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

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2 01/20] cutils: Provide strchrnul
Date: Fri, 1 Jun 2018 09:15:55 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

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 <address@hidden>

+++ 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

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