Re: COW files

[Lexington Luthor <Lexington.Luthor@gmail.com>]

David Masover wrote:
> Ok, are you talking about making all the files COW, or the directory
> structure itself somehow COW?
> 
> Because if someone patched "cp" to do COW files, I'm sure it would also
> work for "cp -a", which would be about as fast as "cp -al".
> 
> I'm not sure how it'd work to make entire directories COW -- that is,
> "cp -a" is as fast as "ln" of a single file.
> 
> 
> And before anyone from LKML gets any funny ideas, there's no reason why
> COW should be Reiser4 specific.  We've been due a "copy" system call for
> at least a decade.  Why not just add that, with the realization that
> POSIX would be brain-dead not to add support for it later, then make it
> COW for FS-es that support it, and a simple copy for FS-es that don't.
> 
> With any luck, not a line of any non-COW FS need be changed to support
> the copy system call, unless they want to add COW support as well.
> 
> And if you think it's bad copying a couple of gigs around on a local
> hard disk, wishing it could copy-on-write, try an NFS mount over a
> (very) long-distance VPN.  Why should cp send a couple of gigs across a
> network and back, when the machine running the "cp" command never needs
> to see it?
> 

I would not mind this being reiser4 specific, I don't use the archaic 
filesystems much, they are far too slow compared to reiser4.

As for the exact semantics of COW, whether it applies to file or to 
entire directories, I don't really care as long as it is fast. At the 
moment, the userspace library makes things very fast, but very 
inconvenient since I need to spawn a new shell in the hard-linked tree, 
and while screen + zsh and its history sharing makes that bearable, its 
still a PITA.

LL