1. 16 6月, 2017 1 次提交
    • J
      networking: make skb_pull & friends return void pointers · af72868b
      Johannes Berg 提交于
      It seems like a historic accident that these return unsigned char *,
      and in many places that means casts are required, more often than not.
      
      Make these functions return void * and remove all the casts across
      the tree, adding a (u8 *) cast only where the unsigned char pointer
      was used directly, all done with the following spatch:
      
          @@
          expression SKB, LEN;
          typedef u8;
          identifier fn = {
                  skb_pull,
                  __skb_pull,
                  skb_pull_inline,
                  __pskb_pull_tail,
                  __pskb_pull,
                  pskb_pull
          };
          @@
          - *(fn(SKB, LEN))
          + *(u8 *)fn(SKB, LEN)
      
          @@
          expression E, SKB, LEN;
          identifier fn = {
                  skb_pull,
                  __skb_pull,
                  skb_pull_inline,
                  __pskb_pull_tail,
                  __pskb_pull,
                  pskb_pull
          };
          type T;
          @@
          - E = ((T *)(fn(SKB, LEN)))
          + E = fn(SKB, LEN)
      Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      af72868b
  2. 08 6月, 2017 1 次提交
    • D
      net: Fix inconsistent teardown and release of private netdev state. · cf124db5
      David S. Miller 提交于
      Network devices can allocate reasources and private memory using
      netdev_ops->ndo_init().  However, the release of these resources
      can occur in one of two different places.
      
      Either netdev_ops->ndo_uninit() or netdev->destructor().
      
      The decision of which operation frees the resources depends upon
      whether it is necessary for all netdev refs to be released before it
      is safe to perform the freeing.
      
      netdev_ops->ndo_uninit() presumably can occur right after the
      NETDEV_UNREGISTER notifier completes and the unicast and multicast
      address lists are flushed.
      
      netdev->destructor(), on the other hand, does not run until the
      netdev references all go away.
      
      Further complicating the situation is that netdev->destructor()
      almost universally does also a free_netdev().
      
      This creates a problem for the logic in register_netdevice().
      Because all callers of register_netdevice() manage the freeing
      of the netdev, and invoke free_netdev(dev) if register_netdevice()
      fails.
      
      If netdev_ops->ndo_init() succeeds, but something else fails inside
      of register_netdevice(), it does call ndo_ops->ndo_uninit().  But
      it is not able to invoke netdev->destructor().
      
      This is because netdev->destructor() will do a free_netdev() and
      then the caller of register_netdevice() will do the same.
      
      However, this means that the resources that would normally be released
      by netdev->destructor() will not be.
      
      Over the years drivers have added local hacks to deal with this, by
      invoking their destructor parts by hand when register_netdevice()
      fails.
      
      Many drivers do not try to deal with this, and instead we have leaks.
      
      Let's close this hole by formalizing the distinction between what
      private things need to be freed up by netdev->destructor() and whether
      the driver needs unregister_netdevice() to perform the free_netdev().
      
      netdev->priv_destructor() performs all actions to free up the private
      resources that used to be freed by netdev->destructor(), except for
      free_netdev().
      
      netdev->needs_free_netdev is a boolean that indicates whether
      free_netdev() should be done at the end of unregister_netdevice().
      
      Now, register_netdevice() can sanely release all resources after
      ndo_ops->ndo_init() succeeds, by invoking both ndo_ops->ndo_uninit()
      and netdev->priv_destructor().
      
      And at the end of unregister_netdevice(), we invoke
      netdev->priv_destructor() and optionally call free_netdev().
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      cf124db5
  3. 22 4月, 2017 1 次提交
    • N
      ip6mr: fix notification device destruction · 723b929c
      Nikolay Aleksandrov 提交于
      Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
      because we call unregister_netdevice_many for a device that is already
      being destroyed. In IPv4's ipmr that has been resolved by two commits
      long time ago by introducing the "notify" parameter to the delete
      function and avoiding the unregister when called from a notifier, so
      let's do the same for ip6mr.
      
