No, you don't want to put MOD_INC_USE_COUNT in init_module(), thats doomed
for failure.
You want to put it in your open handler. This is the handler that gets
called when a user mode app opens a handle (file descriptor) to your driver
using fd=open("/dev/mydriver",...).
Your driver open() handler should get called and look something like:
static int mydriver_open(struct inode* inode, struct file *file)
{
// Open Device Handle.
// Do what ever you need to here....
// Increment usage counter.
MOD_INC_USE_COUNT;
return 0;
}
When the user closes the drivers handle (e.g. close(fd) ), your driver will
get its release() handler called, at which point it should call
MOD_DEC_USE_COUNT.
So it should look something like this:
static int mydriver_release(struct inode* inode, struct file *file)
{
// Close Device Handle.
// Cleanup code goes here....
// Decrement usage counter.
MOD_DEC_USE_COUNT;
return 0;
}
My understanding is that if you do a:
# rmmod mydriver
and a user has not closed a handle to your driver then the kernel will fail
the rmmod and not call your drivers release handler, which makes sense
right.
I hope now you can see now why calling MOD_INC_USE_COUNT from your
init_module() func is so bad.
John Levon says you should not call MOD_INC_USE_COUNT in the 2.5 kernel at
all.
I am interested to know why he said that, is the 2.5 kernel keeping track of
this internally now John ?
HTH
dom
> -----Original Message-----
> From: Jose Luis Alarcon [mailto:jlalarcon@tiggerfan.com]
> Sent: Sunday, December 08, 2002 4:22 PM
> To: kernelnewbies@nl.linux.org
> Subject: More about MOD_INC_USE_COUNT
>
>
> --- Jose Luis Alarcon <jlalarcon@tiggerfan.com> wrote:
> >--- John Levon <levon@movementarian.org> wrote:
> >>On Sun, Dec 08, 2002 at 12:51:43PM -0800, Jose Luis Alarcon wrote:
> >>
> >>> I has a big surprise when, adding at the beginning of
> init_module()
> >>> the macro MOD_INC_USE_COUNT, for have a module use
> counter. My program
> >>> get compile well and insmod work too.
> >>>
> >>> But the surprise was when i did rmmod, cos the output said:
> >>>
> >>> FATAL: the module is in use
> >>
> >>Why are you surprised ? You marked the module as used by
> something when
> >>you load it, of course it can't be unloaded.
> >>
> >
> > Jonh: first, thank you very much for answer my question.
> >
> > I am surprised cos if the line MOD_INC_USE_COUNT; is
> commented, then
> >the lsmod command say that the module is used by 0 (unused,
> i think) and
> >the rmmod command uninstall the module without nothing to say.
> >
> >>> I did lsmod, and i got that my module was used by [unsafe].
> >>
> >>You should not be using MOD_INC_USE_COUNT in 2.5 kernels. And you
> >>definitely shouldn't be doing it in init_module(), that
> makes no sense.
> >>
> >
> > Can you explain, please, why the macro have no sense in
> init_module()?, maybe
> >(i am thinking about it) use this counter make no sense in
> any place at the
> >module, but i am learning and i only want to see it working.
> >
> >>What do you actually believe MOD_INC_USE_COUNT does ?
> >>
> >
> > I was reading that create a counter that count the number
> of times that the
> >module is used, is it right?
> >
> >>regards
> >>john
> >>
> >
> > Thank you, Jonh, again.
> >
> > Regards.
> >
> > Jose.
> >
>
> One more thing about this:
>
> I put 'MOD_INC_USE_COUNT;' like the last line just before
> the key (}) that
> ends the cleanup_module() void function....and the program
> load with insmod
> and unload with rmmod without problems. lsmod tells that the
> module is used
> by 0 (unused). All this with the 2.5.49 kernel. Maybe was a
> problem of the
> "situation" of the line.......
>
> Regards.
>
> Jose.
>
> Debian GNU/Linux 'Sid' Kernel 2.4.19 Ext3.
> ESware Linux 365 Kernel 2.5.49 ReiserFS.
> Registered Linux User #213309.
> Memories..... You are talking about memories.
> Rick Deckard. Blade Runner.
>
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Archive: http://mail.nl.linux.org/kernelnewbies/
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