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From: Amir Goldstein <amir73il@gmail.com>
To: "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>
Cc: Luis Henriques <lhenriques@suse.de>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Jeff Layton <jlayton@kernel.org>,
	Steve French <sfrench@samba.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Dave Chinner <dchinner@redhat.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Nicolas Boichat <drinkcat@chromium.org>,
	Ian Lance Taylor <iant@google.com>,
	Luis Lozano <llozano@chromium.org>,
	Andreas Dilger <adilger@dilger.ca>,
	Olga Kornievskaia <aglo@umich.edu>,
	Christoph Hellwig <hch@infradead.org>,
	ceph-devel <ceph-devel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	CIFS <linux-cifs@vger.kernel.org>,
	samba-technical <samba-technical@lists.samba.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	linux-man <linux-man@vger.kernel.org>
Subject: Re: [PATCH] copy_file_range.2: Kernel v5.12 updates
Date: Sat, 27 Feb 2021 07:41:18 +0200	[thread overview]
Message-ID: <CAOQ4uxgFCBNwRD7e1srwaVrZMGfOE_JXENL4Q2En52srdj2AYA@mail.gmail.com> (raw)
In-Reply-To: <6b896b29-6fc1-0586-ef31-f2f3298b56b0@gmail.com>

On Sat, Feb 27, 2021 at 12:19 AM Alejandro Colomar (man-pages)
<alx.manpages@gmail.com> wrote:
>
> Hello Amir, Luis,
>
> On 2/24/21 5:10 PM, Amir Goldstein wrote:
> > On Wed, Feb 24, 2021 at 4:22 PM Luis Henriques <lhenriques@suse.de> wrote:
> >>
> >> Update man-page with recent changes to this syscall.
> >>
> >> Signed-off-by: Luis Henriques <lhenriques@suse.de>
> >> ---
> >> Hi!
> >>
> >> Here's a suggestion for fixing the manpage for copy_file_range().  Note that
> >> I've assumed the fix will hit 5.12.
> >>
> >>   man2/copy_file_range.2 | 10 +++++++++-
> >>   1 file changed, 9 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
> >> index 611a39b8026b..b0fd85e2631e 100644
> >> --- a/man2/copy_file_range.2
> >> +++ b/man2/copy_file_range.2
> >> @@ -169,6 +169,9 @@ Out of memory.
> >>   .B ENOSPC
> >>   There is not enough space on the target filesystem to complete the copy.
> >>   .TP
> >> +.B EOPNOTSUPP
>
> I'll add the kernel version here:
>
> .BR EOPNOTSUPP " (since Linux 5.12)"

Error could be returned prior to 5.3 and would be probably returned
by future stable kernels 5.3..5.12 too

>
> >> +The filesystem does not support this operation >> +.TP
> >>   .B EOVERFLOW
> >>   The requested source or destination range is too large to represent in the
> >>   specified data types.
> >> @@ -187,7 +190,7 @@ refers to an active swap file.
> >>   .B EXDEV
> >>   The files referred to by
> >>   .IR fd_in " and " fd_out
> >> -are not on the same mounted filesystem (pre Linux 5.3).
> >> +are not on the same mounted filesystem (pre Linux 5.3 and post Linux 5.12).
>
> I'm not sure that 'mounted' adds any value here.  Would you remove the
> word here?

See rename(2). 'mounted' in this context is explained there.
HOWEVER, it does not fit here.
copy_file_range() IS allowed between two mounts of the same filesystem instance.

To make things more complicated, it appears that cross mount clone is not
allowed via FICLONE/FICLONERANGE ioctl, so ioctl_ficlonerange(2) man page
also uses the 'mounted filesystem' terminology for EXDEV

As things stand now, because of the fallback to clone logic,
copy_file_range() provides a way for users to clone across different mounts
of the same filesystem instance, which they cannot do with the FICLONE ioctl.

Fun :)

BTW, I don't know if preventing cross mount clone was done intentionally,
but as I wrote in a comment in the code once:

        /*
         * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
         * the same mount. Practically, they only need to be on the same file
         * system.
         */

>
> It reads as if two separate devices with the same filesystem type would
> still give this error.
>
> Per the LWN.net article Amir shared, this is permitted ("When called
> from user space, copy_file_range() will only try to copy a file across
> filesystems if the two are of the same type").
>
> This behavior was slightly different before 5.3 AFAICR (was it?) ("until
> then, copy_file_range() refused to copy between files that were not
> located on the same filesystem.").  If that's the case, I'd specify the
> difference, or more probably split the error into two, one before 5.3,
> and one since 5.12.
>

True.

> >
> > I think you need to drop the (Linux range) altogether.
>
> I'll keep the range.  Users of 5.3..5.11 might be surprised if the
> filesystems are different and they don't get an error, I think.
>
> I reworded it to follow other pages conventions:
>
> .BR EXDEV " (before Linux 5.3; or since Linux 5.12)"
>
> which renders as:
>
>         EXDEV (before Linux 5.3; or since Linux 5.12)
>                The files referred to by fd_in and fd_out are not on
>                the same mounted filesystem.
>

drop 'mounted'

>
> > What's missing here is the NFS cross server copy use case.
> > Maybe:
> >
> > ...are not on the same mounted filesystem and the source and target filesystems
> > do not support cross-filesystem copy.
>
> Yes.
>
> Again, this wasn't true before 5.3, right?
>

Right.
Actually, v5.3 provides the vfs capabilities for filesystems to support
cross fs copy. I am not sure if NFS already implements cross fs copy in
v5.3 and not sure about cifs. Need to get input from nfs/cis developers
or dig in the release notes for server-side copy.

> >
> > You may refer the reader to VERSIONS section where it will say which
> > filesystems support cross-fs copy as of kernel version XXX (i.e. cifs and nfs).
> >
> >>   .SH VERSIONS
> >>   The
> >>   .BR copy_file_range ()
> >> @@ -202,6 +205,11 @@ Applications should target the behaviour and requirements of 5.3 kernels.
> >>   .PP
> >>   First support for cross-filesystem copies was introduced in Linux 5.3.
> >>   Older kernels will return -EXDEV when cross-filesystem copies are attempted.
> >> +.PP
> >> +After Linux 5.12, support for copies between different filesystems was dropped.
> >> +However, individual filesystems may still provide
> >> +.BR copy_file_range ()
> >> +implementations that allow copies across different devices.
> >
> > Again, this is not likely to stay uptodate for very long.
> > The stable kernels are expected to apply your patch (because it fixes
> > a regression)
> > so this should be phrased differently.
> > If it were me, I would provide all the details of the situation to
> > Michael and ask him
> > to write the best description for this section.
>
> I'll look into more detail at this part in a later review.
>
>
> On 2/26/21 11:34 AM, Amir Goldstein wrote:
>  > Is this detailed enough? ;-)
>  >
>  > https://lwn.net/Articles/846403/
>
> Yes, it is!
>

Thanks to LWN :)

Thanks,
Amir.

  reply	other threads:[~2021-02-27  5:42 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
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 [this message]
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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