Re: RFC: case-insensitive rename support in the VFS

[Christoph Hellwig <hch@infradead.org>]

On Fri, May 02, 2008 at 02:14:56PM +1000, Barry Naujok wrote:
> As some of you know, I've been working on CI support for XFS.
> Currently, the Linux VFS does not make this very easy and neat.
>
> One issue I've encountered is the case of rename in a CI
> filesystem where the destination is the same as the source
> (both parent and child) differing only in case.
>
> So, currently, do_rename() calls do_path_lookup() which
> gets the source and destination dentries, etc. The third
> parameter, flags, is stored in the nameidata structure
> which is passed to the filesystem implementations of
> lookup.
>
> vfs_rename() checks to see if the two dentry inodes are
> the same, and if so, just returns 0.
>
> I propose adding a 7th LOOKUP_xxx flag for the rename case
> where we indicate we are after an exact (non-CI) match for
> the destination name in the lookup call in do_rename.
>
> Filesystem support in lookup would check for this flag
> in addition to LOOKUP_CONTINUE not existing (ie. at the
> last component during lookup) and if so, do an exact
> lookup rather than a CI lookup as it normally would do.
> Traditional non-CI filesystems would ignore this flag.

I think passing a flag to the filesystem for this is fine, but
flag in nameidata won't do it since lookup is going to lose the
nameidata argument soon.