Re: [PATCHv2] properly handle point-to-point interfaces in getifaddrs()

[Timo Teras <timo.teras@iki.fi>]

On Thu, 19 Nov 2015 21:43:10 +0100
Jo-Philipp Wich <jow@openwrt.org> wrote:

> With point-to-point interfaces, the IFA_ADDRESS netlink attribute
> contains the peer address while an extra attribute IFA_LOCAL carries
> the actual local interface address.
> 
> Both the glibc and uclibc implementations of getifaddrs() handle this
> case by moving the ifa_addr contents to the broadcast/remote address
> union and overwriting ifa_addr upon receipt of an IFA_LOCAL attribute.
> 
> This patch adds the same special treatment logic of IFA_LOCAL to
> musl's implementation of getifaddrs() in order to align its behaviour
> with that of uclibc and musl.
> 
> Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
> ---
> Changelog v2:
>  * Handle IFA_LOCAL, IFA_ADDRESS in arbritary order
>  * Remove misleading comment for IFA_BROADCAST, no such attribute on
> ptp links ---
>  src/network/getifaddrs.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)

I wrote the code before looking into how ptp links are reported, and
just assumed it'd be somehow consistent. But IFA_ADDRESS indeed is
the peer for ptp links. How nicely inconsistent from kernel side ;)

Seems iproute2 basically does:
 1. If IFA_LOCAL not set, copy IFA_ADDRESS to it
 2. If IFA_ADDRESS is not set, copy IFA_LOCAL to it
 3. Print IFA_LOCAL as local address
 4. Print IFA_ADDRESS as peer address if it's not equal to IFA_LOCAL

So this looks right to me.

Acked-by: Timo Teräs <timo.teras@iki.fi>