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b=uHZuxKobkZPexs4wQXgy+BigHynUnVn2wGZXIYK3rG4h1ghhRi91iSqYmk1RnU63k MYVCdI6WXmjOKe7vXj9nBcdZr2YbbrM+4cxYpWJnBOzHYN8WBZYmnx6wTiP4pjScM+ a/38aDduZcDlZxZVablIYLfBKHjroH/uEmZroFJijBXpSek36A1Vq0124G01TH8w0V 349jwsrENGcMoLN4tKqn/Ly5mzH+uaU1bEjYR6cmhq5vnxcfuxX9XmftRtil9AjQ5X ZZp+c56fp7/mSI3ovhzAorNflOdFGMQvkdTuHSISLpP32Gg7Nqy6zjelHnwHbFIEv+ WQ4Hzf798ofiA== Date: Sat, 17 Aug 2024 11:05:06 +0200 From: Alejandro Colomar To: Yafang Shao Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, justinstitt@google.com, ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, catalin.marinas@arm.com, penguin-kernel@i-love.sakura.ne.jp, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, audit@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, Simon Horman , Matthew Wilcox Subject: Re: [PATCH v7 6/8] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul} Message-ID: References: <20240817025624.13157-1-laoar.shao@gmail.com> <20240817025624.13157-7-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; 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protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable From: Alejandro Colomar To: Yafang Shao Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, justinstitt@google.com, ebiederm@xmission.com, alexei.starovoitov@gmail.com, rostedt@goodmis.org, catalin.marinas@arm.com, penguin-kernel@i-love.sakura.ne.jp, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, audit@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, Simon Horman , Matthew Wilcox Subject: Re: [PATCH v7 6/8] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul} References: <20240817025624.13157-1-laoar.shao@gmail.com> <20240817025624.13157-7-laoar.shao@gmail.com> MIME-Version: 1.0 In-Reply-To: On Sat, Aug 17, 2024 at 10:58:02AM GMT, Alejandro Colomar wrote: > Hi Yafang, >=20 > 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(). > >=20 > > Suggested-by: Andrew Morton > > Signed-off-by: Yafang Shao > > Cc: Simon Horman > > Cc: Matthew Wilcox > > --- > > mm/util.c | 67 +++++++++++++++++++++---------------------------------- > > 1 file changed, 26 insertions(+), 41 deletions(-) > >=20 > > 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); > > =20 > > /** > > - * 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; > > =20 > > - if (!s) > > + buf =3D kmalloc_track_caller(len, gfp); > > + if (!buf) > > return NULL; > > =20 > > - len =3D strlen(s) + 1; > > - buf =3D 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] =3D '\0'; > > - } > > + memcpy(buf, s, len); > > + /* Ensure the buf is always NUL-terminated, regardless of @s. */ > > + buf[len - 1] =3D '\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); > > =20 > > /** > > @@ -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 =3D strnlen(s, max); > > - buf =3D kmalloc_track_caller(len+1, gfp); > > - if (buf) { > > - memcpy(buf, s, len); > > - buf[len] =3D '\0'; > > - } > > - return buf; > > + return s ? __kmemdup_nul(s, strnlen(s, max) + 1, gfp) : NULL; > > } > > EXPORT_SYMBOL(kstrndup); > > =20 > > @@ -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 =3D kmalloc_track_caller(len + 1, gfp); > > - if (buf) { > > - memcpy(buf, s, len); > > - buf[len] =3D '\0'; > > - } > > - return buf; > > + return s ? __kmemdup_nul(s, len + 1, gfp) : NULL; > > } > > EXPORT_SYMBOL(kmemdup_nul); >=20 > 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. >=20 > The only remaining +1 is for kmalloc_track_caller(), which I ignore what > it does. D'oh, of course that's the malloc. Yes, it makes sense to have a +1 there. >=20 > char * > __kmemdup_nul(const char *s, size_t len, gfp_t gfp) > { > char *buf; >=20 > buf =3D kmalloc_track_caller(len + 1, gfp); > if (!buf) > return NULL; >=20 > strcpy(mempcpy(buf, s, len), ""); > return buf; Alternatively, you can also rewrite the above two lines into one as: return strncat(strcpy(buf, ""), s, len); The good thing is that you have strncat() in the kernel, AFAICS. I reminded myself when checking the definitions that I wrote in shadow: #define XSTRNDUP(s) \ ( \ STRNCAT(strcpy(XMALLOC(strnlen(s, NITEMS(s)) + 1, char), ""), s) \ ) #define STRNDUPA(s) \ ( \ STRNCAT(strcpy(alloca(strnlen(s, NITEMS(s)) + 1), ""), s) \ ) Cheers, Alex > } >=20 > char * > kstrdup(const char *s, gfp_t gfp) > { > return s ? __kmemdup_nul(s, strlen(s), gfp) : NULL; > } >=20 > char * > kstrndup(const char *s, size_t n, gfp_t gfp) > { > return s ? __kmemdup_nul(s, strnlen(s, n), gfp) : NULL; > } >=20 > char * > kmemdup_nul(const char *s, size_t len, gfp_t gfp) > { > return s ? __kmemdup_nul(s, len, gfp) : NULL; > } >=20 > Have a lovely day! > Alex >=20 > --=20 > --=20 --4u7yqqf3o53fozhu Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEE6jqH8KTroDDkXfJAnowa+77/2zIFAmbAZ8IACgkQnowa+77/ 2zLvOA//Z/lDWnXjHMZFqj20EeCk/sOJvw2j0zS6ByjjhPwbF0QB4deovmQwO1rB UfUFQNBO+A+m7nw8x/mLrYWRp9QX1koU8+XGacYS2fA/3zREzEbEDkWgaRej0TkD lI5oQJysXdRk4zv0t+oSPS42Ga+OLoqOogKapp40DpFcY/PfC0lI/dP32nYeKIpL H6XRqcEwqTOSNl8LOg3YkNO6Z93l+zsqDRCeiqze77O0QnrxDYY5gZdQkBfTiWDv w5CzMOKn55JzbPrbPiQID2PKvokrMvtE0cS6WpBOjLNguoEyrPWaOJY9wTe3zJx0 jYczxxaqMVJOy+e/JzejKO7/8UaL4BjsKRkQxDUqX9JT2M1Mx94U/x4NdJ74Qpjg BT5tAy0REvgQ5nfchZzwMxj94NK8fQ1kls54V3RcZ4SwF8Y8TL/UIXO0n3OHbHAZ dDSam/sQaJCtIDEfeSjIAMISt2mUPaSu+K9IUQl5xlL+7hvtP7YJzOy0W5cP87uT OIswibfrvvKaeBSmpPx2reAdydjV0ErJia59TA8Qr1gbtFl5N4y6V6KCAojgjKL/ RMowH5Jeai7WuTHla5CCBRc9sSpx2BFHpdcfW1+Kt8SvhOQ9BOcEq42xaM2megcd weFqBQ6+YsgwWcVz7UNoMIi2UfQQpAvIflidVV9krOZsjk3OT9s= =BouQ -----END PGP SIGNATURE----- --4u7yqqf3o53fozhu--