On Fri, Dec 07, 2007 at 10:43:00AM +0100, Gerald Heinig wrote: > Hi Sonja, > > > Hi everyone. > > > > I'm working on a kernel module that needs to maintain a large > structure > > in memory. As this structure could grow too big to be stored in > memory, > > it would be good to offload parts of it to the disk. What would be the > > best way to do this? Could using a memory-mapped file help? > > How about implementing your code as a system call, which is called from > a process that maps a large file into memory, as you suggested above. > I presume you'd have to handle the question of whether or not your pages > are in memory yourself, ie. pretty much like any other system call. > > Interesting question.
Somewhat related question: What purpose does SYSCALL_MODULE(9) serve? I attempted to use this last month while writing a kernel module of my own, and was never able to get it to work for (what understood to be) a couple different reasons: 1) There's a maximum # of syscalls permitted (see SYS_MAXSYSCALL in include/sys/sycall.h), which means a dynamically-allocated syscall via SYSCALL_MODULE(9) cannot be inserted into the syscalls list. 2) The example code in share/examples/kld/syscall/module/syscall.c specifies the sysent offset as NO_SYSCALL (e.g. -1). You can't pick an arbitrary number here (from what I could tell), because the kernel explicitly ensures that the syscall number being called is not larger than SYS_MAXSYSCALL. This forces you to "steal" a syscall number between 1 and SYS_MAXSYSCALL, no? 3) I tried using a syscall number (115, deprecated vtrace), using it as the offset when calling SYSCALL_MODULE, but the userland program calling syscall(2) returned an error. I didn't research this too thoroughly. As this was the first (only?) kernel module I attempted to write, it's safe to say I'm missing some key knowledge, hence my question. :-) -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB | _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
