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.
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.
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?
Regards,
Nadia
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
