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From: Greg KH <gregkh@linuxfoundation.org>
To: Luis Henriques <lhenriques@suse.de>
Cc: Jeff Layton <jlayton@kernel.org>,
	Amir Goldstein <amir73il@gmail.com>,
	Nicolas Boichat <drinkcat@chromium.org>,
	"Darrick J . Wong" <djwong@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Ian Lance Taylor <iant@google.com>,
	Luis Lozano <llozano@chromium.org>,
	Dave Chinner <david@fromorbit.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated
Date: Fri, 12 Feb 2021 15:11:14 +0100	[thread overview]
Message-ID: <YCaMgtpCzPrLjw9c@kroah.com> (raw)
In-Reply-To: <87sg61ihkj.fsf@suse.de>

On Fri, Feb 12, 2021 at 12:41:48PM +0000, Luis Henriques wrote:
> Greg KH <gregkh@linuxfoundation.org> writes:
> 
> > On Fri, Feb 12, 2021 at 12:05:14PM +0000, Luis Henriques wrote:
> >> Greg KH <gregkh@linuxfoundation.org> writes:
> >> 
> >> > On Fri, Feb 12, 2021 at 10:22:16AM +0200, Amir Goldstein wrote:
> >> >> On Fri, Feb 12, 2021 at 9:49 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >> >> >
> >> >> > On Fri, Feb 12, 2021 at 12:44:00PM +0800, Nicolas Boichat wrote:
> >> >> > > Filesystems such as procfs and sysfs generate their content at
> >> >> > > runtime. This implies the file sizes do not usually match the
> >> >> > > amount of data that can be read from the file, and that seeking
> >> >> > > may not work as intended.
> >> >> > >
> >> >> > > This will be useful to disallow copy_file_range with input files
> >> >> > > from such filesystems.
> >> >> > >
> >> >> > > Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> >> >> > > ---
> >> >> > > I first thought of adding a new field to struct file_operations,
> >> >> > > but that doesn't quite scale as every single file creation
> >> >> > > operation would need to be modified.
> >> >> >
> >> >> > Even so, you missed a load of filesystems in the kernel with this patch
> >> >> > series, what makes the ones you did mark here different from the
> >> >> > "internal" filesystems that you did not?
> >> >> >
> >> >> > This feels wrong, why is userspace suddenly breaking?  What changed in
> >> >> > the kernel that caused this?  Procfs has been around for a _very_ long
> >> >> > time :)
> >> >> 
> >> >> That would be because of (v5.3):
> >> >> 
> >> >> 5dae222a5ff0 vfs: allow copy_file_range to copy across devices
> >> >> 
> >> >> The intention of this change (series) was to allow server side copy
> >> >> for nfs and cifs via copy_file_range().
> >> >> This is mostly work by Dave Chinner that I picked up following requests
> >> >> from the NFS folks.
> >> >> 
> >> >> But the above change also includes this generic change:
> >> >> 
> >> >> -       /* this could be relaxed once a method supports cross-fs copies */
> >> >> -       if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> >> >> -               return -EXDEV;
> >> >> -
> >> >> 
> >> >> The change of behavior was documented in the commit message.
> >> >> It was also documented in:
> >> >> 
> >> >> 88e75e2c5 copy_file_range.2: Kernel v5.3 updates
> >> >> 
> >> >> I think our rationale for the generic change was:
> >> >> "Why not? What could go wrong? (TM)"
> >> >> I am not sure if any workload really gained something from this
> >> >> kernel cross-fs CFR.
> >> >
> >> > Why not put that check back?
> >> >
> >> >> In retrospect, I think it would have been safer to allow cross-fs CFR
> >> >> only to the filesystems that implement ->{copy,remap}_file_range()...
> >> >
> >> > Why not make this change?  That seems easier and should fix this for
> >> > everyone, right?
> >> >
> >> >> Our option now are:
> >> >> - Restore the cross-fs restriction into generic_copy_file_range()
> >> >
> >> > Yes.
> >> >
> >> 
> >> Restoring this restriction will actually change the current cephfs CFR
> >> behaviour.  Since that commit we have allowed doing remote copies between
> >> different filesystems within the same ceph cluster.  See commit
> >> 6fd4e6348352 ("ceph: allow object copies across different filesystems in
> >> the same cluster").
> >> 
> >> Although I'm not aware of any current users for this scenario, the
> >> performance impact can actually be huge as it's the difference between
> >> asking the OSDs for copying a file and doing a full read+write on the
> >> client side.
> >
> > Regression in performance is ok if it fixes a regression for things that
> > used to work just fine in the past :)
> >
> > First rule, make it work.
> 
> Sure, I just wanted to point out that *maybe* there are other options than
> simply reverting that commit :-)
> 
> Something like the patch below (completely untested!) should revert to the
> old behaviour in filesystems that don't implement the CFR syscall.
> 
> Cheers,
> -- 
> Luis
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 75f764b43418..bf5dccc43cc9 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1406,8 +1406,11 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
>  						       file_out, pos_out,
>  						       len, flags);
>  
> -	return generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
> -				       flags);
> +	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> +		return -EXDEV;
> +	else
> +		generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
> +					flags);
>  }
>  
>  /*

That would make much more sense to me.

  reply	other threads:[~2021-02-12 14:12 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
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 [this message]
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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