On Fri, May 07, 2021 at 07:05:51PM +0100, Colin Ian King wrote: > Hi, > > While doing some micro benchmarking with stress-ng I discovered that > since linux 5.9 the splicing from /dev/zero to a pipe now fails with > -EINVAL. > > I bisected this down to the following commit: > > 36e2c7421f02a22f71c9283e55fdb672a9eb58e7 is the first bad commit > commit 36e2c7421f02a22f71c9283e55fdb672a9eb58e7 > Author: Christoph Hellwig <hch@xxxxxx> > Date: Thu Sep 3 16:22:34 2020 +0200 > > fs: don't allow splice read/write without explicit ops > > I'm not sure if this has been reported before, or if it's intentional > behavior or not. As it stands, it's a regression in the stress-ng splice > test case. The general loss of generic splice read/write is known. Here's some early conversations I was involved in: https://lore.kernel.org/lkml/20200818200725.GA1081@xxxxxx/ https://lore.kernel.org/lkml/202009181443.C2179FB@keescook/ https://lore.kernel.org/lkml/20201005204517.2652730-1-keescook@xxxxxxxxxxxx/ And it's been getting re-implemented in individual places: $ git log --oneline --no-merges --grep 36e2c742 42984af09afc jffs2: Hook up splice_write callback a35d8f016e0b nilfs2: make splice write available again f8ad8187c3b5 fs/pipe: allow sendfile() to pipe again f2d6c2708bd8 kernfs: wire up ->splice_read and ->splice_write 9bb48c82aced tty: implement write_iter dd78b0c483e3 tty: implement read_iter 14e3e989f6a5 proc mountinfo: make splice available again c1048828c3db orangefs: add splice file operations 960f4f8a4e60 fs: 9p: add generic splice_write file operation cf03f316ad20 fs: 9p: add generic splice_read file operations 06a17bbe1d47 afs: Fix copy_file_range() So the question is likely, "do we want this for /dev/zero?" -- Kees Cook
