• Johannes Berg's avatar
    netlink: make nlmsg_end() and genlmsg_end() void · 053c095a
    Johannes Berg authored
    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: default avatarJohannes Berg <johannes.berg@intel.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    053c095a
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