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Re: [PATCH v1 0/8] VFS: In-kernel copy system call
From: |
Andy Lutomirski |
Subject: |
Re: [PATCH v1 0/8] VFS: In-kernel copy system call |
Date: |
Mon, 14 Sep 2015 10:53:23 -0700 |
On Sep 13, 2015 4:25 PM, "Dave Chinner" <address@hidden> 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
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, (continued)
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Andy Lutomirski, 2015/09/08
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Darrick J. Wong, 2015/09/08
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Chris Mason, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Trond Myklebust, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Chris Mason, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Anna Schumaker, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Darrick J. Wong, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Andy Lutomirski, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Chris Mason, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Dave Chinner, 2015/09/13
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call,
Andy Lutomirski <=
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Anna Schumaker, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Darrick J. Wong, 2015/09/09
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Anna Schumaker, 2015/09/10
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Austin S Hemmelgarn, 2015/09/10
- Re: [PATCH v1 0/8] VFS: In-kernel copy system call, Austin S Hemmelgarn, 2015/09/10