From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schiller Subject: Re: [PATCH net-next RFC v4] net: hdlc_x25: Queue outgoing LAPB frames Date: Mon, 22 Feb 2021 08:14:07 +0100 Message-ID: <906d8114f1965965749f1890680f2547@dev.tdt.de> References: <20210216201813.60394-1-xie.he.0141@gmail.com> <20210219103948.6644e61f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Xie He Cc: Jakub Kicinski , Leon Romanovsky , "David S. Miller" , Linux X25 , Linux Kernel Network Developers , LKML , Krzysztof Halasa , Jonathan Corbet , linux-doc@vger.kernel.org On 2021-02-19 21:28, Xie He wrote: > On Fri, Feb 19, 2021 at 10:39 AM Jakub Kicinski > wrote: >> >> Not entirely sure what the argument is about but adding constants >> would >> certainly help. > > Leon wants me to replace this: > > dev->needed_headroom = 3 - 1; > > with this: > > /* 2 is the result of 3 - 1 */ > dev->needed_headroom = 2; > > But I don't feel his way is better than my way. > >> More fundamentally IDK if we can make such a fundamental change here. >> When users upgrade from older kernel are all their scripts going to >> work the same? Won't they have to bring the new netdev up? > > Yes, this patch will break backward compatibility. Users with old > scripts will find them no longer working. > > However, it's hard for me to find a better way to solve the problem > described in the commit message. > > So I sent this as an RFC to see what people think about this. (Martin > Schiller seems to be OK with this.) Well, I said I would like to test it. I'm not really happy with this change because it breaks compatibility. We then suddenly have 2 interfaces; the X.25 routings are to be set via the "new" hdlc_x25 interfaces instead of the hdlc interfaces. I currently just don't have a nicer solution to fix this queueing problem either. On the other hand, since the many years we have been using the current state, I have never noticed any problems with discarded frames. So it might be more a theoretical problem than a practical one. > > I think users who don't use scripts can adapt quickly and users who > use scripts can also trivally fix their scripts. > > Actually many existing commits in the kernel also (more or less) cause > some user-visible changes. But I admit this patch is a really big > change.