[netmp] socket accesses

[Matthew Dillon]

:so_error:
:	The process-side code only ever sets it to 0.
:	I'm thinking I should add a sequence number, incremented every
:	time the proto thread sets so_error. That way, the user side
:	doesn't need to set it to 0 all the time.
    
    There is somewhat of an async race here but it doesn't look like
    the original code really cared about potential races, so I think
    we can avoid the ref count.  If we really needed we could use
    the load-and-clear atomic op (I forget exactly what it is).

:so_sigio: set/unset in process context. proto tests so_sigio and then
:          uses it. This means it can be free()d from under us.
:	  Easier way is probably to add a new netmsg to set/clear
:	  ->so_sigio.

    This works for me.  SIGIO is almost never used so I don't care how
    inefficient it winds up being.

:so_oobmark: soreceive, tcp_input (XXX: should be pretty rare. spinlock?)

    TCP guarantees one OOB mark at a time, so I think this can just
    be a rbytes/wbytes index and that will deal with the race.

:so_aiojobq: used by aio only, which runs under the mplock anyway

    Yah.

:so_upcall{,arg}: XXX accf. netgraph sock, nfs sock should be ok
:	         gets modified in soisconnected() and withing the upcalls
:		 which get run by soisconnected() and sowakeup(). So all
:		 modifications are made in proto thread context and so
:		 are all accesses. I guess we're safe. accf_data and
:		 accf_http mess with the sockbuf, but that socket hasn't
:		 been connected yet, so userspace can't access it. IOW,
:		 I think running without the BGL is ok here. Not so for
:		 netgraph and nfs/smb callbacks. Take the BGL there.
    
    I think the socket code is safe, but the NFS code might not be
    with regards to running without the BGL.  That portion of the NFS
    code could be spin-locked fairly easily.

:so_emuldata: only touched by linux connect, which runs under the mplock
:so_accf: only modified by sockopt code. just change do_setopt_accept_filter()
:         to first clear the SO_ACCEPTFILTER flag and *then* clear so_accf.
:	 (it's already careful to only set the flag after initializing so_accf)
:	 XXX: mem barriers
:
:Opinions?
:
:TIA,
:Aggelos

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>