On Wed, Jun 24, 2020 at 07:29:44PM +0100, Matthew Wilcox wrote: > On Wed, Jun 24, 2020 at 08:24:37PM +0200, Christoph Hellwig wrote: > > On Wed, Jun 24, 2020 at 11:20:26AM -0700, Linus Torvalds wrote: > > > On Wed, Jun 24, 2020 at 11:14 AM Christoph Hellwig <[email protected]> wrote: > > > > > > > > So we'd need new user copy functions for just those cases > > > > > > No. We'd open-code them. They'd look at "oh, I'm supposed to use a > > > kernel pointer" and just use those. > > > > > > IOW, basically IN THE CODE that cares (and the whole argument is that > > > this code is one or two special cases) you do > > > > > > /* This has not been converted to the new world order */ > > > if (get_fs() == KERNEL_DS) memcpy(..) else copy_from_user(); > > > > > > You're overdesigning things. You're making them more complex than they > > > need to be. > > > > I wish it was so simple. I really don't like overdesigns, trust me. > > > > But please take a look at setsockopt and all the different instances > > (count 90 .setsockopt wireups, and they then branch out into > > various subroutines as well). I really don't want to open code that > > there, but we could do helper specific to setsockopt. > > Can we do a setsockopt_iter() which replaces optval/optlen with an iov_iter?
We could. The only downside is int-sized sockopts are common, and used in the fast path of networking applications (e.g. cork,uncork) and this might introduce enough overhead to be noticable.
