Re: [PATCH v5 net-next 11/16] net: propagate errors from dev_get_stats

[Vladimir Oltean <olteanv@gmail.com>]

On Fri, Jan 08, 2021 at 06:31:54PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> 
> dev_get_stats can now return error codes. Take the remaining call sites
> where those errors can be propagated, which are all trivial, and convert
> them to look at that error code and stop processing.
> 
> The effects of simulating a kernel error (returning -ENOMEM) upon
> existing programs or kernel interfaces:
> 
> - cat /proc/net/dev prints up until the interface that failed, and there
>   it returns:
> cat: read error: Cannot allocate memory
> 
> - ifstat simply returns this and prints nothing:
> Error: Buffer too small for object.
> Dump terminated
> 
> - ip -s -s link show behaves the same as ifstat.

Note that at first I did not understand why ifstat and "ip -s -s link
show" return this message. But in the meantime I figured that it was due
to rtnetlink still returning -EMSGSIZE. That is fixed in this patch
series, but I forgot to update the commit message to reflect it. The
current output from these two commands is:

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

> 
> - ifconfig prints only the info for the interfaces whose statistics did
>   not fail.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> Changes in v5:
> - Actually propagate errors from bonding and net_failover from within
>   this patch.
> - Properly propagating the dev_get_stats() error code from
>   rtnl_fill_stats now, and not -EMSGSIZE.
> 
> Changes in v4:
> Patch is new (Eric's suggestion).