Subject: Filesystem buffers in the kernel
To: None <current-users@NetBSD.ORG>
From: Trevin Beattie <>
List: current-users
Date: 03/08/1996 07:47:22
This question is directed to people who write the filesystem drivers.  What
should be the state of a 'struct buf' object both before and after the vnode
which used it is released?

Scenario: when I mount a new filesystem type, I can list the directories and
read a file with no apparent problem (both the terminal output and console
output from printf checkpoints behave as expected).  After reading the file
I unmount the filesystem and run xless to view the /var/log/messages file,
only to find that xless is toast!  "head `which xless`" produces the file I
had read previously from the now-unmounted filesystem.  Fortunately, if I
reboot the kernel or fill the buffers with something else, xless comes back;
so the problem is all in the buffers.

The only thing I can guess is that when I run xless it happens to take the
same 'struct vnode' object that the previous file was using, and the buffer
routines thought the 'struct buf' object for that vnode still had valid
data.  Why?
Trevin Beattie          "Do not meddle in the affairs of wizards,     for you are crunchy and good with ketchup."
      {:->                                     --unknown