Messages in this thread | | | Date | Fri, 08 Aug 2008 19:04:25 -0400 | From | Oren Laadan <> | Subject | Re: [RFC][PATCH 2/4] checkpoint/restart: x86 support |
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Arnd Bergmann wrote: > On Friday 08 August 2008, Oren Laadan wrote: > >>> It seems weird that you use __u64 members for the registers, but don't >>> include r8..r15 in the list. As a consequence, this structure does not >>> seem well suited for either x86-32 or x86-64. >> In the context of CR, x86-32 and x86-64 are distinct architectures because >> you cannot always migrate from one to the other (though 32->64 is sometimes >> possible). Therefore, each architecture can have a separate checkpoint file >> format (eg r8..r15 only for x86-64). > > So why do you use __u64 members for your 32 bit registers?
The idea was that x86-32 checkpoints can be restarted on a x86-64 node in 32 bit mode. Clearly it needed more thought...
> >> Except for this special case (32 bit running 64 bit), simple conversion can >> be done in the kernel if needed, but most conversion between kernel the >> format for different kernel versions (should it change) can be done in >> user space (eg. with a filter). > > The 32bit on 64bit case is quite common on non-x86 architectures, e.g. > powerpc or sparc, where 64 bit kernels typically run 32 bit user space. > > A particularly interesting case is mixing 32 and 64 bit tasks in a container > that you are checkpointing. This is a very realistic scenario, so there > may be good arguments for keeping the format identical between the variations > of each architecture. > >>> I would suggest either using struct pt_regs by reference, or defining >>> it so that you can use the same structure for both 32 and 64 bit x86. >> We prefer not to use the kernel structure directly, but an intermediate >> structure that can help mitigate subtle incompatibilities issues (between >> kernel configurations, versions, and even compiler versions). >> >> Anyway, either a single structure for both 32 and 64 bit x86, or separate >> "struct cr_hdr_cpu{_32,_64}", one for each architecture. > > struct pt_regs is part of the kernel ABI, it will not change.
I'm in favor about keeping the format identical between the variations of each architecture. Note, however, that "struct pt_regs" won't do because it may change with these variations.
So we'll take care of the padding and add r8..r15 in the next version.
Oren.
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