qemu_strnlen() uses a byte-at-a-time loop with an XXX TODO
comment noting that the host strnlen() could be used instead.

strnlen() is POSIX.1-2008 and is available on all platforms QEMU
supports (guaranteed by qemu/osdep.h).  The host C library
implementation typically uses word-at-a-time or SIMD scanning,
which is significantly faster for long strings.

Replace the loop with a direct call to strnlen().  Add an explicit
cast from size_t to int since qemu_strnlen() returns int while
strnlen() returns size_t; the cast is safe because max_len (the
upper bound on the return value) is already int.

Signed-off-by: Bin Guo <guobin@linux.alibaba.com>
---
 util/cutils.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/util/cutils.c b/util/cutils.c
index 76a9442085..9869d8842d 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -118,17 +118,9 @@ int stristart(const char *str, const char *val, const char **ptr)
     return 1;
 }
 
-/* XXX: use host strnlen if available ? */
 int qemu_strnlen(const char *s, int max_len)
 {
-    int i;
-
-    for(i = 0; i < max_len; i++) {
-        if (s[i] == '\0') {
-            break;
-        }
-    }
-    return i;
+    return (int)strnlen(s, max_len);
 }
 
 char *qemu_strsep(char **input, const char *delim)
-- 
2.50.1 (Apple Git-155)

Hi,

On 29/5/26 04:38, Bin Guo wrote:
> qemu_strnlen() uses a byte-at-a-time loop with an XXX TODO
> comment noting that the host strnlen() could be used instead.
> 
> strnlen() is POSIX.1-2008 and is available on all platforms QEMU
> supports (guaranteed by qemu/osdep.h).

If so, there are only 3 uses in the code base. Maybe drop
qemu_strnlen() altogether, using size_t in the callers?

>  The host C library
> implementation typically uses word-at-a-time or SIMD scanning,
> which is significantly faster for long strings.
> 
> Replace the loop with a direct call to strnlen().  Add an explicit
> cast from size_t to int since qemu_strnlen() returns int while
> strnlen() returns size_t; the cast is safe because max_len (the
> upper bound on the return value) is already int.
> 
> Signed-off-by: Bin Guo <guobin@linux.alibaba.com>
> ---
>   util/cutils.c | 10 +---------
>   1 file changed, 1 insertion(+), 9 deletions(-)

On Fri, 29 May 2026 08:02:41 +0200, Philippe Mathieu-Daude wrote:
> there are only 3 uses in the code base. Maybe drop qemu_strnlen()
> altogether, using size_t in the callers?

Good suggestion. I've sent a v2 that drops qemu_strnlen() entirely and
switches all callers to strnlen() directly. I also aligned bsd-user/uaccess.c
to use size_t for max_len/len, matching linux-user/uaccess.c.

New patch:
https://lore.kernel.org/qemu-devel/20260529072803.99475-1-guobin@linux.alibaba.com/

Thanks,
Bin Guo