      The trace from Andrey:
      ------------[ cut here ]------------
      kernel BUG at net/core/dev.c:6813!
      invalid opcode: 0000 [#1] SMP KASAN
      Modules linked in:
      CPU: 1 PID: 1165 Comm: kworker/u4:3 Not tainted 4.11.0-rc7+ #251
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
      01/01/2011
      Workqueue: netns cleanup_net
      task: ffff880069208000 task.stack: ffff8800692d8000
      RIP: 0010:rollback_registered_many+0x348/0xeb0 net/core/dev.c:6813
      RSP: 0018:ffff8800692de7f0 EFLAGS: 00010297
      RAX: ffff880069208000 RBX: 0000000000000002 RCX: 0000000000000001
      RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88006af90569
      RBP: ffff8800692de9f0 R08: ffff8800692dec60 R09: 0000000000000000
      R10: 0000000000000006 R11: 0000000000000000 R12: ffff88006af90070
      R13: ffff8800692debf0 R14: dffffc0000000000 R15: ffff88006af90000
      FS:  0000000000000000(0000) GS:ffff88006cb00000(0000)
      knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007fe7e897d870 CR3: 00000000657e7000 CR4: 00000000000006e0
      Call Trace:
       unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
       unregister_netdevice_many+0xc8/0x120 net/core/dev.c:7880
       ip6mr_device_event+0x362/0x3f0 net/ipv6/ip6mr.c:1346
       notifier_call_chain+0x145/0x2f0 kernel/notifier.c:93
       __raw_notifier_call_chain kernel/notifier.c:394
       raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
       call_netdevice_notifiers_info+0x51/0x90 net/core/dev.c:1647
       call_netdevice_notifiers net/core/dev.c:1663
       rollback_registered_many+0x919/0xeb0 net/core/dev.c:6841
       unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
       unregister_netdevice_many net/core/dev.c:7880
       default_device_exit_batch+0x4fa/0x640 net/core/dev.c:8333
       ops_exit_list.isra.4+0x100/0x150 net/core/net_namespace.c:144
       cleanup_net+0x5a8/0xb40 net/core/net_namespace.c:463
       process_one_work+0xc04/0x1c10 kernel/workqueue.c:2097
       worker_thread+0x223/0x19c0 kernel/workqueue.c:2231
       kthread+0x35e/0x430 kernel/kthread.c:231
       ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
      Code: 3c 32 00 0f 85 70 0b 00 00 48 b8 00 02 00 00 00 00 ad de 49 89
      47 78 e9 93 fe ff ff 49 8d 57 70 49 8d 5f 78 eb 9e e8 88 7a 14 fe <0f>
      0b 48 8b 9d 28 fe ff ff e8 7a 7a 14 fe 48 b8 00 00 00 00 00
      RIP: rollback_registered_many+0x348/0xeb0 RSP: ffff8800692de7f0
      ---[ end trace e0b29c57e9b3292c ]---
      Reported-by: NAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
      Tested-by: NAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      723b929c
  4. 29 3月, 2017 1 次提交
  5. 27 2月, 2017 1 次提交
  6. 19 1月, 2017 1 次提交
  7. 03 1月, 2017 1 次提交
  8. 25 12月, 2016 1 次提交
  9. 01 11月, 2016 1 次提交
  10. 26 9月, 2016 1 次提交
    • N
      ipmr, ip6mr: fix scheduling while atomic and a deadlock with ipmr_get_route · 2cf75070
      Nikolay Aleksandrov 提交于
      Since the commit below the ipmr/ip6mr rtnl_unicast() code uses the portid
      instead of the previous dst_pid which was copied from in_skb's portid.
      Since the skb is new the portid is 0 at that point so the packets are sent
      to the kernel and we get scheduling while atomic or a deadlock (depending
      on where it happens) by trying to acquire rtnl two times.
      Also since this is RTM_GETROUTE, it can be triggered by a normal user.
      
