qemu-sockets: do not test path with access() before unlinking

Using access() is a time-of-check/time-of-use race condition.  It is
okay to use them to provide better error messages, but that is pretty
much it.

This is not one such case; on the other hand, access() *will* skip
unlink() for a non-existent path, so ignore ENOENT return values from
the unlink() system call.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

util/qemu-sockets.c

@@ -751,8 +751,7 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
         qemu_opt_set(opts, "path", un.sun_path, &error_abort);
     }
 
-    if ((access(un.sun_path, F_OK) == 0) &&
-        unlink(un.sun_path) < 0) {
+    if (unlink(un.sun_path) < 0 && errno != ENOENT) {
         error_setg_errno(errp, errno,
                          "Failed to unlink socket %s", un.sun_path);
         goto err;