Re: [PATCH 1/2] open: add close_range()

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Tue, May 21, 2019 at 08:20:09PM +0100, Al Viro wrote:
> On Tue, May 21, 2019 at 05:30:27PM +0100, David Howells wrote:
> 
> > If we can live with close_from(int first) rather than close_range(), then this
> > can perhaps be done a lot more efficiently by:
> > 
> > 	new = alloc_fdtable(first);
> > 	spin_lock(&files->file_lock);
> > 	old = files_fdtable(files);
> > 	copy_fds(new, old, 0, first - 1);
> > 	rcu_assign_pointer(files->fdt, new);
> > 	spin_unlock(&files->file_lock);
> > 	clear_fds(old, 0, first - 1);
> > 	close_fdt_from(old, first);
> > 	kfree_rcu(old);
> 
> I really hate to think how that would interact with POSIX locks...

POSIX locks store current->files in fl_owner; David's resizing the
underlying files->fdt, just like growing from 64 to 256 fds.