On Mon, Aug 26, 2024 at 5:25 PM Alejandro Colomar <alx@xxxxxxxxxx> wrote:
>
> Hi Yafang,
>
> On Sat, Aug 17, 2024 at 10:58:02AM GMT, Alejandro Colomar wrote:
> > Hi Yafang,
> >
> > On Sat, Aug 17, 2024 at 10:56:22AM GMT, Yafang Shao wrote:
> > > These three functions follow the same pattern. To deduplicate the code,
> > > let's introduce a common helper __kmemdup_nul().
> > >
> > > Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > > Cc: Simon Horman <horms@xxxxxxxxxx>
> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > > ---
> > > mm/util.c | 67 +++++++++++++++++++++----------------------------------
> > > 1 file changed, 26 insertions(+), 41 deletions(-)
> > >
> > > diff --git a/mm/util.c b/mm/util.c
> > > index 4542d8a800d9..310c7735c617 100644
> > > --- a/mm/util.c
> > > +++ b/mm/util.c
> > > @@ -45,33 +45,40 @@ void kfree_const(const void *x)
> > > EXPORT_SYMBOL(kfree_const);
> > >
> > > /**
> > > - * kstrdup - allocate space for and copy an existing string
> > > - * @s: the string to duplicate
> > > + * __kmemdup_nul - Create a NUL-terminated string from @s, which might be unterminated.
> > > + * @s: The data to copy
> > > + * @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 or %NULL in case of error
> > > + * Return: newly allocated copy of @s with NUL-termination or %NULL in
> > > + * case of error
> > > */
> > > -noinline
> > > -char *kstrdup(const char *s, gfp_t gfp)
> > > +static __always_inline char *__kmemdup_nul(const char *s, size_t len, gfp_t gfp)
> > > {
> > > - size_t len;
> > > char *buf;
> > >
> > > - if (!s)
> > > + buf = kmalloc_track_caller(len, gfp);
> > > + if (!buf)
> > > 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';
> > > - }
> > > + memcpy(buf, s, len);
> > > + /* Ensure the buf is always NUL-terminated, regardless of @s. */
> > > + buf[len - 1] = '\0';
> > > return buf;
> > > }
> > > +
> > > +/**
> > > + * kstrdup - allocate space for and copy an existing string
> > > + * @s: the string to duplicate
> > > + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> > > + *
> > > + * Return: newly allocated copy of @s or %NULL in case of error
> > > + */
> > > +noinline
> > > +char *kstrdup(const char *s, gfp_t gfp)
> > > +{
> > > + return s ? __kmemdup_nul(s, strlen(s) + 1, gfp) : NULL;
> > > +}
> > > EXPORT_SYMBOL(kstrdup);
> > >
> > > /**
> > > @@ -106,19 +113,7 @@ EXPORT_SYMBOL(kstrdup_const);
> > > */
> > > char *kstrndup(const char *s, size_t max, gfp_t gfp)
> > > {
> > > - size_t len;
> > > - char *buf;
> > > -
> > > - if (!s)
> > > - return NULL;
> > > -
> > > - len = strnlen(s, max);
> > > - buf = kmalloc_track_caller(len+1, gfp);
> > > - if (buf) {
> > > - memcpy(buf, s, len);
> > > - buf[len] = '\0';
> > > - }
> > > - return buf;
> > > + return s ? __kmemdup_nul(s, strnlen(s, max) + 1, gfp) : NULL;
> > > }
> > > EXPORT_SYMBOL(kstrndup);
> > >
> > > @@ -192,17 +187,7 @@ EXPORT_SYMBOL(kvmemdup);
> > > */
> > > char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
> > > {
> > > - char *buf;
> > > -
> > > - if (!s)
> > > - return NULL;
> > > -
> > > - buf = kmalloc_track_caller(len + 1, gfp);
> > > - if (buf) {
> > > - memcpy(buf, s, len);
> > > - buf[len] = '\0';
> > > - }
> > > - return buf;
> > > + return s ? __kmemdup_nul(s, len + 1, gfp) : NULL;
> > > }
> > > EXPORT_SYMBOL(kmemdup_nul);
> >
> > I like the idea of the patch, but it's plagued with all those +1 and -1.
> > I think that's due to a bad choice of value being passed by. If you
> > pass the actual length of the string (as suggested in my reply to the
> > previous patch) you should end up with a cleaner set of APIs.
> >
> > The only remaining +1 is for kmalloc_track_caller(), which I ignore what
> > it does.
> >
> > char *
> > __kmemdup_nul(const char *s, size_t len, gfp_t gfp)
> > {
> > char *buf;
> >
> > buf = kmalloc_track_caller(len + 1, gfp);
> > if (!buf)
> > return NULL;
> >
> > strcpy(mempcpy(buf, s, len), "");
>
> Changing these strcpy(, "") to the usual; ='\0' or =0, but I'd still
> recommend the rest of the changes, that is, changing the value passed in
> len, to remove several +1 and -1s.
>
> What do you think?
I will update it. Thanks for your suggestion.
--
Regards
Yafang
