Re: Volume management on Linux with the ext2fs.

James Mastros (
Wed, 23 Apr 1997 16:59:01 -0500 (EST)

On 23 Apr 1997, Stefan Monnier wrote:
> Agreed. Actually it recently occured to me that the CacheFS that I'd like Linux
> to support could be (to some point) implemented as an extension of e2fs:
> create a new type of link (let's call it a copylink). When it is accessed, it
> gets replaced by what it points to (and if it was a directory, the directory is
> not copied recursively but filled up with copylinks, of course). The thing
> could later be improved so as to support copying the inode of a remote file
> without the file itself, or even allow to have only some blocks of a remote
> file be copied locally. Also some way to "flush the cache" would be needed
> (or at least some way to rollback copies of files into copylinks so as to
> recover disk space when needed or so as to update remote files that have
> changed)
> Stefan

Implementing copy-on-write for FSes like for memory, basicaly. I thought
of somthing like that when I first heard of copy-on-write; but I wasn't
good enough of a kernel hacker to mention it. I'm still not good enough
of a kernel hacker to even think about doing it, but atleast I'm confident
enough to mention it.

The easyest way to implement it would likely be as a hard link (because it
would act like one on read), but with a flag to be checked during writes.
Fortinataly, it looks like there is plenty of free space in the umode
feild, so we should be able to implement this at a VFS level.

Quite likely wrong,
-=- James Mastros