Re: [PATCH -V19 00/15] Generic name to handle and open by handle syscalls

[Neil Brown <neilb@suse.de>]

On Mon, 13 Sep 2010 08:01:18 +0200
Miklos Szeredi <miklos@szeredi.hu> wrote:

> On Mon, 13 Sep 2010, Aneesh Kumar K. V wrote:
> > As per your suggestion i started looking at handlefs details and below
> > is my take on the approach.
> > 
> > handlefs would be an internal kernel mount like pipefs and would have
> > inode object mapping to the returned file descriptor of
> > open_by_handle_at syscall for symlinks. For regular files we can do what
> > we already does and for symlinks we will create inodes in handlefs and
> > their inode operation will in turn result in call out of inode operations
> > of the actual symlinks. Based on the above
> > 
> > a) We still need open_by_handle_at syscall
> > b) We still need handle based link syscall, because we need to support
> >    creating hardlinks based on handle, and the existing linkat syscall
> >    takes the oldpath name.
> > c) We still need handle based readlink syscall, because the existing
> >    readlinkat syscall takes pathname.
> 
> You can implement ->read() on the symlink file instead.

I would suggest that is a much uglier hack than changed readlinkat to accept
a NULL pathname.

NeilBrown


> 
> > d) we can drop stat, chown and xattr syscall because they are introduced
> >    specially for symlinks as we don't allow open on symlinks.
> > e) It would be nice to have handle based stat syscall to avoid two
> >    syscall overhead for fetching file attributes when implementing a
> >    file server, where fetching file attribute is a common operation. 
> 
> Syscall overhead is generally insignificant compared to other effects.
> The server can also cache open files for commonly used handles.
> 
> > 
> > With the above from the current patch series we can drop chown and
> > xattr syscalls. Would it be ok if we get the series with the those two
> > syscall patches dropped upstream as i work on supporting symlinks with
> > handlefs approach ?
> 
> Try it.
> 
> Al seems to only be active to the outside world around the merge
> window, so that's the best time to ask him to pull.
> 
> Thanks,
> Miklos