Re: [PATCH] fs: allow do_renameat2() over bind mounts of the same filesystem.

Matthew Wilcox
2020-08-29T22:12:13Z

On Sat, Aug 29, 2020 at 11:23:34PM +0200, Florian Margaine wrote:
> Al Viro <viro@zeniv.linux.org.uk> writes:
>
> > On Fri, Aug 28, 2020 at 10:40:35PM +0200, Florian Margaine wrote:
> >> There's currently this seemingly unnecessary limitation that rename()
> >> cannot work over bind mounts of the same filesystem,
> >
> > ... is absolutely deliberate - that's how you set a boundary in the
> > tree, preventing both links and renames across it.
>
> Sorry, I'm not not sure I understand what you're saying.

Al's saying this is the way an administrator can intentionally prevent
renames.

> /*
> * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
> * the same mount. Practically, they only need to be on the same file
> * system.
> */
> if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> return -EXDEV;

clone doesn't change the contents of a file, merely how they're laid out
on storage. There's no particular reason for an administrator to
prohibit clone across mount points.