linux-kernel - Re: [PATCH 1/4] inet: Add skb_copy_datagram

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Message-ID: <20141105022251.GA19136@gondor.apana.org.au>
Date:	Wed, 5 Nov 2014 10:22:51 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 1/4] inet: Add skb_copy_datagram_iter

On Tue, Nov 04, 2014 at 03:13:55PM +0000, Al Viro wrote:
> 
> Think of it that way: every sendmsg/recvmsg path leading to memcpy_fromiovec
> and its friends (including the open-coded ones) would need to be changed
> at some point.  Assuming we do not end up passing struct iov_iter * as
> an extra argument through a fairly large part of net/* (and that would
> be prohibitively hard and messy, not to mention the effects on the stack
> footprint, etc.), the most obvious strategy is to have that thing passed
> where msg_iov/msg_iovlen are - in struct msghdr.  *IF* we go that way,
> it makes a whole lot of sense to start with a bunch of cleanups that
> will make sense on their own (most of callers of skb_copy_datagram_iovec
> do look like skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied); might
> as well give it an inlined helper) and will reduce the amount of places
> where ->msg_iov is used.  With such cleanups standing on their own and
> being splittable from the rest of the queue.  And leaving us with fewer
> places in code that deal with ->msg_iov and need to be dealt with.

I think your solution is great.  However, I don't see how my four
patches impede in anyway the work that you're doing.  I presume
your first patch will make skb_copy_datagram_msg just a wrapper
around skb_copy_datagram_iovec.

Since I'm not removing skb_copy_datagram_iovec (it can't be removed
until all users are gone) you can still do that and when you're
ready to switch over to iov_iter you can just move the wrapper over
to skb_copy_datagram_iter.  No?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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