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Date: Thu, 12 Jan 2017 22:58:46 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Alan J. Wylie" <alan@wylie.me.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Thorsten Leemhuis <regressions@leemhuis.info>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn
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On Thu, Jan 12, 2017 at 10:46:06PM +0000, Alan J. Wylie wrote:
> at 14:26 on Thu 12-Jan-2017 Linus Torvalds (torvalds@linux-foundation.org) wrote:

> 13761 copy_file_range(5, NULL, 1, NULL, 9223372036854775807, 0) = -1 EXDEV (Invalid cross-device link)
> 13761 sendfile(1, 5, NULL, 9223372036854775807) = -1 EINVAL (Invalid argument)
> 13761 splice(5, NULL, 1, NULL, 9223372036854775807, 0) = -1 EAGAIN (Resource temporarily unavailable)

*bleep*

splice from /dev/ptmx to stdout, whatever the latter had been.  IOW,
we are dealing with do_splice() -> do_splice_to() -> default_file_splice_read()
for pseudo-tty as source...