On Thu, 18 Jan 2007, Nadia Derbey wrote:I find this feature very interesting from a testing perspective. Now, since I don't like the idea of being the only one that uses a feature (not maintained - may be even to be removed?) may be you could advice me on a more broadly used way to get the value of a non exported kernel variable from inside a test running in user mode? should I use /dev/mem instead? But in that case, I should do the virtual to physical conversion myself, right?
Trying to mmap /dev/kmem with an offset I take from /boot/System.map,
I get an EIO error on a 2.6.20-rc4.
This is something that used to work on older kernels.
Had a look at mmap_kmem() in drivers/char/mem.c, and I'm wondering whether
pfn is correctly computed there: shouldn't we have something like
pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) +
__pa(vma->vm_pgoff << PAGE_SHIFT);
instead of
pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + vma->vm_pgoff;
Or may be should I substract PAGE_OFFSET from the value I get from System.map
before mmapping /dev/kmem?
Sigh, you're right, 2.6.19 messed that up completely.
No, you never had to subtract PAGE_OFFSET from that address
in the past, and you shouldn't have to do so now.
Please revert the offending patch below, and then maybe Franck
can come up with a patch which preserves the original behaviour
on architectures which used to work (e.g. i386), while fixing
it for those architectures (which are they?) that did not.
I guess it's reassuring to know that not many are actually
using mmap of /dev/kmem, so you're the first to notice: thanks.