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Date: Thu, 21 May 2020 08:01:33 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Christoph Hellwig' <hch@....de>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org> CC: Eric Dumazet <edumazet@...gle.com>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, "Vlad Yasevich" <vyasevich@...il.com>, Neil Horman <nhorman@...driver.com>, "Marcelo Ricardo Leitner" <marcelo.leitner@...il.com>, Jon Maloy <jmaloy@...hat.com>, Ying Xue <ying.xue@...driver.com>, "drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>, "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>, "linux-afs@...ts.infradead.org" <linux-afs@...ts.infradead.org>, "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>, "cluster-devel@...hat.com" <cluster-devel@...hat.com>, "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>, "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>, "rds-devel@....oracle.com" <rds-devel@....oracle.com>, "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org> Subject: RE: remove kernel_setsockopt and kernel_getsockopt v2 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)
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