Re: should copy_file_range(2) have a non-Linux flag?

In reply to: Rick Macklem : "should copy_file_range(2) have a non-Linux flag?"
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From: Crest <crest_at_rlwinm.de>
Date: Mon, 06 Sep 2021 13:21:57 UTC

On 04.09.21 17:08, Rick Macklem wrote:
> Hi,
>
> I just proposed a patch for VOP_COPY_FILE_RANGE(9)
> that adds a kernel only flag to specify "return after 1second
> with a partial copy". I'd like to use it for the NFSv4.2 server,
> so that the RPC replies in a reasonable time frame.
> https://reviews.freebsd.org/D31829
>
> The question that came up is...
> "should this flag be visible to userland?"
>
> The only argument I can think of against doing this is
> that it makes the syscall non-Linux compatible.
> (Also, the NFS server requirement seems a bit of an oddball
>   and I'm not sure an application would want this capability?)
>
> Do you think this flag should be exposed to userland (ie the syscall)?
>
I can see usecases for this flag:

* NFS Ganesha

* Report progress during large file copies e.g. in a git annex special 
remote