On Tue, Oct 27, 2020 at 09:51:34AM +0000, David Howells wrote: > David Howells <dhowells@xxxxxxxxxx> wrote: > > > > default_file_splice_write is the last piece of generic code that uses > > > set_fs to make the uaccess routines operate on kernel pointers. It > > > implements a "fallback loop" for splicing from files that do not actually > > > provide a proper splice_read method. The usual file systems and other > > > high bandwith instances all provide a ->splice_read, so this just removes > > > support for various device drivers and procfs/debugfs files. If splice > > > support for any of those turns out to be important it can be added back > > > by switching them to the iter ops and using generic_file_splice_read. > > > > Hmmm... this causes the copy_file_range() syscall to fail with EINVAL in some > > places where before it used to work. > > > > For my part, it causes the generic/112 xfstest to fail with afs, but there may > > be other places. > > > > Is this a regression we need to fix in the VFS core? Or is it something we > > need to fix in xfstests and assume userspace will fallback to doing it itself? > > That said, for afs at least, the fix seems to be just this: And that is the correct fix, I was about to send it to you. We can't have a "generic" splice using ->read/->write without set_fs, in addition to the iter_file_splice_write based version being a lot more efficient than what you had before.
