svn commit: r198781 - head/lib/libc/sys

[Robert Watson]

On Mon, 2 Nov 2009, Colin Percival wrote:

>  Attempt to reduce accidental foot-shooting by pointing out that
>  accept(2)ed sockets do not necessarily inherit O_NONBLOCK from
>  listening sockets on non-FreeBSD platforms.

I wonder how much trouble we should go to to document bugs in other systems as 
non-portabilities for features that work in our system.  This bug in Linux was 
brought to my attention recently:

        SO_RCVLOWAT and SO_SNDLOWAT
               Specify  the  minimum  number  of  bytes in the buffer until the
               socket layer will pass the data to the protocol (SO_SNDLOWAT) or
               the  user on receiving (SO_RCVLOWAT).  These two values are ini‐
               tialized to 1.  SO_SNDLOWAT is not changeable on Linux (setsock‐
               opt(2)  fails  with  the  error  ENOPROTOOPT).   SO_RCVLOWAT  is
               changeable only since Linux 2.4.  The select(2) and poll(2) sys‐
               tem  calls  currently  do not respect the SO_RCVLOWAT setting on
               Linux, and mark a socket readable when even  a  single  byte  of
               data is available.  A subsequent read from the socket will block
               until SO_RCVLOWAT bytes are available.

I think a more general caution for accept(2) might instead be:

BUGS
 	The inheritence of socket options from a listen socket to a newly
 	accepted socket is inconsistent across protocols, and non-portable.

Robert

>
>  Feet shot:	cperciva
>  MFC after:	1 month
>
> Modified:
>  head/lib/libc/sys/accept.2
>
> Modified: head/lib/libc/sys/accept.2
> ==============================================================================
> --- head/lib/libc/sys/accept.2	Mon Nov  2 06:36:54 2009	(r198780)
> +++ head/lib/libc/sys/accept.2	Mon Nov  2 07:21:13 2009	(r198781)
> @@ -126,6 +126,10 @@ new socket.
> For some applications, performance may be enhanced by using an
> .Xr accept_filter 9
> to pre-process incoming connections.
> +.Pp
> +Portable programs should not rely on the
> +.Dv O_NONBLOCK
> +property being inherited.
> .Sh RETURN VALUES
> The call returns \-1 on error.
> If it succeeds, it returns a non-negative
>