netdev - Re: tun always return NETDEV_TX

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Tue, 13 Aug 2013 10:33:31 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Yannick Koehler <yannick@...hler.name>
Cc:	netdev@...r.kernel.org
Subject: Re: tun always return NETDEV_TX_OK, why?

On Tue, 13 Aug 2013 10:39:02 -0400
Yannick Koehler <yannick@...hler.name> wrote:

> Hello,
> 
>   I hit a problem recently with the tun interface, it looks like when
> this interface reach its txqueuelen it will then drop the packet and
> return NETDEV_TX_OK unconditionally.
> 
>  That, from my little understanding of the netdev framework, appears
> to be wrong and will simply eat up any pending buffer and discard them
> until the queue frees itself.  That seems to be against the flow
> control design in the tx queue system of the kernel.
> 
>   So, is this a bug or a misunderstanding?  Would it be ok for tun to
> return NETDEV_TX_BUSY when the txqueuelen is reach and call
> netif_stop_queue() so that the layer above stop sending frame to this
> interface until it can cope it's current queue content?
> 

NETDEV_TX_BUSY won't work well for this because it basically
causes kernel to spin waiting for the transmit queue.
A better way is to figure out how to do proper flow control
with start/stop queue.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html