chardev: Propagate error from logfile opening

If a chardev has a logfile the file is opened using
qemu_open_old() which does the job, but since @errp is not
propagated into qemu_open_internal() we lose much more accurate
error and just report "Unable to open logfile $errno".  When
using plain files, it's probably okay as nothing complex is
happening behind the curtains. But the problem becomes more
prominent when passing an "/dev/fdset/XXX" path since much more
needs to be done.

The fix is to use qemu_create() which passes @errp further down.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <f34ee80866e6f591bcb98401dee27682f5543fca.1629190206.git.mprivozn@redhat.com>

chardev/char.c

@@ -241,18 +241,15 @@ static void qemu_char_open(Chardev *chr, ChardevBackend *backend,
     ChardevCommon *common = backend ? backend->u.null.data : NULL;
 
     if (common && common->has_logfile) {
-        int flags = O_WRONLY | O_CREAT;
+        int flags = O_WRONLY;
         if (common->has_logappend &&
             common->logappend) {
             flags |= O_APPEND;
         } else {
             flags |= O_TRUNC;
         }
-        chr->logfd = qemu_open_old(common->logfile, flags, 0666);
+        chr->logfd = qemu_create(common->logfile, flags, 0666, errp);
         if (chr->logfd < 0) {
-            error_setg_errno(errp, errno,
-                             "Unable to open logfile %s",
-                             common->logfile);
             return;
         }
     }