netdev - Re: build_skb() and data corruption

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Message-ID: <CACmBeS1gTfdjwiCkHMViOnF6G2zjy3HSMm3NVq8Jiq5F22ynJA@mail.gmail.com>
Date:	Tue, 14 Jan 2014 16:24:06 +0100
From:	Jonas Jensen <jonas.jensen@...il.com>
To:	netdev <netdev@...r.kernel.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	alexander.h.duyck@...el.com, Arnd Bergmann <arnd@...db.de>,
	Florian Fainelli <florian@...nwrt.org>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: build_skb() and data corruption

Thanks for the replies, you led me to a new solution,

I now think build_skb() is not the right choice, my motivation for
using it in the first place, that I thought it meant getting away with
not copying memory.

build_skb() is replaced by netdev_alloc_skb_ip_align() and memcpy()
(derived from drivers/net/ethernet/realtek/r8169.c).

Read errors are gone, even without syncing DMA. Is it a good idea to
do it anyway, i.e. leave calls to dma_sync_single_* in?

Also, without build_skb(), kmalloc memory can be used (frag_size > 0),
memory is used more efficiently, at least half of a page times 64
previously wasted.

New code here:
https://bitbucket.org/Kasreyn/linux-next/src/92f5aeb3b58f8d8dffd9178b6b5ff46217156caa/drivers/net/ethernet/moxa/moxart_ether.c#cl-424

Thanks,
Jonas
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