On Sat, 2021-01-16 at 20:35 +1300, Oliver Giles wrote: > Commit 36e2c7421f02 (fs: don't allow splice read/write without > explicit ops) broke my userspace application which talks to an SSL VPN > by splice()ing between "openssl s_client" and "pppd". The latter > operates over a pty, and since that commit there is no fallback for > splice()ing between a pipe and a pty, or any tty for that matter. > > The above commit mentions switching them to the iter ops and using > generic_file_splice_read. IIUC, this would require implementing iter > ops also on the line disciplines, which sounds pretty disruptive. > > For my case, I attempted to instead implement splice_write and > splice_read in tty_fops; I managed to get splice_write working calling > ld->ops->write, but splice_read is not so simple because the > tty_ldisc_ops read method expects a userspace buffer. So I cannot see > how to implement this without either (a) using set_fs, or (b) > implementing iter ops on all line disciplines. > > Is splice()ing between a tty and a pipe worth supporting at all? Not a > big deal for my use case at least, but it used to work.
Is it even strictly related to the tty? I was just now looking into why my cgit/fcgi/nginx setup no longer works, and the reason is getting -EINVAL from sendfile() when the input is a file and the output is a pipe(). So I wrote a simple test program (below) and that errors out on kernel 5.10.4, while it works fine on the 5.9.16 I currently have. Haven't tried reverting anything yet, but now that I haev a test program it should be simple to even bisect. johannes #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <sys/sendfile.h> #include <stdio.h> #include <assert.h> int main(int argc, char **argv) { int in = open(argv[0], O_RDONLY); int p[2], out; off_t off = 0; int err; assert(in >= 0); assert(pipe(p) >= 0); out = p[1]; err = sendfile(out, in, &off, 1024); if (err < 0) perror("sendfile"); assert(err == 1024); return 0; }