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SubjectRe: [PATCH 2/3] fat: add the msdos_format_name() filename cache
On Sun, Aug 29, 2021 at 03:11:22PM +0000, Al Viro wrote:
> On Sun, Aug 29, 2021 at 02:25:29PM +0000, Caleb D.S. Brzezinski wrote:
> > Implement the main msdos_format_name() filename cache. If used as a
> > module, all memory allocated for the cache is freed when the module is
> > de-registered.
> >
> > Signed-off-by: Caleb D.S. Brzezinski <calebdsb@protonmail.com>
> > ---
> > fs/fat/namei_msdos.c | 35 +++++++++++++++++++++++++++++++++++
> > 1 file changed, 35 insertions(+)
> >
> > diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
> > index 7561674b1..f9d4f63c3 100644
> > --- a/fs/fat/namei_msdos.c
> > +++ b/fs/fat/namei_msdos.c
> > @@ -124,6 +124,16 @@ static int msdos_format_name(const unsigned char *name, int len,
> > unsigned char *walk;
> > unsigned char c;
> > int space;
> > + u64 hash;
> > + struct msdos_name_node *node;
> > +
> > + /* check if the name is already in the cache */
> > +
> > + hash = msdos_fname_hash(name);
> > + if (find_fname_in_cache(res, hash))
> > + return 0;
>
> Huh? How could that possibly work, seeing that
> * your hash function only looks at the first 8 characters
> * your find_fname_in_cache() assumes that hash collisions
> are impossible, which is... unlikely, considering the nature of
> that hash function
> * find_fname_in_cache(res, hash) copies at most 8 characters
> into res in case of match. Where does the extension come from?
>
> Out of curiosity, how have you tested that thing?

While we are at it, your "fast path" doesn't even look at opts
argument...

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