Overwriting copy functionality in filesystem

[Bharath Vedartham]

On Sat, Mar 23, 2019 at 08:03:20PM +0100, Bernd Petrovitsch wrote:
> Hi all!
> 
> On 23/03/2019 17:59, Bharath Vedartham wrote:
> [..]
> > I was wondering how we can overwrite the copy functionality while
> > writing our own filesystem in linux. 
> > VFS does not offer any sort of API for copy. I think it calls create and
> 
> Yes.
> 
> > write when we execute the copy the file/dir.
> > I am interested in overwriting the way copy happens in my
> > filesystem(which I am writing for fun :p). 
> > Any ideas?
> 
> strace a "cp" and see which system calls are used.
> Look into the source code and see how it's implemented.
> 
> There is actually more than one method but the usual (while simplest,
> most versatile and probably fastest) method used is: open source and
> destination files, read from the source, write into the destination
> until EOF.
>
I have observed that it is a mixture of system calls. I am interested in
implementing copy-on-write in my filesystem(for fun). I feel that, it
would require my creat vfs api to be aware of the fact that "cp" is
calling it. I want to keep things as generic as possible. I ll proceed
by reading the source of union filesystems (overlayfs) to see how they
implement copy-on-write.
> MfG,
> 	Bernd
> -- 
> Bernd Petrovitsch                  Email : bernd at petrovitsch.priv.at
>                      LUGA : http://www.luga.at