On Wed, Jun 24, 2009 at 6:45 PM, Kumar Gala<ga...@kernel.crashing.org> wrote: > > 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. > Ah Ok, I get it Thanks Kumar
But If the app was running with PID=1, interrupt occurs, kernel code gets executed in PID=1, how does the kernel handle this ? and goes back to PID=0, since its translations are all in PID=0 > - k > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
