From: Greg KH <gregkh@linuxfoundation.org>
To: Nicolas Boichat <drinkcat@chromium.org>
Cc: Ian Lance Taylor <iant@golang.org>,
Dave Chinner <david@fromorbit.com>,
"Darrick J. Wong" <djwong@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Luis Lozano <llozano@chromium.org>,
linux-fsdevel@vger.kernel.org,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated
Date: Mon, 15 Feb 2021 09:30:28 +0100 [thread overview]
Message-ID: <YCoxJBlc0XrNjVPF@kroah.com> (raw)
In-Reply-To: <CANMq1KDv-brWeKOTt3aUUi_1SOXSpEFo5pS5A6mpRT8k-O88nA@mail.gmail.com>
On Mon, Feb 15, 2021 at 09:25:36AM +0800, Nicolas Boichat wrote:
> On Mon, Feb 15, 2021 at 9:12 AM Ian Lance Taylor <iant@golang.org> wrote:
> >
> > On Sun, Feb 14, 2021 at 4:38 PM Dave Chinner <david@fromorbit.com> wrote:
> > >
> > > On Fri, Feb 12, 2021 at 03:54:48PM -0800, Darrick J. Wong wrote:
> > > > On Sat, Feb 13, 2021 at 10:27:26AM +1100, Dave Chinner wrote:
> > > >
> > > > > If you can't tell from userspace that a file has data in it other
> > > > > than by calling read() on it, then you can't use cfr on it.
> > > >
> > > > I don't know how to do that, Dave. :)
> > >
> > > If stat returns a non-zero size, then userspace knows it has at
> > > least that much data in it, whether it be zeros or previously
> > > written data. cfr will copy that data. The special zero length
> > > regular pipe files fail this simple "how much data is there to copy
> > > in this file" check...
> >
> > This suggests that if the Go standard library sees that
> > copy_file_range reads zero bytes, we should assume that it failed, and
> > should use the fallback path as though copy_file_range returned
> > EOPNOTSUPP or EINVAL. This will cause an extra system call for an
> > empty file, but as long as copy_file_range does not return an error
> > for cases that it does not support we are going to need an extra
> > system call anyhow.
> >
> > Does that seem like a possible mitigation? That is, are there cases
> > where copy_file_range will fail to do a correct copy, and will return
> > success, and will not return zero?
>
> I'm a bit worried about the sysfs files that report a 4096 bytes file
> size, for 2 reasons:
> - I'm not sure if the content _can_ actually be longer (I couldn't
> find a counterexample)
There are quite a few, look for binary sysfs files that are pipes from
hardware/firmware resources to userspace. /sys/firmware/efi/efivars/
has a number of them if you want to play around with it.
thanks,
greg k-h
next prev parent reply other threads:[~2021-02-15 8:31 UTC|newest]
Thread overview: 136+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-12 4:43 [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Nicolas Boichat
2021-02-12 4:44 ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Nicolas Boichat
2021-02-12 7:46 ` Greg KH
2021-02-12 8:20 ` Nicolas Boichat
2021-02-12 8:37 ` Greg KH
2021-02-12 15:33 ` Ian Lance Taylor
2021-02-12 15:45 ` Greg KH
2021-02-12 15:59 ` Ian Lance Taylor
2021-02-12 16:28 ` Greg KH
2021-02-12 20:22 ` Ian Lance Taylor
2021-02-12 23:03 ` Dave Chinner
2021-02-12 23:07 ` Ian Lance Taylor
2021-02-12 23:27 ` Dave Chinner
2021-02-12 23:54 ` Darrick J. Wong
2021-02-15 0:38 ` Dave Chinner
2021-02-15 1:12 ` Ian Lance Taylor
2021-02-15 1:25 ` Nicolas Boichat
2021-02-15 5:56 ` Amir Goldstein
2021-02-15 8:30 ` Greg KH [this message]
2021-02-12 8:22 ` Amir Goldstein
2021-02-12 8:39 ` Greg KH
2021-02-12 12:05 ` Luis Henriques
2021-02-12 12:18 ` Greg KH
2021-02-12 12:41 ` Luis Henriques
2021-02-12 14:11 ` Greg KH
2021-02-12 15:01 ` Luis Henriques
2021-02-15 6:12 ` Amir Goldstein
2021-02-15 10:39 ` Luis Henriques
2021-02-15 12:22 ` Luis Henriques
2021-02-15 14:23 ` Amir Goldstein
2021-02-15 14:51 ` Luis Henriques
2021-02-15 15:43 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Luis Henriques
2021-02-15 16:02 ` Trond Myklebust
2021-02-16 0:25 ` Steve French
2021-02-15 16:34 ` Amir Goldstein
2021-02-15 16:53 ` Trond Myklebust
2021-02-15 17:24 ` Amir Goldstein
2021-02-15 18:57 ` Trond Myklebust
2021-02-15 19:43 ` Amir Goldstein
2021-02-16 11:17 ` Luis Henriques
2021-02-16 11:28 ` gregkh
2021-02-16 12:01 ` Luis Henriques
