"Ma, Jingbai (Kingboard)" <kingboard.ma at hp.com> writes: > On 3/8/13 6:33 PM, "H. Peter Anvin" <hpa at zytor.com> wrote: > > >>On 03/08/2013 02:06 AM, Jingbai Ma wrote: >>> >>> Kernel do have some abilities that user space haven't. It's possible to >>> map whole memory space of the first kernel into user space on the second >>> kernel. But the user space code has to re-implement some parts of the >>> kernel memory management system again. And worse, it's architecture >>> dependent, more architectures supported, more codes have to be >>> implemented. All implementation in user space must be sync to kernel >>> implementation. It's may called "flexibility", but it's painful to >>> maintain the codes. >>> >> >>What? You are basically talking about /dev/mem... there is nothing >>particularly magic about it at all. > > What we are talking about is filtering memory pages (AKA memory pages > classification) > The makedumpfile (or any other dumper in user space) has to know the > exactly > memory layout of the memory management data structures, it not only > architecture dependent, but also may varies in different kernel release. > At this point, /dev/mem doesn't give any help. > So IMHO, I would like to do it in kernel, rather than So keep tracking > changes in user space code. But the fact is there is no requirment that the crash dump capture kernel is the same version as the kernel that crashed. In fact it has been common at some points in time to use slightly different build options, or slightly different kernels. Say a 32bit PAE kernel to capture a 64bit x86_64 kernel. So in fact performing this work in the kernel and is actively harmful to reliability and maintenance because it adds an incorrect assumption. If you do want the benefit of shared maintenance with the kernel one solution that has been suggested several times is to put code into tools/makedumpfile (probably a library) that encapsulates the kernel specific knowledge that can be loaded into the ramdisk when the crahsdump kernel is being loaded. That would allow shared maintenance along without breaking the possibility of supporting kernel versions. Eric
