[CentOS] odd situation slightly off topic (sending file descriptors to another process)

[JohnS]

On Thu, 2010-08-19 at 16:22 -0400, Jerry Geis wrote:
> Jerry Geis wrote:
> > I have coded up the standard sendfd() and recvfd() for linux to send 
> > and recv file descriptors.
> > seems to work 
> > (http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html) 
> >
> > however when I recvfd() my number of open file descriptors bumps by 2 
> > and not 1. (using lsof -p X | wc -l)
> >
> > I am not sure why the count jumps by 2 and not 1. The sendfd() is just 
> > sending a socket descriptor.
> > If I close() the provided descriptor it only closes 1 handle (again 
> > using lsof above).
> >
> > So my recvfd() is giving me 2 but when I close() I only drop 1 and not 
> > 2. Something is not in alignment
> > and just wondering if someone can shed some light on this. Thanks.
> >
> > Jerry
> >
> Here is a diff of the lsof output when a new connection is made and the 
> old connection is closed. The lingering /dev/null is evident. I dont 
> know where that
> is from nor why it does not close upon calling close().
> 
> Jerry
> 
> 13d12
> < kendra  13162 root    4u  IPv4             999539                 TCP 
> devcentos5x64.msgnet.com:6520->am2mm.msgnet.com:52047 (ESTABLISHED)
>  > kendra  13162 root   61u  IPv4             999634                 TCP 
> devcentos5x64.msgnet.com:6520->am2mm.msgnet.com:60390 (ESTABLISHED)
> 73a74
>  > kendra  13162 root   66r   CHR                1,3                1749 
> /dev/null
---
You passing data or what?

You can also do by "lsof -a -p 0000"  "wc" skips things in lsof, you
want every descriptor open
and cat /proc/${PID}/fd/    To make sure.
lsof -i @x.x.x.x for active connections or remaining dead

Passing data to disk fsync() first then close()?

Ahh I read the page you linked and according to it in a client server
like arch the server descriptor will stay open....

"""Closing the descriptor by the sender doesn't really close the file or
device, since the descriptor is still considered open by the receiving
process (even if the receiver hasn't specifically received the
descriptor yet)."""

Kinda what I thought.

ohn