Date: Thu, 19 Dec 2013 19:16:06 +0400 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Adrian Chadd <adrian@freebsd.org> Cc: Jack F Vogel <jfv@freebsd.org>, Michael Tuexen <Michael.Tuexen@lurchi.franken.de>, Ryan Stone <rysto32@gmail.com>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: Removing queue length check in ip_output (was Re: buf_ring in HEAD is racy) Message-ID: <20131219151606.GB71033@FreeBSD.org> In-Reply-To: <CAJ-VmomyPq_2K-MFhb7vt6MM7RBbmn7yaTzUXb7%2BN7TbW1RmHQ@mail.gmail.com> References: <CAJ-VmomyPq_2K-MFhb7vt6MM7RBbmn7yaTzUXb7%2BN7TbW1RmHQ@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Dec 18, 2013 at 01:04:43PM -0800, Adrian Chadd wrote: A> How about we can this check in ip_output(): A> A> /* A> * Verify that we have any chance at all of being able to queue the A> * packet or packet fragments, unless ALTQ is enabled on the given A> * interface in which case packetdrop should be done by queueing. A> */ A> n = ip_len / mtu + 1; /* how many fragments ? */ A> if ( A> #ifdef ALTQ A> (!ALTQ_IS_ENABLED(&ifp->if_snd)) && A> #endif /* ALTQ */ A> (ifp->if_snd.ifq_len + n) >= ifp->if_snd.ifq_maxlen ) { A> error = ENOBUFS; A> IPSTAT_INC(ips_odropped); A> ifp->if_snd.ifq_drops += n; A> goto bad; A> } A> A> .. it's totally bogus in an if_transmit / SMP world. There's no A> locking and there's no guarantee that there will be headroom in the A> queue between this point and the later call to the if_output() method. My vote is to remove this. But better leave a comment that we need an API to send a bunch of packets (or fail them all) via an interface. -- Totus tuus, Glebius.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20131219151606.GB71033>