git: carp: Lock MPSAFE, step 10 of 11

[Sepherosa Ziehau]

commit bb05f5cdc30aad020abec4b2b54773a045f4ac27
Author: Sepherosa Ziehau <sephe at dragonflybsd.org>
Date:   Mon Apr 9 21:06:57 2012 +0800

    carp: Lock MPSAFE, step 10 of 11
    
    Make carp_softc.sc_carpdev and ifnet.if_carp accessing and updating
    lockless MPSAFE.
    
    carp_softc.sc_carpdev:
    - Reader of the sc_carpdev will cache the value in temporary variable
      and use the cached value instead of always accessing sc_carpdev,
      which may be inconsistent due to change of sc_carpdev.
    
    ifnet.if_carp
    - if_carp is a pointer to the carp_softc container list, while the list
      only contains pointer to carp_softc
    - Reader of if_carp will cache the value in temporary variable and use
      the cached value instead of always accessing if_carp, which may be
      inconsistent due to if_carp updating.
    - Updating of the if_carp is done in the following way:
        ocif = ifp->if_carp;
        ncif = cif_copy(ocif);
        cif_modify(ncif);
        ifp->if_carp = ncif;
        netmsg_service_sync();
        /* when we reach here all users of old if_carp (ocif) are done */
        cif_free(ocif)

Summary of changes:
 sys/net/if_ethersubr.c |   27 +++--
 sys/netinet/ip_carp.c  |  279 +++++++++++++++++++++++++++++++++++-------------
 sys/netinet/ip_carp.h  |    1 -
 3 files changed, 222 insertions(+), 85 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/bb05f5cdc30aad020abec4b2b54773a045f4ac27


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