      Here's the sleeping while atomic trace:
      [ 7858.212557] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620
      [ 7858.212748] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
      [ 7858.212881] 2 locks held by swapper/0/0:
      [ 7858.213013]  #0:  (((&mrt->ipmr_expire_timer))){+.-...}, at: [<ffffffff810fbbf5>] call_timer_fn+0x5/0x350
      [ 7858.213422]  #1:  (mfc_unres_lock){+.....}, at: [<ffffffff8161e005>] ipmr_expire_process+0x25/0x130
      [ 7858.213807] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.8.0-rc7+ #179
      [ 7858.213934] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
      [ 7858.214108]  0000000000000000 ffff88005b403c50 ffffffff813a7804 0000000000000000
      [ 7858.214412]  ffffffff81a1338e ffff88005b403c78 ffffffff810a4a72 ffffffff81a1338e
      [ 7858.214716]  000000000000026c 0000000000000000 ffff88005b403ca8 ffffffff810a4b9f
      [ 7858.215251] Call Trace:
      [ 7858.215412]  <IRQ>  [<ffffffff813a7804>] dump_stack+0x85/0xc1
      [ 7858.215662]  [<ffffffff810a4a72>] ___might_sleep+0x192/0x250
      [ 7858.215868]  [<ffffffff810a4b9f>] __might_sleep+0x6f/0x100
      [ 7858.216072]  [<ffffffff8165bea3>] mutex_lock_nested+0x33/0x4d0
      [ 7858.216279]  [<ffffffff815a7a5f>] ? netlink_lookup+0x25f/0x460
      [ 7858.216487]  [<ffffffff8157474b>] rtnetlink_rcv+0x1b/0x40
      [ 7858.216687]  [<ffffffff815a9a0c>] netlink_unicast+0x19c/0x260
      [ 7858.216900]  [<ffffffff81573c70>] rtnl_unicast+0x20/0x30
      [ 7858.217128]  [<ffffffff8161cd39>] ipmr_destroy_unres+0xa9/0xf0
      [ 7858.217351]  [<ffffffff8161e06f>] ipmr_expire_process+0x8f/0x130
      [ 7858.217581]  [<ffffffff8161dfe0>] ? ipmr_net_init+0x180/0x180
      [ 7858.217785]  [<ffffffff8161dfe0>] ? ipmr_net_init+0x180/0x180
      [ 7858.217990]  [<ffffffff810fbc95>] call_timer_fn+0xa5/0x350
      [ 7858.218192]  [<ffffffff810fbbf5>] ? call_timer_fn+0x5/0x350
      [ 7858.218415]  [<ffffffff8161dfe0>] ? ipmr_net_init+0x180/0x180
      [ 7858.218656]  [<ffffffff810fde10>] run_timer_softirq+0x260/0x640
      [ 7858.218865]  [<ffffffff8166379b>] ? __do_softirq+0xbb/0x54f
      [ 7858.219068]  [<ffffffff816637c8>] __do_softirq+0xe8/0x54f
      [ 7858.219269]  [<ffffffff8107a948>] irq_exit+0xb8/0xc0
      [ 7858.219463]  [<ffffffff81663452>] smp_apic_timer_interrupt+0x42/0x50
      [ 7858.219678]  [<ffffffff816625bc>] apic_timer_interrupt+0x8c/0xa0
      [ 7858.219897]  <EOI>  [<ffffffff81055f16>] ? native_safe_halt+0x6/0x10
      [ 7858.220165]  [<ffffffff810d64dd>] ? trace_hardirqs_on+0xd/0x10
      [ 7858.220373]  [<ffffffff810298e3>] default_idle+0x23/0x190
      [ 7858.220574]  [<ffffffff8102a20f>] arch_cpu_idle+0xf/0x20
      [ 7858.220790]  [<ffffffff810c9f8c>] default_idle_call+0x4c/0x60
      [ 7858.221016]  [<ffffffff810ca33b>] cpu_startup_entry+0x39b/0x4d0
      [ 7858.221257]  [<ffffffff8164f995>] rest_init+0x135/0x140
      [ 7858.221469]  [<ffffffff81f83014>] start_kernel+0x50e/0x51b
      [ 7858.221670]  [<ffffffff81f82120>] ? early_idt_handler_array+0x120/0x120
      [ 7858.221894]  [<ffffffff81f8243f>] x86_64_start_reservations+0x2a/0x2c
      [ 7858.222113]  [<ffffffff81f8257c>] x86_64_start_kernel+0x13b/0x14a
      
      Fixes: 2942e900 ("[RTNETLINK]: Use rtnl_unicast() for rtnetlink unicasts")
      Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      2cf75070
  11. 21 9月, 2016 1 次提交
  12. 27 7月, 2016 1 次提交
  13. 17 7月, 2016 1 次提交
    • N
      net: ipmr/ip6mr: add support for keeping an entry age · 43b9e127
      Nikolay Aleksandrov 提交于
      In preparation for hardware offloading of ipmr/ip6mr we need an
      interface that allows to check (and later update) the age of entries.
      Relying on stats alone can show activity but not actual age of the entry,
      furthermore when there're tens of thousands of entries a lot of the
      hardware implementations only support "hit" bits which are cleared on
      read to denote that the entry was active and shouldn't be aged out,
      these can then be naturally translated into age timestamp and will be
      compatible with the software forwarding age. Using a lastuse entry doesn't
      affect performance because the members in that cache line are written to
      along with the age.
      Since all new users are encouraged to use ipmr via netlink, this is
      exported via the RTA_EXPIRES attribute.
      Also do a minor local variable declaration style adjustment - arrange them
      longest to shortest.
      Signed-off-by: NNikolay Aleksandrov <nikolay@cumulusnetworks.com>
      CC: Roopa Prabhu <roopa@cumulusnetworks.com>
      CC: Shrijeet Mukherjee <shm@cumulusnetworks.com>
      CC: Satish Ashok <sashok@cumulusnetworks.com>
      CC: Donald Sharp <sharpd@cumulusnetworks.com>
      CC: David S. Miller <davem@davemloft.net>
      CC: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
      CC: James Morris <jmorris@namei.org>
      CC: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
      CC: Patrick McHardy <kaber@trash.net>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      43b9e127
  14. 10 7月, 2016 1 次提交
  15. 28 6月, 2016 1 次提交
  16. 28 4月, 2016 1 次提交
  17. 22 4月, 2016 1 次提交
  18. 25 11月, 2015 1 次提交
  19. 23 11月, 2015 1 次提交
  20. 08 10月, 2015 1 次提交
  21. 18 9月, 2015 4 次提交
    • E
      netfilter: Pass net into okfn · 0c4b51f0
      Eric W. Biederman 提交于
      This is immediately motivated by the bridge code that chains functions that
      call into netfilter.  Without passing net into the okfns the bridge code would
      need to guess about the best expression for the network namespace to process
      packets in.
      
