From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
To: Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>
Cc: "Zach Brown" <zab-ugsP4Wv/S6ZeoWH0uzbU5w@public.gmane.org>,
Coreutils <coreutils-mXXj517/zsQ@public.gmane.org>,
"Al Viro"
<viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
"Anna Schumaker"
<Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>,
andros-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org,
"Darrick J. Wong"
<darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>,
"Pádraig Brady" <P@draigbrady.com>,
"Linux btrfs Developers List"
<linux-btrfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Chris Mason" <clm-b10kYP2dOMg@public.gmane.org>,
"Linux API" <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Christoph Hellwig" <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
"Michael Kerrisk-manpages"
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
"Linux FS Devel"
<linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v1 0/8] VFS: In-kernel copy system call
Date: Mon, 14 Sep 2015 10:53:23 -0700 [thread overview]
Message-ID: <CALCETrUALh=tiK9S0LhvJuy4jK-1vk5bjnz2b0faWhw0mSLs=g@mail.gmail.com> (raw)
In-Reply-To: <20150913232529.GT26895@dastard>
On Sep 13, 2015 4:25 PM, "Dave Chinner" <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org> wrote:
>
> On Tue, Sep 08, 2015 at 04:08:43PM -0700, Andy Lutomirski wrote:
> > Can we have a clean way to figure out whether two file ranges are the
> > same in a way that allows false negatives? I.e. return 1 if the
> > ranges are reflinks of each other and 0 if not? Pretty please? I've
> > implemented that in the past on btrfs by syncing the ranges and then
> > comparing FIEMAP output, but that's hideous.
>
> That fundamentally doesn't work for userspace, because the moment
> the filesystem drops it's locks on the inodes in the kernel after
> doing the comparison the mappings can change. IOWs, by the time the
> information gets back to userspace, it's already wrong. e.g. cp made
> this mistake by trying to use FIEMAP to optimise hole detection in
> files and ended up with corrupt copies.
>
> It really doesn't matter what the syscall/ioctl interface is, trying
> to make application logic decisions based on inode block mappings
> from userspace is racy and not safe and will go wrong...
>
I agree, and that thing was just an experiment. I'd love to see a
sane and correct interface, though.
--Andy
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next prev parent reply other threads:[~2015-09-14 17:53 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-04 20:16 [PATCH v1 0/8] VFS: In-kernel copy system call Anna Schumaker
2015-09-04 20:16 ` [PATCH v1 2/8] x86: add sys_copy_file_range to syscall tables Anna Schumaker
2015-09-04 20:16 ` [PATCH v1 3/8] btrfs: add .copy_file_range file operation Anna Schumaker
[not found] ` <1441397823-1203-4-git-send-email-Anna.Schumaker-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-04 21:02 ` Josef Bacik
2015-09-09 8:39 ` David Sterba
[not found] ` <1441397823-1203-1-git-send-email-Anna.Schumaker-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-04 20:16 ` [PATCH v1 1/9] vfs: add copy_file_range syscall and vfs helper Anna Schumaker
2015-09-04 21:50 ` Darrick J. Wong
2015-09-04 20:16 ` [PATCH v1 4/8] btrfs: Add mountpoint checking during btrfs_copy_file_range Anna Schumaker
2015-09-09 9:18 ` David Sterba
2015-09-09 15:56 ` Anna Schumaker
2015-09-04 20:16 ` [PATCH v1 5/8] vfs: Remove copy_file_range mountpoint checks Anna Schumaker
2015-09-04 20:17 ` [PATCH v1 6/8] vfs: Copy should check len after file open mode Anna Schumaker
2015-09-04 20:17 ` [PATCH v1 8/8] vfs: Fall back on splice if no copy function defined Anna Schumaker
2015-09-04 21:08 ` Darrick J. Wong
