Re: [PATCH v6 net-next 11/15] net: catch errors from dev_get_stats

On Sat, 2021-01-09 at 19:26 +0200, Vladimir Oltean wrote:

From: Vladimir Oltean <vladimir.oltean@nxp.com>

dev_get_stats can now return error codes. Convert all remaining call
sites to look at that error code and stop processing.

The effects of simulating a kernel error (returning -ENOMEM) upon
existing programs or kernel interfaces:

- ifconfig and "cat /proc/net/dev" print up until the interface that
  failed, and there they return:
cat: read error: Cannot allocate memory

- ifstat and "ip -s -s link show":
RTNETLINK answers: Cannot allocate memory
Dump terminated

Some call sites are coming from a context that returns void (ethtool
stats, workqueue context). So since we can't report to the upper
layer,
do the next best thing: print an error to the console.

another concern, one buggy netdev driver in a system will cause
unnecessary global failures when reading stats via netlink/procfs for
all the netdev in a netns, when other drivers will be happy to report.

can't we just show a message in that driver's stats line about the
occurred err ? and show the normal stats line of all others ?

This patch wraps up the conversion of existing dev_get_stats callers,
so
we can add the __must_check attribute now to ensure that future
callers
keep doing this too.