Understanding Device Drivers and Kernel Configuration in Operating Systems

1. Drivers and The KernelChapter 12 Presentation by: Kathleen Pensy

2. Purpose Assembles: • Processes • Signals and semaphores • Virtual Memory • File System • Interprocess Communication

3. Terms • Device Driver -A program that extends the operating system to support a device such as a disk or tape drive; or a program that enables an application to use a device such as a printer driver. Hardware devices such as sound cards, printers, scanners, and CD-ROM drives must each have the proper driver installed in order to run. Does not actually have to be associated with a device (ie pseudo terminal). • Module- a piece of kernel code that can be arbitrarily loaded and unloaded during run time. They can be installed and uninstalled as needed. Modules can be arbitrarily loaded at boot time. • Loadable device drivers – a device driver that is implemented as a module.

4. The Kernel • Device drivers • Automatic detection • Load all • Location of build directory build kernel • Solaris /kernel • BSD /usr/src/sys /kernel • Linux /usr/src/linux /boot/vmlinuz

5. Configuring the Kernel • Why? • Unwanted drivers • Drivers not loaded • New hardware • Tailor System –good thing (NOT) • Book’s wrong!!! • Only if you have a really pathetic system • Some exceptions # of tty’s or connections • Brian’s Rule – the cost of more memory or disk space is far less expensive and produces a much greater result than that of the cost of time and pain you will spend trying to optimize your current system. • I.E reasons I don’t support sound cards, and certain devices.

6. Solaris Kernel • Probes and automatically loads • Areas • /kernel – instructions • /platform/platformname (ie Ultra 5) • /platform/hardware sun4u • /usr/kernel • uname - Print certain system information. • Directories pg 227

7. Solaris continued… • /etc/system –very important • rootfs – type of root • rootdev – root partition • forceload – load devices • exclude – do not load devices • moddir – new path to modules • set – set variables • pt_cnt – number of available pty’s • max_nproc – max num. of proc. • maxuprc – max num. of user proc. • Examples: • Set the number of pty’s when too many users are connecting. Had problems on sunserver1 when too many users were trying to ssh in. TTY will be explained later. • Set the number of processes a given user can execute (too many users). • Max_nproc bad idea. Generally

8. Prtconf-general information Sysdef - prtconf on steroids Modinfo – dynamically loaded modules Debugging

9. Linux Kernel • Configuration menus • make xconfig – graphical configuration • make menuconfig curses configuration • Make config command line • .config contains everything about the kernel.

10. Linux continued • Entries in .config • M = enabled as module • Y = compiled into kernel • Compiling kernel: • Cd /usr/src/linux* • mrproper (not mentioned in the book) • make menuconfig • make dep • make clean • make bzImage • make modules • make modules_install

11. Linux continued … • lilo.conf specifies boot process • /sbin/lilo – installs boot loader that will be activated next time you boot • lilo – linux loader, master boot program or secondar. • Always backup your new image • Boot dos/windows partitions as well

12. Fine tuning /proc/sys/fs binfmt_misc dquot-nr inode-nr leases-enable dentry-state file-max inode-state overflowgid dir-notify-enable file-nr lease-break-time overflowuid Not remembered across reboots Try scripts From program sysctl (not mentioned in the book) Kat’s #1 Rule – man page is your friend  Linux continued… Purpose is to allow run-time kernel modification

13. FreeBSD • Similar to linux • Location • /usr/src/sys = source • /usr/src/sys/arch/conf = configuration of kernel • Configuration • Edit conf • Config from conf • Make depend • Make |& tee error • Man –k is your other good friend

14. BSD continued… • /kernel = the kernel back it up • Configuration consists of • machine, cpu, ident, maxusers, options, config, controller, disk, tape, device, pseudo-device • example including nfs in config • options NFS • Disk wd0 at wdc0 disk 0 • Options “CD9660” • Controller isa0 • You can also change configuration on runtime through sysctl as well

15. Device Drivers • Device driver - manages systems interaction w/ a particular piece of hardware. • Configuring a driver for more than 20 computers can be painful - This is why kat thinks linux sucks • New devices = more pain (haha) a new device driver • Never upgrade a driver unless absolutely necessary • Solaris =  easier • Linux =  (Get the picture?) harder • /dev – device files that may link to device drivers • ls –l lists the major and minor • Major = device type • Minor = particular instance of a given device The frustration caused by trying to configure a device driver with certain OS’s

16. Many devices correspond to device files contained in /dev Types: Block – written or read as one block Character – written one byte at a time Standard interfaces: Attach Psize Strategy Close Read Timeout Dump Receive Transmit ioctl resize open Write select probe stop Configuration files Solaris /kernel/drv/*conf /kernel/drv/* HP-UX /stand/system /usr/conf/* Linux /usr/src/linux/.config /usr/src/linux/drivers/* FreeBsd /usr/src/sys/i386/conf/kernel /sys/i386/conf/files* Device files

17. Standard device files • Examples: • Pty –pseudo termnials (ssh,xterm, telnet, rlogin) • A slave and master the slave is actually controlled by the ssh, etc what have you. • Loopback – network interface to local host (send to self) • Rmt – tapes • Rst – scsi tapes • Console device • r= stands for the raw device • Conventions for each are in the hand out. • From Essential Systems Administrators Hand book. ( more clear) • Controller this is where disk is pluged device is the number at which it is attached on that controller. Partition is the slice on that disk. • Create your own device file: • Mknod or makedev

18. Structure Device Drivers Modules Static Device Drivers Loadable device drivers

19. Solaris Specific • Devices • Add • add_drv – loads driver into the kernel • pkgadd – very easy interface • Remove • pkgrm – easy • rem_drv – unload by hand • Modules • Add • modload – loads into the running file system • Remove • modunload – unloads it • Modules can be linked and removed while the kernel is running • Modinfo as seen before shows modules hardwired into the kernel afs, nfs, tcp

20. Linux Specific • Devices • Adding Device driver • cd /usr/src/linux ; patch –p1 < driver.diff • Modules • Add • insmod /path/to/object.o • Modprobe – install or remove into the kernel (can load all modules from a directory) • modprobe -a -t boot • List • lsmod – list modules • Remove • rmmod – remove modules • Modprobe • Can generate dynamic /etc/modules.conf

21. Questions • Anyone have any questions?