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

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Date:	Tue, 14 Apr 2015 13:16:13 -0400
From:	Anna Schumaker <Anna.Schumaker@...app.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Jeff Layton <jlayton@...chiereds.net>
CC:	Trond Myklebust <trond.myklebust@...marydata.com>,
	Zach Brown <zab@...hat.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 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
>> Yuck! How the heck do you clean up the mess if that happens? I guess
>> you're just stuck redoing the copy with normal READ/WRITE?
>>
>> Maybe we need to have the interface return a hard error in that
>> case and not try to give back any sort of offset?
> 
> The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> expect us to simply ignore it and only implement my new CLONE operation
> with sane semantics.  That is unless someone can show some real life
> use case for the inter server copy, in which case we'll have to deal
> with that mess.  But getting that one right at the VFS level will
> be a nightmare anyway.
> 
> Make this a vote from me to not support partial copies and just return
> and error in that case.

Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a ca_synchronous flags that let the client state if the copy should be done consecutively or synchronously.  I expected to always set consecutive to "true" for the Linux client.

Anna

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