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

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Date:   Fri, 8 Jan 2021 19:22:29 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <edumazet@...gle.com>,
        George McCollister <george.mccollister@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Arnd Bergmann <arnd@...db.de>, Taehee Yoo <ap420073@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, Florian Westphal <fw@...len.de>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Pravin B Shelar <pshelar@....org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH v5 net-next 11/16] net: propagate errors from
 dev_get_stats

On Fri, Jan 08, 2021 at 06:31:54PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....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@....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).