[LIP] A few queries

Hi,
1)Can kernel directly access the user space address. If it can,
why do we need the macros copy_from_user, copy_to_user etc...
If it can'y why is it so? I have seen in the system call
implementation on x86, eax has the system call index,
ebx,ecx,edx,esi,edi are the registers that has
parameters to the system call. If the no of parametres
are more than five, then they are stored in a structure 
and address of the structure is passed in one of the registers.
Which means to my understanding, we are passing the address in
the user space to the kernel.
2) I read in lot many places, that two tasklets of the same type
can not run simultaneously. But I haven't seen ne type of the
tasklet defined. Does the type mean one of the 4 softirqs. Is it 
like if a keyboard driver raises a tasklet of type TASKLET_SOFTIRQ, 
a sound card diver also raises a tasklet of type TASKLET_SOFTIRQ, 
only one of them will be running and not both a the same time on
SMP. I just want to know is that true. 
Or is it like, two tasklet from the same driver can't be run
simultaneously on diff processors on SMP.
Correct my understanding.
Cheers
Suresh
V.V Suresh Kumar


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