Re: New copyfile system call - discuss before LSF?

Pádraig Brady
2013-03-31T11:48:42Z

On 03/30/2013 08:08 PM, Andreas Dilger wrote:
> On 2013-03-30, at 12:49 PM, Pavel Machek wrote:
>> Hmm, really? AFAICT it would be simple to provide an
>> open_deleted_file("directory") syscall. You'd open_deleted_file(),
>> copy source file into it, then fsync(), then link it into filesystem.
>>
>> That should have atomicity properties reflected.
>
> Actually, the open_deleted_file() syscall is quite useful for many
> different things all by itself. Lots of applications need to create
> temporary files that are unlinked at application failure (without a
> race if app crashes after creating the file, but before unlinking).
> It also avoids exposing temporary files into the namespace if other
> applications are accessing the directory.
>
> We've added a library routine that does this for Lustre in a hackish
> way (magical filename created in target directory) for being able to
> migrate files between data servers, HSM, defragmentation, rsync, etc.
>
> Cheers, Andreas

This reminds me of the flink() discussion:
http://marc.info/?l=linux-kernel&m=104965452917349

Also kinda related is the exchangedata() OSX system call to
"atomically exchange data between two files"

thanks,
Pádraig.