From: Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>
To: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Cc: "Darrick J. Wong"
<darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>,
"Pádraig Brady" <P@draigbrady.com>,
"Anna Schumaker"
<Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>,
linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
"Linux btrfs Developers List"
<linux-btrfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Linux FS Devel"
<linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Linux API" <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Zach Brown" <zab-ugsP4Wv/S6ZeoWH0uzbU5w@public.gmane.org>,
"Al Viro"
<viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
"Chris Mason" <clm-b10kYP2dOMg@public.gmane.org>,
"Michael Kerrisk-manpages"
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
andros-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org,
"Christoph Hellwig" <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
Coreutils <coreutils-mXXj517/zsQ@public.gmane.org>
Subject: Re: [PATCH v1 0/8] VFS: In-kernel copy system call
Date: Mon, 14 Sep 2015 09:25:29 +1000 [thread overview]
Message-ID: <20150913232529.GT26895@dastard> (raw)
In-Reply-To: <CALCETrVsWBdqvAgwxHcG=gbcWRNPG2ZziWUg1g=siKDrDu7S2Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
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...
Cheers,
Dave.
--
Dave Chinner
david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org
next prev parent reply other threads:[~2015-09-13 23:25 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
[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 [this message]
2015-09-14 17:53 ` Andy Lutomirski
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 20:16 ` [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
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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