From: Al Viro Subject: Re: [RFC] situation with csum_and_copy_... API Date: Fri, 21 Nov 2014 19:39:11 +0000 Message-ID: <20141121193911.GU7996@ZenIV.linux.org.uk> References: <20141119.161744.1661940121298888832.davem@davemloft.net> <20141119213006.GE7996@ZenIV.linux.org.uk> <20141119.165340.2162829993279387495.davem@davemloft.net> <20141120214753.GR7996@ZenIV.linux.org.uk> <1416520542.8629.46.camel@edumazet-glaptop2.roam.corp.google.com> <20141120222506.GS7996@ZenIV.linux.org.uk> <1416524035.8629.54.camel@edumazet-glaptop2.roam.corp.google.com> <20141121084956.GT7996@ZenIV.linux.org.uk> <063D6719AE5E284EB5DD2968C1650D6D1C9F6930@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , David Miller , "torvalds@linux-foundation.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "target-devel@vger.kernel.org" , "Nicholas A. Bellinger" , Christoph Hellwig To: David Laight Return-path: Content-Disposition: inline In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1C9F6930@AcuExch.aculab.com> Sender: target-devel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Nov 21, 2014 at 05:42:55PM +0000, David Laight wrote: > Callers of kernel_send/recvmsg() could easily be using a wrapper > function that creates the 'msghdr'. > When the want to send the remaining part of a buffer the old iterator > will no longer be available - just the original iov and the required offset. Er... So why not copy a struct iov_iter to/from msg->msg_iter, then? It's not as it had been particulary large - 5 words isn't much... I'm not at all sure that _anything_ has valid reasons for draining iovecs. Maintaining a struct iov_iter and modifying it is easy and actually faster... Right now the main examples outside of net/* are due to unfortunate limitations of ->sendmsg() - until now it had no way to be told that desired data starts at offset. With ->msg_iter it obviously becomes possible...