• Randall Stewart's avatar
    tcp: Congestion control cleanup. · b8d60729
    Randall Stewart authored
    NOTE: HEADS UP read the note below if your kernel config is not including GENERIC!!
    This patch does a bit of cleanup on TCP congestion control modules. There were some rather
    interesting surprises that one could get i.e. where you use a socket option to change
    from one CC (say cc_cubic) to another CC (say cc_vegas) and you could in theory get
    a memory failure and end up on cc_newreno. This is not what one would expect. The
    new code fixes this by requiring a cc_data_sz() function so we can malloc with M_WAITOK
    and pass in to the init function preallocated memory. The CC init is expected in this
    case *not* to fail but if it does and a module does break the
    "no fail with memory given" contract we do fall back to the CC that was in place at the time.
    This also fixes up a set of common newreno utilities that can be shared amongst other
    CC modules instead of the other CC modules reaching into newreno and executing
    what they think is a "common and understood" function. Lets put these functions in
    cc.c and that way we have a common place that is easily findable by future developers or
    bug fixers. This also allows newreno to evolve and grow support for its features i.e. ABE
    and HYSTART++ without having to dance through hoops for other CC modules, instead
    both newreno and the other modules just call into the common functions if they desire
    that behavior or roll there own if that makes more sense.
    Note: This commit changes the kernel configuration!! If you are not using GENERIC in
    some form you must add a CC module option (one of CC_NEWRENO, CC_VEGAS, CC_CUBIC,
    CC_CDG, CC_CHD, CC_DCTCP, CC_HTCP, CC_HD). You can have more than one defined
    as well if you desire. Note that if you create a kernel configuration that does not
    define a congestion control module and includes INET or INET6 the kernel compile will
    break. Also you need to define a default, generic adds 'options CC_DEFAULT=\"newreno\"
    but you can specify any string that represents the name of the CC module (same names
    that show up in the CC module list under net.inet.tcp.cc). If you fail to add the
    options CC_DEFAULT in your kernel configuration the kernel build will also break.
    Reviewed by: Michael Tuexen
    Sponsored by: Netflix Inc.
    Differential Revision: https://reviews.freebsd.org/D32693