On Wed, Jan 17, 2018 at 11:26:08AM -0800, Linus Torvalds wrote: > But there are about ~100 set_fs() calls in generic code, and some of > those really are pretty fundamental. Doing things like "kernel_read()" > without set_fs() is basically impossible. Not if we move to iov_iter or iov_iter-like behavior for all reads and writes. There is an issue with how vectored writes are handles in plain read/write vs read_iter/write_iter inherited from readv/writev, but that's nothing a flag, or a second set of methods with the same signature. But there are more annoying things, most notable in-kernel ioctls calls. We have quite a few of them, and while many are just utterly stupid and can be replaced with direct function calls or new methods (I've done quite a few conversions of those) some might be left. Something like iov_iter might be the answer again. Then we have things like probe_kernel_read/probe_kernel_write which abuse the exception handling in get/put user. But with a little arch helper we don't strictly need get_fs/set_fs for that.
