 
where _one_ set of system calls would need that many flags. If we get 
there, we'd really be much better off with a new system call!

> Third, can I do sys_indirect(sys_indirect(foo, args), flags1), flags2)?

I'd say no.

> Fourth, can we do sys_indirect(foo, args, flags | ASYNC) and get most
> of the way to merging this with the syslet proposal?

I think that may well be a really good idea.

		Linus
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