Hugh Dickins wrote:
On Thu, 18 Jan 2007, Nadia Derbey wrote:
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.
Ok, I'll do that, thanks!
Regards,
Nadia
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