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Date: Tue, 14 Apr 2015 12:23:25 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Zach Brown <zab@redhat.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
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Subject: Re: [PATCH RFC 1/3] vfs: add copy_file_range syscall and vfs helper
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On Tue, Apr 14, 2015 at 11:54:08AM -0700, Zach Brown wrote:
> Is this relying on btrfs range cloning being atomic?  It certainly
> doesn't look atomic.  It can modify items across an arbitrarily large
> number of leaf blocks.  It can make the changes across multiple
> transactions which could introduce partial modification on reboot after
> crashes.  It can fail (the dynamic duo: enomem, eio) and leave the
> desintation partially modified.

I didn't mean atomic in the failure atomic sense, but in the sense of
being atomic vs other writes, similar to how Posix specifies it for
writes vs other writes.  Guess I need to express this intent better.