Re: [fuse-devel] COW support (BTRFS_IOC_CLONE)

[Nikolaus R. <Nik...@ra...>]

Goswin von Brederlow <gos...@we...> writes:
> Hi,
>
> at some point in recent history the cp utility has learned
>
>        --reflink[=WHEN]
>               control clone/CoW copies. See below.
>
>        When --reflink[=always] is specified, perform a lightweight copy,
>        where the data blocks are copied only when modified.  If this is
>        not possible the copy fails, or if --reflink=auto is specified,
>        fall back to a stan- dard copy.
>
> This is done using an ioctl of BTRFS_IOC_CLONE and, for any FS with COW
> capability, makes copying a lot faster and space efficient.
>
>
> I'm wondering if I can implement this in fuse with the ioctl callback?
> Anyone knowlegable in that regard?

I don't have any knowledge about this yet either, but I am very much
interested.

Currently, my file system comes with its own implementation of a cp
command that does lightweight copying by communicating with the FS over
extended attributes on a special invisible control file that resides in
every directory.

Please keep us posted if you learn more about the ioctl. It'd be nice to
have this functionality standardized. 


Best,


   -Nikolaus

-- 
 »Time flies like an arrow, fruit flies like a Banana.«

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