[not found] ` <20150904210813.GA30681-PTl6brltDGh4DFYR7WNSRA@public.gmane.org>
2015-09-08 14:57 ` Anna Schumaker
2015-09-04 20:17 ` [PATCH v1 9/8] copy_file_range.2: New page documenting copy_file_range() Anna Schumaker
2015-09-04 21:38 ` Darrick J. Wong
[not found] ` <20150904213856.GC10391-PTl6brltDGh4DFYR7WNSRA@public.gmane.org>
2015-09-04 22:31 ` Andreas Dilger
[not found] ` <95674806-645C-410C-8A4B-A46F03AFFE20-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>
2015-09-08 15:05 ` Anna Schumaker
2015-09-08 15:04 ` Anna Schumaker
2015-09-08 20:39 ` Darrick J. Wong
2015-09-09 9:16 ` David Sterba
[not found] ` <20150908203918.GB30681-PTl6brltDGh4DFYR7WNSRA@public.gmane.org>
2015-09-09 11:38 ` Austin S Hemmelgarn
2015-09-09 17:17 ` Darrick J. Wong
[not found] ` <20150909171757.GE10391-PTl6brltDGh4DFYR7WNSRA@public.gmane.org>
2015-09-09 17:31 ` Anna Schumaker
[not found] ` <55F06CEC.5040208-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-09 18:12 ` Darrick J. Wong
2015-09-09 19:25 ` Anna Schumaker
2015-09-10 15:42 ` David Sterba
[not found] ` <20150910154251.GM8891-1ReQVI26iDCaZKY3DrU6dA@public.gmane.org>
2015-09-10 16:43 ` Darrick J. Wong
2015-09-04 22:25 ` [PATCH v1 0/8] VFS: In-kernel copy system call Andreas Dilger
[not found] ` <4B41043F-5D85-42D6-8F20-2DCC45930EF4-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>
2015-09-05 8:33 ` Al Viro
[not found] ` <20150905083342.GG22011-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2015-09-08 15:08 ` Anna Schumaker
2015-09-08 20:45 ` Darrick J. Wong
[not found] ` <20150908204517.GC30681-PTl6brltDGh4DFYR7WNSRA@public.gmane.org>
2015-09-08 20:49 ` Anna Schumaker
2015-09-08 15:07 ` Anna Schumaker
2015-09-08 15:21 ` Pádraig Brady
[not found] ` <55EEFCEE.5090000-V8g9lnOeT5ydJdNcDFJN0w@public.gmane.org>
2015-09-08 18:23 ` Anna Schumaker
[not found] ` <55EF279B.3020101-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-08 19:10 ` Andy Lutomirski
[not found] ` <CALCETrXxRB-LXVb+=nkwfj0zEjWuXXTctkSAc9Oec0fgyOQ5Yg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-09-08 20:03 ` Pádraig Brady
[not found] ` <55EF3EFD.3080302-V8g9lnOeT5ydJdNcDFJN0w@public.gmane.org>
2015-09-08 21:29 ` Darrick J. Wong
2015-09-08 21:45 ` Andy Lutomirski
2015-09-08 22:39 ` Darrick J. Wong
2015-09-08 23:08 ` Andy Lutomirski
2015-09-09 1:19 ` Darrick J. Wong
2015-09-09 20:09 ` Chris Mason
[not found] ` <20150909200921.GD9511-DzB2rL6jT1BHfPKRx072akEOCMrvLtNR@public.gmane.org>
2015-09-09 20:26 ` Trond Myklebust
[not found] ` <CAHQdGtTSZ1beMMF4DJv=OuA1j2ww0xzJj3+9HMRAf3UpCCLaZg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-09-09 20:38 ` Chris Mason
[not found] ` <20150909203805.GE9511-DzB2rL6jT1BHfPKRx072akEOCMrvLtNR@public.gmane.org>
2015-09-09 20:41 ` Anna Schumaker
[not found] ` <55F0997E.1040105-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-09 21:42 ` Darrick J. Wong
2015-09-09 20:37 ` Andy Lutomirski
[not found] ` <CALCETrXPcxHWGwqhtkGStVabWDOsRbBy+VzrN+XxVZA_F9O0qA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-09-09 20:42 ` Chris Mason
[not found] ` <CALCETrVsWBdqvAgwxHcG=gbcWRNPG2ZziWUg1g=siKDrDu7S2Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-09-13 23:25 ` Dave Chinner
2015-09-14 17:53 ` Andy Lutomirski [this message]
2015-09-09 18:52 ` Anna Schumaker
[not found] ` <55F07FD8.4020507-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-09 21:16 ` Darrick J. Wong
2015-09-10 15:10 ` Anna Schumaker
[not found] ` <55F19D7F.5090907-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
2015-09-10 15:49 ` Austin S Hemmelgarn
2015-09-10 11:40 ` Austin S Hemmelgarn
2015-09-04 20:17 ` [PATCH v1 7/8] vfs: Copy should use file_out rather than file_in Anna Schumaker
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