Messages in this thread | | | Subject | [question] What's the difference between /dev/kmem and /dev/mem | From | Steven Rostedt <> | Date | Thu, 11 Aug 2005 17:36:28 -0400 |
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OK, I thought I use to know this. But what is the difference between /dev/kmem and /dev/mem. I thought that with /dev/kmem you could use the actual kernel addresses to read from.
For example, if I wanted to read the current variable X in the kernel, I could look up the address of X in System.map, then mmaping to /dev/kmem I could get to that variable using the address that I got from System.map. But this doesn't seem to work.
I'm getting an IO error on read. And looking at this I see:
static int mmap_kmem(struct file * file, struct vm_area_struct * vma) { unsigned long long val; /* * RED-PEN: on some architectures there is more mapped memory * than available in mem_map which pfn_valid checks * for. Perhaps should add a new macro here. * * RED-PEN: vmalloc is not supported right now. */ if (!pfn_valid(vma->vm_pgoff)) return -EIO; val = (u64)vma->vm_pgoff << PAGE_SHIFT; vma->vm_pgoff = __pa(val) >> PAGE_SHIFT; return mmap_mem(file, vma); }
I printed out the value in vma->vm_pgoff, and it still has the 0xc0000000 (but shifted >> 12). Isn't this suppose to also remove the 0xc? Or am I just totally off here?
Thanks,
-- Steve
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