[PATCH net-next v1 1/2] string: Make memscan() to take const

[PATCH net-next v1 1/2] string: Make memscan() to take const

[Andy Shevchenko]

Make memscan() to take const so it will be easier replace
some memchr() cases with it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 arch/s390/include/asm/string.h          | 4 ++--
 arch/s390/lib/string.c                  | 2 +-
 arch/sparc/include/asm/asm-prototypes.h | 4 ++--
 arch/sparc/include/asm/string.h         | 7 ++++---
 arch/x86/include/asm/string_32.h        | 2 +-
 arch/x86/lib/string_32.c                | 2 +-
 include/linux/string.h                  | 2 +-
 lib/string.c                            | 2 +-
 8 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/arch/s390/include/asm/string.h b/arch/s390/include/asm/string.h
index 3fae93ddb322..0196fd466a39 100644
--- a/arch/s390/include/asm/string.h
+++ b/arch/s390/include/asm/string.h
@@ -120,7 +120,7 @@ static inline void *memchr(const void * s, int c, size_t n)
 #endif
 
 #ifdef __HAVE_ARCH_MEMSCAN
-static inline void *memscan(void *s, int c, size_t n)
+static inline void *memscan(const void *s, int c, size_t n)
 {
 	const void *ret = s + n;
 
@@ -205,7 +205,7 @@ static inline size_t strnlen(const char * s, size_t n)
 #endif
 #else /* IN_ARCH_STRING_C */
 void *memchr(const void * s, int c, size_t n);
-void *memscan(void *s, int c, size_t n);
+void *memscan(const void *s, int c, size_t n);
 char *strcat(char *dst, const char *src);
 char *strcpy(char *dst, const char *src);
 size_t strlen(const char *s);
diff --git a/arch/s390/lib/string.c b/arch/s390/lib/string.c
index 7d8741818239..ec9786fde1dd 100644
--- a/arch/s390/lib/string.c
+++ b/arch/s390/lib/string.c
@@ -331,7 +331,7 @@ EXPORT_SYMBOL(memcmp);
  * the area if @c is not found
  */
 #ifdef __HAVE_ARCH_MEMSCAN
-void *memscan(void *s, int c, size_t n)
+void *memscan(const void *s, int c, size_t n)
 {
 	const void *ret = s + n;
 
diff --git a/arch/sparc/include/asm/asm-prototypes.h b/arch/sparc/include/asm/asm-prototypes.h
index 4987c735ff56..3a82a86a27a6 100644
--- a/arch/sparc/include/asm/asm-prototypes.h
+++ b/arch/sparc/include/asm/asm-prototypes.h
@@ -13,8 +13,8 @@
 #include <asm/oplib.h>
 #include <linux/atomic.h>
 
-void *__memscan_zero(void *, size_t);
-void *__memscan_generic(void *, int, size_t);
+void *__memscan_zero(const void *, size_t);
+void *__memscan_generic(const void *, int, size_t);
 void *__bzero(void *, size_t);
 void VISenter(void); /* Dummy prototype to supress warning */
 #undef memcpy
diff --git a/arch/sparc/include/asm/string.h b/arch/sparc/include/asm/string.h
index 001a17baf2d5..7761a037b377 100644
--- a/arch/sparc/include/asm/string.h
+++ b/arch/sparc/include/asm/string.h
@@ -21,10 +21,11 @@ void *memmove(void *, const void *, __kernel_size_t);
 
 #define memscan(__arg0, __char, __arg2)						\
 ({										\
-	void *__memscan_zero(void *, size_t);					\
-	void *__memscan_generic(void *, int, size_t);				\
-	void *__retval, *__addr = (__arg0);					\
+	void *__memscan_zero(const void *, size_t);				\
+	void *__memscan_generic(const void *, int, size_t);			\
+	const void *__addr = (__arg0);						\
 	size_t __size = (__arg2);						\
+	void *__retval;								\
 										\
 	if(__builtin_constant_p(__char) && !(__char))				\
 		__retval = __memscan_zero(__addr, __size);			\
diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
index 32c0d981a82a..30245f7707e7 100644
--- a/arch/x86/include/asm/string_32.h
+++ b/arch/x86/include/asm/string_32.h
@@ -223,7 +223,7 @@ static inline void *memset32(uint32_t *s, uint32_t v, size_t n)
  * find the first occurrence of byte 'c', or 1 past the area if none
  */
 #define __HAVE_ARCH_MEMSCAN
-extern void *memscan(void *addr, int c, size_t size);
+extern void *memscan(const void *addr, int c, size_t size);
 
