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From: Greg KH <>
To: Linus Torvalds <>,
	Christoph Hellwig <>
Cc: Al Viro <>,
	Linux Kernel Mailing List <>
Subject: problems with splice from /proc (was Linux 5.10-rc1)
Date: Tue, 27 Oct 2020 07:48:32 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, Oct 25, 2020 at 03:40:27PM -0700, Linus Torvalds wrote:
> The most interesting - to me - change here is Christoph's setf_fs()
> removal (it got merged through Al Viro, as you can see in my mergelog
> below).  It's not a _huge_ change, but it's interesting because the
> whole model of set_fs() to specify whether a userspace copy actually
> goes to user space or kernel space goes back to pretty much the
> original release of Linux, and while the name is entirely historic (it
> hasn't used the %fs segment register in a long time), the concept has
> remained. Until now.

I told Al this yesterday, but figured I would mention it here for others
to see.

Commit 36e2c7421f02 ("fs: don't allow splice read/write without explicit
ops") from this patch series, is breaking the bionic test suite that
does the following to verify that splice is working:

	int in = open("/proc/cpuinfo", O_RDONLY);
	ASSERT_NE(in, -1);

	TemporaryFile tf;
	ssize_t bytes_read = splice(in, nullptr, pipe_fds[1], nullptr, 8*1024, SPLICE_F_MORE | SPLICE_F_MOVE);
	ASSERT_NE(bytes_read, -1);

Before this change, all works well but now splice fails on /proc files
(and I'm guessing other virtual filesystems).

I'll ask the bionic developers if they can change their test to some
other file, but this is a regression and might show up in other "test
platforms" as well.  Using /proc for this is just so simple because
these files are "always there" and don't require any housekeeping for
test suites to worry about .


greg k-h

  parent reply	other threads:[~2020-10-27  6:49 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-25 22:40 Linux 5.10-rc1 Linus Torvalds
2020-10-25 23:43 ` linux-next: stats Stephen Rothwell
2020-10-27  6:48 ` Greg KH [this message]
2020-10-27  7:49   ` problems with splice from /proc (was Linux 5.10-rc1) Christoph Hellwig
2020-10-27  7:55     ` Greg KH
2020-10-27  8:07       ` Christoph Hellwig
2020-10-27  8:14         ` Greg KH
2020-10-27  8:14           ` Christoph Hellwig
2020-10-27  9:17           ` Greg KH
2020-10-27 16:32             ` Christoph Hellwig
2020-10-27 17:43               ` Greg KH
2020-10-28 16:00               ` Greg KH
2020-10-28 18:33                 ` Greg KH
2020-10-28 18:34                   ` Christoph Hellwig
2020-10-28 18:35                   ` [PATCH] proc "single files": switch to ->read_iter Greg Kroah-Hartman

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