Re: [PATCH v3 06/11] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}

Yafang Shao
2024-06-23T02:26:50Z

On Fri, Jun 21, 2024 at 9:51 PM Simon Horman <horms@kernel.org> wrote:
>
> On Fri, Jun 21, 2024 at 10:29:54AM +0800, Yafang Shao wrote:
> > These three functions follow the same pattern. To deduplicate the code,
> > let's introduce a common help __kstrndup().
> >
> > Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
>
> Hi Yafang Shao,
>
> Some minor nits from my side.
>
> > ---
> > mm/internal.h | 24 ++++++++++++++++++++++++
> > mm/util.c | 27 ++++-----------------------
> > 2 files changed, 28 insertions(+), 23 deletions(-)
> >
> > diff --git a/mm/internal.h b/mm/internal.h
> > index b2c75b12014e..fd87f685739b 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -1521,4 +1521,28 @@ static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
> > void workingset_update_node(struct xa_node *node);
> > extern struct list_lru shadow_nodes;
> >
> > +/**
> > + * __kstrndup - Create a NUL-terminated string from @s, which might be unterminated.
> > + * @s: The data to stringify
> > + * @len: The size of the data, including the null terminator
> > + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> > + *
> > + * Return: newly allocated copy of @s with NUL-termination or %NULL in
> > + * case of error
> > + */
> > +static __always_inline char *__kstrndup(const char *s, size_t len, gfp_t gfp)
> > +{
> > + char *buf;
> > +
> > + buf = kmalloc_track_caller(len, gfp);
> > + if (!buf)
> > + return NULL;
> > +
> > + memcpy(buf, s, len);
> > + /* Ensure the buf is always NUL-terminated, regardless of @s. */
> > + buf[len - 1] = '\0';
> > + return buf;
> > +}
> > +
> > +
>
> nit: One blank line is enough.

Ah, will change it.

>
> > #endif /* __MM_INTERNAL_H */
> > diff --git a/mm/util.c b/mm/util.c
> > index 41c7875572ed..d9135c5fdf7f 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -58,17 +58,8 @@ char *kstrdup(const char *s, gfp_t gfp)
> > if (!s)
> > return NULL;
> >
> > - len = strlen(s) + 1;
> > - buf = kmalloc_track_caller(len, gfp);
> > - if (buf) {
> > - memcpy(buf, s, len);
> > - /* During memcpy(), the string might be updated to a new value,
> > - * which could be longer than the string when strlen() is
> > - * called. Therefore, we need to add a null termimator.
> > - */
> > - buf[len - 1] = '\0';
> > - }
> > - return buf;
>
> nit: The local variable buf is now unused, and should be removed from kstrdup().
> Likewise for kstrndup() and kmemdup_nul()
>
> Flagged by W=1 builds with gcc-13 and clang-18, and Smatch.

I missed that. Thanks for pointing it out.

--
Regards
Yafang