Subject: upcalls from kernel code to user space daemons
From: Steve French <smfltc@us.ibm.com>
To: linux-kernel@vger.kernel.org
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Organization: IBM
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Date: 14 Jun 2004 13:07:48 -0500
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Is there a good terse example of an upcall from a kernel module (such as
filesystem) to an optional user space helper daemon?   The NFS RPC
example seems more complicated than what I would like as does the
captive ioctl approach which I see in a few places.

I simply need to poke a userspace daemon (e.g. launched by mount) to do
in userspace these two optional functions which are not available in
kernel and pass a small (under 64K) amount of data back to the kernel
module:
1) getHostByName:  when the kernel cifs code detects a server crashes
and fails reconnecting the socket and the kernel code wants to see if
the hostname now has a new ip address.
2) package a kerberos ticket ala RFC2478 (SPNEGO)

And an only very loosely related question - 
The proc interface for returning debug information or stats is somewhat
awkward to use for returned data greater than about 1K - I had trouble
finding a good example of kernel code using /proc to return debug data
larger than that since it involves repeated calls into the pseudofile's
proc read function with careful setting of some offset/lengths which can
be hard when iterating through dynamically generated variable length
debug information.  Is there a good example of that?


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