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

On Tue, 2021-01-12 at 01:15 +0200, Vladimir Oltean wrote:

On Mon, Jan 11, 2021 at 02:54:50PM -0800, Saeed Mahameed wrote:

quoted

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

quoted

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 ?

So you're worried that user space apps won't handle an error code
when
reading from a file, but you're not worried that they'll start
scraping
junk from procfs when we print this?

both are equivalently concerning.
to avoid any user crashes, we can just toss failed netdevs out from the
output.

cat /proc/net/dev
Inter-
|   Receive                                                |  Transmi
t
 face |bytes    packets errs drop fifo frame compressed
multicast|bytes    packets errs drop fifo colls carrier compressed
    lo:       0       0    0    0    0     0          0         0    
    0       0    0    0    0     0       0          0
 bond0: Cannot allocate memory
 
sit0:       0       0    0    0    0     0          0         0      
  0       0    0    0    0     0       0          0