Re: Kernel Panic - Unix socket communication in kernel module

[John Baldwin]

On Monday, July 29, 2013 3:31:49 am varanasi sainath wrote:
 Hello,
 
 I am writing a kernel module in which I am trying to connect to a UNIX
 socket
 (UNIX domain sockets use the file system as their address name space).
 Kernel module (loadable) acts as a client and User mode program acts as
 server,
 I have loaded the module using kldload and communication between
 user and kernel module works fine,
 when I try to load the kernel module from loader.conf -
 auto load the kernel module at boot up leads to kernel panic
 as the file system is not ready and kern_connect fails.
 
 How to notify kernel module that File system is ready?
 (any specific event flags)
 
 Is there any specific location for Unix domain socket files?
 (currently created it under /root/soc/socket )
 
 Using MODULE_DEPEND Can I make the module dependent of file system?

You can register a hook for the 'mountroot' EVENTHANDLER event which
will fire after / is mounted.  (You could compare rootvnode against
NULL during module startup to determine if you should defer your
work to the EVENTHANDLER vs doing it right away.)  If you need to
wait for all local filesystems to be mounted, then you will need to
have some userland utility poke your module via a sysctl/ioctl/etc.
after the filesystems are mounted (you could use a custom rc.d script
for this).

-- 
John Baldwin
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Re: Kernel Panic - Unix socket communication in kernel module

[Frank Leonhardt]

On 29/07/2013 08:31, varanasi sainath wrote:

Hello,

I am writing a kernel module in which I am trying to connect to a UNIX
socket
(UNIX domain sockets use the file system as their address name space).
Kernel module (loadable) acts as a client and User mode program acts as
server,
I have loaded the module using kldload and communication between
user and kernel module works fine,
when I try to load the kernel module from loader.conf -
auto load the kernel module at boot up leads to kernel panic
as the file system is not ready and kern_connect fails.

How to notify kernel module that File system is ready?
(any specific event flags)

Is there any specific location for Unix domain socket files?
(currently created it under /root/soc/socket )

Using MODULE_DEPEND Can I make the module dependent of file system?




I shall resist the obvious why question.

I'm assuming you're talking about a fifo here (aka named pipe, and 
occasionally called UNIX socket) rather than the BSD network socket 
interface. IIRC since 4.3BSD fifos have been implemented using sockets 
internally anyway.


Where to put it? I tend to go for /tmp but somewhere in /var might make 
more sense for something that's always supposed to be there.


I don't know how to tell when the FS is ready but it will be when init 
runs, so you might like to try the sysctl variables. Knowing that init 
is always PID 1, the value of kern.lastpid should give a hint. There may 
be an official way of doing this properly.


You could always load the module from rc.local instead.

Regards, Frank.

P.S. You do know that an fd only relates to the kernel thread it's 
currently running in?


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