On Jun 24, 2009, at 4:44 AM, kernel mailz wrote:
Hi,
I am a newbie, trying to learn but have a few queries, nice if you
could respond
For linux on 85xx systems...
(a) Kernel code runs in PR=0 AS=0 and PID=0, which user space
application run in PR=1 AS=0 and PID 1-255.
Is this correct.
correct.
(b) I am writing a small program where the application code opens
invokes a ioctl call and passes a buffer pointer ( say 0x10000 in
user space)
Now the driver code is using copy_from_user.
How this works internally ?
1. User code executes ioctl
2. interrupt goes to the kernel
On the interrupt the PR changes from 0 -> 1
3. ioctl handler in driver gets invoked
The buffer pointer still contains 0x10000.
How kernel code running in PR=0 accesses it and does the copy. I am
not able to see a address space switch in the asm code of
copy_tofrom_user.
There isn't a address space switch. But address spaces exist at the
same time. The user app is given 0..0xc000_0000 and the kernel uses
0xc000_0000..0xffff_ffff.
- k
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
