Hi
I have a problem regarding a procfs entry.
I created one and added a read_func. If I do a
"cat /proc/.../my_entry", debug-printk's show me, that my read function is
called 3 times. It returns 21,19 and 21 bytes.
A "strace cat /proc/.../my_entry" has the following output
...
open("/proc/.../my_entry") = 3
...
read(3,"21 bytes output ...",4096) = 21
write(1,"21 bytes output ...") = 21
read(3,"",4096) = 0
...
close(3)
I have no clue what happens. My module shows me 3 calls of the read function,
but strace shows only 2 (and a return value which is never returned from the
read function). Can anyone explain me what happens here?
The read function
int read_alarm (char *page, char** start, off_t off, int count, int *eof, void *data) {
int diff, ret = 0, len = 0;
unsigned long flags;
MOD_INC_USE_COUNT;
struct netshaper *ns = (struct netshaper*) data;
printk("read_alarm: sem_getcount(1) == %d\n",sem_getcount(&ns->sema_buffer_read));
if (down_interruptible(&ns->sema_buffer_read) == -EINTR) {
printk("read_alarm interrupted\n");
ret = 0;
*eof=1; /* no more data */
goto out;
}
/* operations on the alarm_buffer */
spin_lock_irqsave(ns->alarm_buffer_lock,flags);
char* s = &ns->alarm_buffer[ns->read_index*ALARM_SIZE];
if (strlen(s) > count) {
len = count;
else {
len = strlen(s);
}
/* write out ns->alarm_buffer[ns->read_index*ALARM_SIZE] */
ret = snprintf(page+off,len,"%s",s);
ns->read_index = (ns->read_index+1) % ALARM_BUFFER_LINES;
diff = ns->write_index - ns->read_index;
printk("read_alarm: sem_getcount(2) == %d\n", sem_getcount(&ns->sema_buffer_read));
printk("read_alarm: read_index_new = %d\n",ns->read_index);
spin_unlock_irqrestore(ns->alarm_buffer_lock,flags);
/* check if there are more elements in the buffer */
printk("read_alarm: diff = %d\n",diff);
if (diff != 0) {
/* still some left */
printk ("read_alarm: up(&ns->sema_buffer_read)\n");
up(&ns->sema_buffer_read);
}
*eof=0;
out:
printk("read_alarm: ret = %d\n",ret);
MOD_DEC_USE_COUNT;
return ret;
}
Jörg
--
Da fehlt aber noch die Fehlerbehandlung. Wenn wir die jetzt einbauen,
wird es richtig häßlich. Deshalb ist die Standardfehlerbehandlung in C
meistens der Segmentation Fault." -- Christian Becker
Attachment:
signature.asc
Description: Digital signature