2021-02-16 12:08 ` Greg KH
2021-02-16 13:51 ` Amir Goldstein
2021-02-16 16:42 ` Luis Henriques
2021-02-16 17:44 ` Amir Goldstein
2021-02-16 18:55 ` Luis Henriques
2021-02-16 19:20 ` Amir Goldstein
2021-02-16 19:27 ` Anna Schumaker
2021-02-16 19:31 ` Steve French
2021-02-16 19:40 ` Amir Goldstein
2021-02-16 21:15 ` Steve French
2021-02-17 8:08 ` Amir Goldstein
2021-02-17 17:26 ` [PATCH v3] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-17 20:47 ` Amir Goldstein
2021-02-18 0:56 ` Nicolas Boichat
2021-02-18 5:32 ` Olga Kornievskaia
2021-02-18 6:47 ` Amir Goldstein
2021-02-18 16:28 ` Olga Kornievskaia
2021-02-18 7:43 ` Christoph Hellwig
2021-02-18 0:50 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Andreas Dilger
2021-02-18 7:34 ` gregkh
2021-02-16 18:54 ` Andreas Dilger
2021-02-17 4:45 ` Nicolas Boichat
2021-02-18 7:42 ` Christoph Hellwig
2021-02-18 9:10 ` Amir Goldstein
2021-02-18 10:29 ` Luis Henriques
2021-02-18 12:15 ` Luis Henriques
2021-02-18 12:49 ` Amir Goldstein
2021-02-18 14:36 ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Luis Henriques
2021-02-18 14:58 ` Amir Goldstein
2021-02-18 15:17 ` [PATCH v5] " Luis Henriques
2021-02-18 15:53 ` Amir Goldstein
2021-02-18 16:35 ` Luis Henriques
2021-02-18 17:18 ` [PATCH v6] " Luis Henriques
2021-02-19 21:18 ` Olga Kornievskaia
2021-02-19 21:52 ` Amir Goldstein
2021-02-21 19:58 ` [PATCH v7] " Luis Henriques
2021-02-22 3:00 ` Nicolas Boichat
2021-02-22 10:24 ` [PATCH v8] " Luis Henriques
2021-02-22 10:46 ` Amir Goldstein
2021-02-22 16:25 ` dai.ngo
2021-02-23 10:32 ` Luis Henriques
2021-02-23 15:28 ` Amir Goldstein
2021-02-23 15:29 ` dai.ngo
2021-02-23 16:02 ` dai.ngo
2021-02-23 16:47 ` Amir Goldstein
2021-02-23 16:57 ` dai.ngo
[not found] ` <e3eed18b-fc7e-e687-608b-7f662017329c@oracle.com>
2021-02-23 17:33 ` Amir Goldstein
2021-02-24 0:13 ` dai.ngo
2021-02-23 17:56 ` Luis Henriques
2021-02-23 17:13 ` Olga Kornievskaia
2021-02-24 1:00 ` Olga Kornievskaia
2021-02-24 10:23 ` Luis Henriques
2021-02-24 10:44 ` Nicolas Boichat
2021-04-09 5:23 ` Nicolas Boichat
2021-04-09 13:39 ` Luis Henriques
2021-04-09 13:50 ` Amir Goldstein
2021-04-23 4:40 ` Nicolas Boichat
2021-05-03 8:54 ` Luis Henriques
2021-05-10 4:59 ` Amir Goldstein
2021-05-10 9:10 ` Luis Henriques
2021-02-24 14:23 ` [PATCH] copy_file_range.2: Kernel v5.12 updates Luis Henriques
2021-02-24 16:10 ` Amir Goldstein
2021-02-25 10:21 ` Luis Henriques
2021-02-26 10:13 ` Alejandro Colomar (man-pages)
2021-02-26 10:34 ` Amir Goldstein
2021-02-26 11:15 ` Alejandro Colomar (man-pages)
2021-02-26 13:59 ` Jeff Layton
2021-02-26 21:26 ` Alejandro Colomar (man-pages)
2021-02-26 22:18 ` Alejandro Colomar (man-pages)
2021-02-27 5:41 ` Amir Goldstein
2021-02-27 12:20 ` Alejandro Colomar (man-pages)
2021-02-27 13:49 ` [RFC v2] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-02-27 16:00 ` Amir Goldstein
2021-02-27 23:08 ` [PATCH] copy_file_range.2: Kernel v5.12 updates Steve French
2021-02-28 7:35 ` Amir Goldstein
2021-02-28 22:25 ` Steve French
2021-03-01 6:18 ` Amir Goldstein
2021-03-01 14:41 ` [RFC v3] copy_file_range.2: Update cross-filesystem support for 5.12 Alejandro Colomar
2021-03-01 14:58 ` Amir Goldstein
2021-03-04 9:38 ` [RFC v4] " Alejandro Colomar
2021-03-04 17:13 ` Darrick J. Wong
2021-03-04 18:24 ` Alejandro Colomar (man-pages)
2021-03-04 23:50 ` Darrick J. Wong
2021-02-24 7:15 ` [PATCH v4] vfs: fix copy_file_range regression in cross-fs copies Amir Goldstein
2021-02-24 8:30 ` Petr Vorel
2021-02-18 20:41 ` [PATCH v2] vfs: prevent copy_file_range to copy across devices Steve French
2021-02-12 23:15 ` [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated Dave Chinner
2021-02-12 7:54 ` Amir Goldstein
2021-02-12 4:44 ` [PATCH 2/6] proc: Add FS_GENERATED_CONTENT to filesystem flags Nicolas Boichat
2021-02-12 4:44 ` [PATCH 6/6] vfs: Disallow copy_file_range on generated file systems Nicolas Boichat
2021-02-12 4:53 ` Darrick J. Wong
2021-02-12 4:59 ` Darrick J. Wong
2021-02-12 5:24 ` Nicolas Boichat
2021-02-14 23:09 ` [PATCH 0/6] Add generated flag to filesystem struct to block copy_file_range Al Viro
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