From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: RE: remove kernel_setsockopt and kernel_getsockopt v2 Date: Thu, 21 May 2020 08:01:33 +0000 Message-ID: <138a17dfff244c089b95f129e4ea2f66@AcuMS.aculab.com> References: <20200520195509.2215098-1-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <20200520195509.2215098-1-hch@lst.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: 'Christoph Hellwig' , "David S. Miller" , Jakub Kicinski Cc: Eric Dumazet , Alexey Kuznetsov , Hideaki YOSHIFUJI , Vlad Yasevich , Neil Horman , Marcelo Ricardo Leitner , Jon Maloy , Ying Xue , "drbd-dev@lists.linbit.com" , "linux-kernel@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-nvme@lists.infradead.org" , "target-devel@vger.kernel.org" , "linux-afs@lists.infradead.org" , "linux-cifs@vger.kernel.org" , cluster-devel@redhat.co List-Id: ceph-devel.vger.kernel.org From: Christoph Hellwig > Sent: 20 May 2020 20:55 > > this series removes the kernel_setsockopt and kernel_getsockopt > functions, and instead switches their users to small functions that > implement setting (or in one case getting) a sockopt directly using > a normal kernel function call with type safety and all the other > benefits of not having a function call. > > In some cases these functions seem pretty heavy handed as they do > a lock_sock even for just setting a single variable, but this mirrors > the real setsockopt implementation unlike a few drivers that just set > set the fields directly. How much does this increase the kernel code by? You are also replicating a lot of code making it more difficult to maintain. I don't think the performance of an socket option code really matters - it is usually done once when a socket is initialised and the other costs of establishing a connection will dominate. Pulling the user copies outside the [gs]etsocksopt switch statement not only reduces the code size (source and object) and trivially allows kernel_[sg]sockopt() to me added to the list of socket calls. It probably isn't possible to pull the usercopies right out into the syscall wrapper because of some broken requests. I worried about whether getsockopt() should read the entire user buffer first. SCTP needs the some of it often (including a sockaddr_storage in one case), TCP needs it once. However the cost of reading a few words is small, and a big buffer probably needs setting to avoid leaking kernel memory if the structure has holes or fields that don't get set. Reading from userspace solves both issues. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)