linux-kernel - Re: [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface.

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Date:	Fri, 18 Apr 2008 21:38:50 +0200
From:	"Michael Kerrisk" <mtk.manpages@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Rusty Russell" <rusty@...tcorp.com.au>, netdev@...r.kernel.org,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	"Michael Kerrisk" <mtk.manpages@...il.com>
Subject: Re: [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface.

On 4/18/08, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Sat, 19 Apr 2008 00:32:39 +1000 Rusty Russell <rusty@...tcorp.com.au> wrote:
>
>  > > Isn't this kinda-sorta like what a relayfs file does?  The oprofile
>  > > buffers?  etc?  Nothing in common at all, no hope?
>  >
>  > An excellent question, but I thought the modern kernel etiquette was to only
>  > comment on whitespace and formatting, and call it "review"? :)
>  >
>  > Yes, kinda-sorta in that it's a ring buffer.  No, in that it's bidir and
>  > consumption can be out-of-order (kind of important for I/O buffers).
>  >
>  > But the reason I'm not proposing it as a syscall is that I'm not convinced
>  > it's the One True Solution which everyone should be using.  Time will tell:
>  > it's clearly not tied to tun and it's been generically useful for virtual
>  > I/O, but history has not been kind to new userspace interfaces.
>
>
> This is may be our third high-bandwidth user/kernel interface to transport
>  bulk data ("hbukittbd") which was implemented because its predecessors
>  weren't quite right.  In a year or two's time someone else will need a
>  hbukittbd and will find that the existing three aren't quite right and will
>  give us another one.  One day we need to stop doing this ;)
>
>  It could be that this person will look at Rusty's hbukittbd and find that
>  it _could_ be tweaked to do what he wants, but it's already shipping and
>  it's part of the kernel API and hence can't be made to do what he wants.
>
>  So I think it would be good to plonk the proposed interface on the table
>  and have a poke at it.  Is it compat-safe?  Is it extensible in a
>  backward-compatible fashion?  Are there future-safe changes we should make
>  to it?  Can Michael Kerrisk understand, review and document it?  etc.

Well, it helps if he's CCed....

I'm happy to work *with someone* on the documentation (pointless to do
it on my own -- how do I know what Rusty's *intended* behavior for the
interface is), and review, and testing.
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