musl: hostname-util: introduce LINUX_HOST_NAME_MAX

glibc defines HOST_NAME_MAX as 64 and our code rely on that, but musl
defines the constant as 255. Let's provide our own definition for the
maximum length.

src/basic/hostname-util.c

@@ -94,8 +94,8 @@ bool hostname_is_valid(const char *s, ValidHostnameFlags flags) {
         if (hyphen)
                 return false;
 
-        if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on Linux, but DNS allows domain names up to
-                                  * 255 characters */
+        /* Note that host name max is 64 on Linux, but DNS allows domain names up to 255 characters. */
+        if (p - s > (ssize_t) LINUX_HOST_NAME_MAX)
                 return false;
 
         return true;
@@ -107,7 +107,7 @@ char* hostname_cleanup(char *s) {
 
         assert(s);
 
-        for (p = s, d = s, dot = hyphen = true; *p && d - s < HOST_NAME_MAX; p++)
+        for (p = s, d = s, dot = hyphen = true; *p && d - s < (ssize_t) LINUX_HOST_NAME_MAX; p++)
                 if (*p == '.') {
                         if (dot || hyphen)
                                 continue;

src/basic/hostname-util.h

@@ -4,6 +4,9 @@
 #include "basic-forward.h"
 #include "strv.h"
 
+/* HOST_NAME_MAX should be 64 on linux, but musl uses the one by POSIX (255). */
+#define LINUX_HOST_NAME_MAX CONST_MIN((size_t) HOST_NAME_MAX, (size_t) 64)
+
 char* get_default_hostname_raw(void);
 
 bool valid_ldh_char(char c) _const_;