netdev - Re: [PATCH iproute2] iplink: work around rtattr length limits for IFLA_VFINFO

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Message-ID: <20210118183015.aelwbgfzrsctjek7@lion.mk-sys.cz>
Date:   Mon, 18 Jan 2021 19:30:15 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Edwin Peer <edwin.peer@...adcom.com>
Cc:     David Ahern <dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Andrew Gospodarek <andrew.gospodarek@...adcom.com>,
        Michael Chan <michael.chan@...adcom.com>
Subject: Re: [PATCH iproute2] iplink: work around rtattr length limits for
 IFLA_VFINFO_LIST

On Mon, Jan 18, 2021 at 10:20:35AM -0800, Edwin Peer wrote:
> On Mon, Jan 18, 2021 at 9:49 AM David Ahern <dsahern@...il.com> wrote:
> 
> > Different bug, different solution required. The networking stack hits
> > these kind of scalability problems from time to time with original
> > uapis, so workarounds are needed. One example is rtmsg which only allows
> > 255 routing tables, so RTA_TABLE attribute was added as a u32. Once a
> > solution is found for the VF problem, iproute2 can be enhanced to
> > accommodate.
> 
> The problem is even worse, because user space already depends on the
> broken behavior. Erroring out will cause the whole ip link show
> command to fail, which works today. Even though the VF list is bust,
> the rest of the netdevs are still dumped correctly. A hard fail would
> break those too.

We could cut the list just before overflowing and inform userspace that
the list is incomplete. Not perfect but there is no perfect solution
which would not require userspace changes to work properly for devices
with "too many" VFs.

Michal