Training for Ankit (3)

The zap driver:

1. Used wcfxo.c as the datum

2. Created the following dummy functions
wcfxo_open
wcfxo_close
wcfxo_read
wcfxo_write
wcfxo_hooksig

3. Made the hello_spaninit function to initialize the span

4. Made the zaptel settings as I have shown in the first post in this series

5. Start zaptel service

6. Build and insert module

7. Run ztcfg

8. On the console, dial 1000

9. tail -f /var/log/messages should show message from hooksig

10. On the console, hangup

11. tail -f /var/log/messages should show message from hooksig

12. Since syslog buffers the message and does stuff like "Last message repeated X times" you might not see the second message immediately

#include
#include
#include "zaptel.h"

MODULE_LICENSE("GPL");

extern int gpltest;

struct hpvt {
int pos;
struct zt_span span;
struct zt_chan chan;
char variety[128];
}hello;

static int hello_spanInit();

static int hello_init(void)
{
printk(KERN_ALERT "Before: Hello, world %d \n",gpltest);
hello_spanInit();
printk(KERN_ALERT "After: Hello, world\n");
return 0;
}

static void hello_exit(void)
{
printk(KERN_ALERT "Before: Goodbye, cruel world\n");
zt_unregister(&hello.span);
printk(KERN_ALERT "After: Goodbye, cruel world\n");
}

static int wcfxo_open(struct zt_chan *c)
{

printk(KERN_ALERT "Open called\n");
return 0;
}

static int wcfxo_close(struct zt_chan *c)
{

printk(KERN_ALERT "Close called\n");
return 0;
}

static int wcfxo_hooksig(struct zt_chan *chan, zt_txsig_t txsig)
{

printk(KERN_ALERT "Hooksig called\n");
return 0;

}

static int wcfxo_watchdog(struct zt_span *span, int event)
{
printk("FXO: Restarting DMA\n");
return 0;
}


static int hello_spanInit()
{
struct hpvt *wc=&hello;

strcpy(hello.variety,"Thinvent");
hello.pos=0;
/* Zapata stuff */
sprintf(hello.span.name, "SARIN/%d", wc->pos);
snprintf(wc->span.desc, sizeof(wc->span.desc) - 1, "%s Board %d", wc->variety, wc->pos + 1);
sprintf(wc->chan.name, "SARIN/%d/%d", wc->pos, 0);
snprintf(wc->span.location, sizeof(wc->span.location) - 1,"HERE!");
wc->span.manufacturer = "SARIN";
strncpy(wc->span.devicetype, wc->variety, sizeof(wc->span.devicetype) - 1);
wc->chan.sigcap = ZT_SIG_FXSKS | ZT_SIG_FXSLS | ZT_SIG_SF;
wc->chan.chanpos = 1;
wc->span.chans = &wc->chan;
wc->span.channels = 1;
wc->span.hooksig = wcfxo_hooksig;
// wc->span.irq = wc->dev->irq;
wc->span.open = wcfxo_open;
wc->span.close = wcfxo_close;
wc->span.flags = ZT_FLAG_RBS;
wc->span.deflaw = ZT_LAW_MULAW;
wc->span.watchdog = wcfxo_watchdog;
#ifdef ENABLE_TASKLETS
tasklet_init(&wc->wcfxo_tlet, wcfxo_tasklet, (unsigned long)wc);
#endif
init_waitqueue_head(&wc->span.maintq);

wc->span.pvt = wc;
wc->chan.pvt = wc;
if (zt_register(&wc->span, 0)) {
printk("Unable to register span with zaptel\n");
return -1;
}
return 0;

}

module_init(hello_init);
module_exit(hello_exit);

Make file

obj-m += tzap.o
EXTRA_CFLAGS += -I/root/zaptel/kernel

all:
make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules

Training for Ankit (2)

Ok, we built the kernel module. What do we do with it now?

1. Insert the kernel module to kernel
insmod tzap.ko

2. See the messages appearing in /var/log/messages

At this point, Ankit asked me why tail /var/log/messages? Why can't we see that directly?
Ans: Insmod calls the hello_init function. The message comes from

printk(KERN_ALERT "Before: Hello, world %d \n",gpltest);

Now, KERN_ALERT is a priority for kernel messages. ALERT is not a high priority so that the message comes on our Terminal. We changed the line to

printk(KERN_EMERG "Before: Hello, world %d \n",gpltest);

This time, the message appeared on the Terminal. I then showed him /etc/syslog.conf and told him that, it is syslog which reads these messages and decides what to do with it. I showed him my /etc/syslog.conf and explained how various messages are destined to go to various locations.

3. Unloading the module

This is done with the command rmmod tzap. hello_exit is called when this happens.

4. Module license line.

MODULE_LICENSE("GPL"); or something like that tells the module is licensed under GPL license. This has an important for our customer. They will have to GPL the code if they plan to access the symbols that are exported using EXPORT_SYMBOL_GPL. Anyway, they are lucky and zaptel does not have GPL exports.

5. Init & Exit

module_init and module_exit defines the entry points for insmod and rmmod.

6. One more step __init and __exit

These macros tell the kernel that the functions thus defined are specific to module loading and unloading. I told him to remember the Linux boot process and the line "Freeing unused kernel memory". This is possible because if I mark a function as __init, the kernel knows it has no need of the function after initialization. This allows the kernel to free some memory after boot-up