Re: [Qemu-devel] [PATCH v2 01/20] cutils: Provide strchrnul

[Eric Blake <eblake@redhat.com>]

On 05/31/2018 08:25 PM, Keno Fischer wrote:
> strchrnul is a GNU extension and thus unavailable on a number of targets.
> In the review for a commit removing strchrnul from 9p, I was asked to
> create a qemu_strchrnul helper to factor out this functionality.
> Do so, and use it in a number of other places in the code base that inlined
> the replacement pattern in a place where strchrnul could be used.
> 
> Signed-off-by: Keno Fischer <keno@juliacomputing.com>
> ---
> 

> +++ b/util/cutils.c
> @@ -545,6 +545,19 @@ int qemu_strtou64(const char *nptr, const char **endptr, int base,
>   }
>   
>   /**
> + * Searches for the first occurrence of 'c' in 's', and returns a pointer
> + * to the trailing null byte if none was found.
> + */
> +const char *qemu_strchrnul(const char *s, int c)
> +{
> +    const char *e = strchr(s, c);
> +    if (!e) {
> +        e = s + strlen(s);
> +    }
> +    return e;
> +}

This is twice as slow on glibc systems when the pointer to NUL is 
returned (because it has to traverse the string twice); it's better to 
have a configure check for whether strchrnul exists, and if so, use that 
directly.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org