 #endif /* __KERNEL__ */
 
diff --git a/arch/x86/lib/string_32.c b/arch/x86/lib/string_32.c
index 53b3f202267c..4124d6678f72 100644
--- a/arch/x86/lib/string_32.c
+++ b/arch/x86/lib/string_32.c
@@ -198,7 +198,7 @@ EXPORT_SYMBOL(memchr);
 #endif
 
 #ifdef __HAVE_ARCH_MEMSCAN
-void *memscan(void *addr, int c, size_t size)
+void *memscan(const void *addr, int c, size_t size)
 {
 	if (!size)
 		return addr;
diff --git a/include/linux/string.h b/include/linux/string.h
index c062c581a98b..a7bff7ed3cb0 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -150,7 +150,7 @@ extern void * memcpy(void *,const void *,__kernel_size_t);
 extern void * memmove(void *,const void *,__kernel_size_t);
 #endif
 #ifndef __HAVE_ARCH_MEMSCAN
-extern void * memscan(void *,int,__kernel_size_t);
+extern void * memscan(const void *,int,__kernel_size_t);
 #endif
 #ifndef __HAVE_ARCH_MEMCMP
 extern int memcmp(const void *,const void *,__kernel_size_t);
diff --git a/lib/string.c b/lib/string.c
index 3d55ef890106..30a63048d4cc 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -725,7 +725,7 @@ EXPORT_SYMBOL(bcmp);
  * returns the address of the first occurrence of @c, or 1 byte past
  * the area if @c is not found
  */
-void *memscan(void *addr, int c, size_t size)
+void *memscan(const void *addr, int c, size_t size)
 {
 	unsigned char *p = addr;
 
-- 
2.39.1

[PATCH net-next v1 2/2] dns: use memscan() instead of open coded variant

[Andy Shevchenko]

memscan() is a standard API to provide an equivalent to

	memchr(foo, $CHAR, end - foo) ?: end

so use it.

Memory footprint (x86_64):

  Function                                     old     new   delta
  dns_resolver_preparse                       1429    1393     -36
  Total: Before=3229, After=3193, chg -1.11%

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 net/dns_resolver/dns_key.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 01e54b46ae0b..835be6e2dd83 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -134,8 +134,8 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 
 	/* deal with any options embedded in the data */
 	end = data + datalen;
-	opt = memchr(data, '#', datalen);
-	if (!opt) {
+	opt = memscan(data, '#', datalen);
+	if (opt == end) {
 		/* no options: the entire data is the result */
 		kdebug("no options");
 		result_len = datalen;
@@ -150,7 +150,7 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 			const char *eq;
 			char optval[128];
 
-			next_opt = memchr(opt, '#', end - opt) ?: end;
+			next_opt = memscan(opt, '#', end - opt);
 			opt_len = next_opt - opt;
 			if (opt_len <= 0 || opt_len > sizeof(optval)) {
 				pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
@@ -158,16 +158,10 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 				return -EINVAL;
 			}
 
-			eq = memchr(opt, '=', opt_len);
-			if (eq) {
-				opt_nlen = eq - opt;
-				eq++;
-				memcpy(optval, eq, next_opt - eq);
-				optval[next_opt - eq] = '\0';
-			} else {
-				opt_nlen = opt_len;
-				optval[0] = '\0';
-			}
+			eq = memscan(opt, '=', opt_len);
+			opt_nlen = eq - opt;
+			memcpy(optval, eq, next_opt - eq);
+			optval[next_opt - eq] = '\0';
 
 			kdebug("option '%*.*s' val '%s'",
 			       opt_nlen, opt_nlen, opt, optval);
-- 
2.39.1

Re: [PATCH net-next v1 1/2] string: Make memscan() to take const

[Jakub Kicinski]

On Thu, 16 Feb 2023 13:42:33 +0200 Andy Shevchenko wrote:
> Make memscan() to take const so it will be easier replace
> some memchr() cases with it.

Let's do this after the merge window.

Re: [PATCH net-next v1 1/2] string: Make memscan() to take const

[Andy Shevchenko]

On Mon, Feb 20, 2023 at 04:26:53PM -0800, Jakub Kicinski wrote:
> On Thu, 16 Feb 2023 13:42:33 +0200 Andy Shevchenko wrote:
> > Make memscan() to take const so it will be easier replace
> > some memchr() cases with it.
> 
> Let's do this after the merge window.

Sure, it needs to be revised anyway. I just noticed that one corner case might
not work properly.

-- 
With Best Regards,
Andy Shevchenko