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SubjectRe: Splicing to/from a tty
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On Mon, 2021-01-18 at 09:53 +0100, Christoph Hellwig wrote:
> On Sat, Jan 16, 2021 at 05:46:33PM +0100, Johannes Berg wrote:
> > > 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().
>
> Yes, pipes do not support ->splice_write currenly.

Well, it clearly used to work :-)

> I think just wiring
> up iter_file_splice_write would work. Al?

Seems to work for the simple test case that I had, at least:

diff --git a/fs/pipe.c b/fs/pipe.c
index c5989cfd564d..39c96845a72f 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1206,6 +1206,7 @@ const struct file_operations pipefifo_fops = {
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
.fasync = pipe_fasync,
+ .splice_write = iter_file_splice_write,
};

/*
johannes

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