• Eric Dumazet's avatar
    ip: Report qdisc packet drops · 6ce9e7b5
    Eric Dumazet authored
    Christoph Lameter pointed out that packet drops at qdisc level where not
    accounted in SNMP counters. Only if application sets IP_RECVERR, drops
    are reported to user (-ENOBUFS errors) and SNMP counters updated.
    
    IP_RECVERR is used to enable extended reliable error message passing,
    but these are not needed to update system wide SNMP stats.
    
    This patch changes things a bit to allow SNMP counters to be updated,
    regardless of IP_RECVERR being set or not on the socket.
    
    Example after an UDP tx flood
    # netstat -s 
    ...
    IP:
        1487048 outgoing packets dropped
    ...
    Udp:
    ...
        SndbufErrors: 1487048
    
    
    send() syscalls, do however still return an OK status, to not
    break applications.
    
    Note : send() manual page explicitly says for -ENOBUFS error :
    
     "The output queue for a network interface was full.
      This generally indicates that the interface has stopped sending,
      but may be caused by transient congestion.
      (Normally, this does not occur in Linux. Packets are just silently
      dropped when a device queue overflows.) "
    
    This is not true for IP_RECVERR enabled sockets : a send() syscall
    that hit a qdisc drop returns an ENOBUFS error.
    
    Many thanks to Christoph, David, and last but not least, Alexey !
    Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    6ce9e7b5
udp.c 32.2 KB