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SubjectRe: 2.2.13 ISDN funnies

Karsten Keil <kkeil@suse.de> writes:

>Again, no headroom isn't a error, only a bad thing, which cost a extra
>copy of the frame to have enought place for the header.

I'd really consider this to be an error. The net device posts its
requirement for the link layer's skb headspace in the dev->hard_header_len
field. If the network layer passed an skb to the device (dev->hard_header())
with insufficient headroom < dev->hard_header, this would be a bug in the
network layer. (BTW, the network layers already reallocates headroom if
necessary. Thus, it should never be necessary inside the driver).

If dev->hard_header_len were set too small compared to the real
requirements of the driver, this would be a bug in the driver. There is
a possible bug which could cause this in theory, but this could only be
triggered if two different HL drivers were used but the one with the larger
headspace requirements was insmod'ed after the network interface was
registered. No reasonnable setup scripts would do so anyway and the error
reports received until now only use one driver insmod'ed before
the interface is registered. Thus, this potential driver bug is certaninly
not responsible for the error reports.

I really doubt that the problem is caused inside the linux network layers.
Otherwise, the same bug would trigger skb_uflow panics with any
net_device driver.

Henner

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