linux-kernel - Re: [PATCH RFC 1/3] vfs: add copy_file

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Message-ID: <20150414192325.GB20599@infradead.org>
Date:	Tue, 14 Apr 2015 12:23:25 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Zach Brown <zab@...hat.com>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	Anna Schumaker <Anna.Schumaker@...app.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
	linux-btrfs@...r.kernel.org,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH RFC 1/3] vfs: add copy_file_range syscall and vfs helper

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.
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