Re: [PATCH V2] rtnetlink: Fix problem with buffer allocation

[David Miller <davem@xxxxxxxxxxxxx>]

From: Greg Rose <gregory.v.rose@xxxxxxxxx>
Date: Tue, 21 Feb 2012 13:51:28 -0800

> Implement a new netlink attribute type IFLA_EXT_MASK.  The mask
> is a 32 bit value that can be used to indicate to the kernel that
> certain extended ifinfo values are requested by the user application.
> At this time the only mask value defined is RTEXT_FILTER_VF to
> indicate that the user wants the ifinfo dump to send information
> about the VFs belonging to the interface.
> 
> This patch fixes a bug in which certain applications do not have
> large enough buffers to accommodate the extra information returned
> by the kernel with large numbers of SR-IOV virtual functions.
> Those applications will not send the new netlink attribute with
> the interface info dump request netlink messages so they will
> not get unexpectedly large request buffers returned by the kernel.
> 
> Modifies the rtnl_calcit function to traverse the list of net
> devices and compute the minimum buffer size that can hold the
> info dumps of all matching devices based upon the filter passed
> in via the new netlink attribute filter mask.  If no filter
> mask is sent then the buffer allocation defaults to NLMSG_GOODSIZE.
> 
> With this change it is possible to add yet to be defined netlink
> attributes to the dump request which should make it fairly extensible
> in the future.
> 
> CC: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Greg Rose <gregory.v.rose@xxxxxxxxx>

Applied, with the minor change suggested by Eric in that we can
use the non-RCU list traversal in the calcit function because
we hold the RTNL always when this is invoked.

Thanks!
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