Re: New copyfile system call - discuss before LSF?

Andreas Dilger
2013-03-30T20:08:47Z

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