K 10
svn:author
V 7
glebius
K 8
svn:date
V 27
2015-01-16T11:45:54.030354Z
K 7
svn:log
V 1492
Make API around if_mtu, if_capabilities, if_capenable and if_hwassist
more strict.  Disallow direct access to these fields at all.

o if_mtu
  - Stack guarantees that any MTU change attempt is reported via SIOCSIFMTU,
    so drivers can store it in softc and don't need go to ifnet layer.
  - Stack does the equal MTU check, drivers don't need to copy & paste it.
  - If driver doesn't report error, then stack updates MTU.
o if_capabilities
  - Drivers should init them in ifat_capabilities at if_attach(), and are
    not allowed to modify later. Stack neither.
o if_capenable
  - Stack guarantees that any capenable change is reported via SIOCSIFCAP.
    Stack supplies current capabilities (in case if driver doesn't store them)
    in ifr_curcap, and requested capabilities in ifr_reqcap.
  - Stack does the equal check, as well as that requested capenable are subset
    of interface capabilities. Drivers don't need to cut-n-paste that.
  - Stack enforces IFCAP_VLAN_HWTAGGING in case of IFCAP_VLAN_HWTSO.
  - Drivers may alter ifr_reqcap, as in some edge cases they could be
    actually not capable of running capabilities announced at if_attach.
  - Drivers must either return error or, return 0 and in the latter case must
    initialize ifr_hwassist value in the ifreq.
o There are some edge cases when a driver may want to change its capenable
  as result of MTU change. Or vice versa? In this case, the driver should call
  if_drvioctl() upon itself.

Sponsored by:	Nginx, Inc.

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