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From: liam@cs.qmw.ac.uk (William Roberts)
Newsgroups: comp.protocols.nfs
Subject: Re: How many clntudp_create() are there in an NFS client?
Summary: Number of clients is compiled in
Keywords: nfs biod udp clntudp_create()
Message-ID: <1818@sequent.cs.qmw.ac.uk>
Date: 22 Mar 90 19:38:55 GMT
References: <6306@umd5.umd.edu>
Reply-To: liam@cs.qmw.ac.uk (William Roberts)
Organization: Computer Science Dept, QMW, University of London, UK.
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The nfsd command opens a single UDP socket, then forks a lot to
make process table entries, then makes a system call to pass
the socket to the kernel routines which take over from there.

The biod processes just fork to make process table slots and
then execute a different system call. This does almost
everything that _exit() does (frees memory etc) but leaves the
process table entries available for associating with read/write
requests.

Entirely separately, whenever the kernel needs to do an rpc to
a remote server, it does an clget to find a free "client
structure" from a table whose size is fixed at compile time.
The free client structure is marked as "in use" and then a
clntudp_create() is called to make a socket if this client
structure has not been used before.

The biod daemons is sitting idle in a queue until the kernel
NFS code notices that the read/write request is flagged as
ASYNCH, in which case an attempt will be made to get a biod to
wait for the I/O rather than the current process. If there
aren't any biods then some other lucky process gets to do the
waiting! You can run without biods - it all still works OK.



To summarise: the number of clntudp_create() calls is limited
by the size of the array of client structures, and has nothing
to do with the number of nfsds, biods or anything else.
-- 

William Roberts                 ARPA: liam@cs.qmw.ac.uk
Queen Mary & Westfield College  UUCP: liam@qmw-cs.UUCP
Mile End Road                   AppleLink: UK0087
LONDON, E1 4NS, UK              Tel:  01-975 5250 (Fax: 01-980 6533)