      As net is frequently one of the first things computed in continuation functions
      after netfilter has done it's job passing in the desired network namespace is in
      many cases a code simplification.
      
      To support this change the function dst_output_okfn is introduced to
      simplify passing dst_output as an okfn.  For the moment dst_output_okfn
      just silently drops the struct net.
      Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      0c4b51f0
    • E
      netfilter: Pass struct net into the netfilter hooks · 29a26a56
      Eric W. Biederman 提交于
      Pass a network namespace parameter into the netfilter hooks.  At the
      call site of the netfilter hooks the path a packet is taking through
      the network stack is well known which allows the network namespace to
      be easily and reliabily.
      
      This allows the replacement of magic code like
      "dev_net(state->in?:state->out)" that appears at the start of most
      netfilter hooks with "state->net".
      
      In almost all cases the network namespace passed in is derived
      from the first network device passed in, guaranteeing those
      paths will not see any changes in practice.
      
      The exceptions are:
      xfrm/xfrm_output.c:xfrm_output_resume()         xs_net(skb_dst(skb)->xfrm)
      ipvs/ip_vs_xmit.c:ip_vs_nat_send_or_cont()      ip_vs_conn_net(cp)
      ipvs/ip_vs_xmit.c:ip_vs_send_or_cont()          ip_vs_conn_net(cp)
      ipv4/raw.c:raw_send_hdrinc()                    sock_net(sk)
      ipv6/ip6_output.c:ip6_xmit()			sock_net(sk)
      ipv6/ndisc.c:ndisc_send_skb()                   dev_net(skb->dev) not dev_net(dst->dev)
      ipv6/raw.c:raw6_send_hdrinc()                   sock_net(sk)
      br_netfilter_hooks.c:br_nf_pre_routing_finish() dev_net(skb->dev) before skb->dev is set to nf_bridge->physindev
      
      In all cases these exceptions seem to be a better expression for the
      network namespace the packet is being processed in then the historic
      "dev_net(in?in:out)".  I am documenting them in case something odd
      pops up and someone starts trying to track down what happened.
      Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      29a26a56
    • E
    • E
      net: Merge dst_output and dst_output_sk · 5a70649e
      Eric W. Biederman 提交于
      Add a sock paramter to dst_output making dst_output_sk superfluous.
      Add a skb->sk parameter to all of the callers of dst_output
      Have the callers of dst_output_sk call dst_output.
      Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      5a70649e
  22. 10 9月, 2015 1 次提交
    • P
      net: ipv6: use common fib_default_rule_pref · f53de1e9
      Phil Sutter 提交于
      This switches IPv6 policy routing to use the shared
      fib_default_rule_pref() function of IPv4 and DECnet. It is also used in
      multicast routing for IPv4 as well as IPv6.
      
      The motivation for this patch is a complaint about iproute2 behaving
      inconsistent between IPv4 and IPv6 when adding policy rules: Formerly,
      IPv6 rules were assigned a fixed priority of 0x3FFF whereas for IPv4 the
      assigned priority value was decreased with each rule added.
      
      Since then all users of the default_pref field have been converted to
      assign the generic function fib_default_rule_pref(), fib_nl_newrule()
      may just use it directly instead. Therefore get rid of the function
      pointer altogether and make fib_default_rule_pref() static, as it's not
      used outside fib_rules.c anymore.
      Signed-off-by: NPhil Sutter <phil@nwl.cc>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      f53de1e9
  23. 06 9月, 2015 1 次提交
  24. 08 4月, 2015 1 次提交
    • D
      netfilter: Pass socket pointer down through okfn(). · 7026b1dd
      David Miller 提交于
      On the output paths in particular, we have to sometimes deal with two
      socket contexts.  First, and usually skb->sk, is the local socket that
      generated the frame.
      
