On Thu, 20 Apr 2000, Tigran Aivazian wrote:
> On Thu, 20 Apr 2000, Borislav Deianov wrote:
>
> > On Thu, Apr 20, 2000 at 07:12:03PM +0100, Tigran Aivazian wrote:
> > > On Thu, 20 Apr 2000, Borislav Deianov wrote:
> > > > Modifying sys_call_table from a module works fine but is architecture
> > > > specific (I'm told) and gets intersting when two modules try to
> > > > intercept the same system call.
> > >
> > > this interesting part can be resolved rather straightforward by providing
> > > an (exported) read-write spinlock that is taken for read on each system
> > > call and write by those wishing to modify sys_call_table[]. (this is not
> > > nice because of the effort of taking even a read spinlock on each syscall)
> >
> > Yup, I forgot about that. I was actually thinking about rmmod - a
> > module cannot be safely removed if another one intercepted the same
> > syscall after it (as explained in the Linux Kernel Module Programming
> > Guide). The funny thing is TSRs under DOS had exactly the same problem
> > with interrupts :)
>
> oops, I just realized that I shouldn't have said above or put a smiley in
> front of it :)
>
> Ok, since you fell for it - let's at least make a useful excercise out of
> it - find why my "suggestion" is totally broken...
or at least "totally broken" when taken literally, i.e. holding the
spinlock over the entire syscall. But there is nothing wrong with,
e.g. copying the pointer somewhere safe and private, unlocking the
spinlock and calling it. If, understood in this sense, it seems ok.
Regards,
Tigran.
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