      And second, is potentially the socket used to control a tunneling
      socket, such as one the encapsulates using UDP.
      
      We do not want to disassociate skb->sk when encapsulating in order
      to fix this, because that would break socket memory accounting.
      
      The most extreme case where this can cause huge problems is an
      AF_PACKET socket transmitting over a vxlan device.  We hit code
      paths doing checks that assume they are dealing with an ipv4
      socket, but are actually operating upon the AF_PACKET one.
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      7026b1dd
  25. 03 4月, 2015 4 次提交
  26. 01 4月, 2015 3 次提交
  27. 30 3月, 2015 1 次提交
  28. 13 3月, 2015 1 次提交
    • E
      net: Introduce possible_net_t · 0c5c9fb5
      Eric W. Biederman 提交于
      Having to say
      > #ifdef CONFIG_NET_NS
      > 	struct net *net;
      > #endif
      
      in structures is a little bit wordy and a little bit error prone.
      
      Instead it is possible to say:
      > typedef struct {
      > #ifdef CONFIG_NET_NS
      >       struct net *net;
      > #endif
      > } possible_net_t;
      
      And then in a header say:
      
      > 	possible_net_t net;
      
      Which is cleaner and easier to use and easier to test, as the
      possible_net_t is always there no matter what the compile options.
      
      Further this allows read_pnet and write_pnet to be functions in all
      cases which is better at catching typos.
      
      This change adds possible_net_t, updates the definitions of read_pnet
      and write_pnet, updates optional struct net * variables that
      write_pnet uses on to have the type possible_net_t, and finally fixes
      up the b0rked users of read_pnet and write_pnet.
      Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      Acked-by: NEric Dumazet <edumazet@google.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      0c5c9fb5
  29. 18 1月, 2015 1 次提交
    • J
      netlink: make nlmsg_end() and genlmsg_end() void · 053c095a
      Johannes Berg 提交于
      Contrary to common expectations for an "int" return, these functions
      return only a positive value -- if used correctly they cannot even
      return 0 because the message header will necessarily be in the skb.
      
      This makes the very common pattern of
      
        if (genlmsg_end(...) < 0) { ... }
      
      be a whole bunch of dead code. Many places also simply do
      
        return nlmsg_end(...);
      
      and the caller is expected to deal with it.
      
      This also commonly (at least for me) causes errors, because it is very
      common to write
      
        if (my_function(...))
          /* error condition */
      
      and if my_function() does "return nlmsg_end()" this is of course wrong.
      
      Additionally, there's not a single place in the kernel that actually
      needs the message length returned, and if anyone needs it later then
      it'll be very easy to just use skb->len there.
      
      Remove this, and make the functions void. This removes a bunch of dead
      code as described above. The patch adds lines because I did
      
      -	return nlmsg_end(...);
      +	nlmsg_end(...);
      +	return 0;
      
      I could have preserved all the function's return values by returning
      skb->len, but instead I've audited all the places calling the affected
      functions and found that none cared. A few places actually compared
      the return value with <= 0 in dump functionality, but that could just
      be changed to < 0 with no change in behaviour, so I opted for the more
      efficient version.
      
      One instance of the error I've made numerous times now is also present
      in net/phonet/pn_netlink.c in the route_dumpit() function - it didn't
      check for <0 or <=0 and thus broke out of the loop every single time.
      I've preserved this since it will (I think) have caused the messages to
      userspace to be formatted differently with just a single message for
      every SKB returned to userspace. It's possible that this isn't needed
      for the tools that actually use this, but I don't even know what they
      are so couldn't test that changing this behaviour would be acceptable.
      Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      053c095a
  30. 20 11月, 2014 1 次提交
  31. 31 10月, 2014 1 次提交
  32. 25 8月, 2014 1 次提交
    • I
      ipv6: White-space cleansing : Line Layouts · 67ba4152
      Ian Morris 提交于
      This patch makes no changes to the logic of the code but simply addresses
      coding style issues as detected by checkpatch.
      
      Both objdump and diff -w show no differences.
      
      A number of items are addressed in this patch:
      * Multiple spaces converted to tabs
      * Spaces before tabs removed.
      * Spaces in pointer typing cleansed (char *)foo etc.
      * Remove space after sizeof
      * Ensure spacing around comparators such as if statements.
      Signed-off-by: NIan Morris <ipm@chirality.org.uk>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      67ba4152